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Seasonality in suicides: the influence of suicide method, gender and age on suicide distribution in Italy
Psychiatry Research 81 Ž1998. 219]231
Seasonality in suicides: the influence of suicide method, gender and age on suicide distribution in Italy Antonio Preti a,U , Paola Miotto b a
CMG, Psychiatry Branch, ¨ ia Costantinopoli 42, 09129 Cagliari, Italy b Alcohol and Drug Dependence Unit, Conegliano, TV, Italy
Received 10 March 1998; received in revised form 31 July 1998; accepted 3 August 1998
Abstract In order to ascertain if and how age, gender and choice of lethal means influence the seasonal distribution of suicide in Italy, data concerning all suicides registered in Italy from 1984 to 1995 have been analyzed, taking these variables into account. In the age group 14]65 years and over a total of 31 771 male suicides Žmean yearly rate, 12.6 per 100 000. and 11 984 female suicides Žmean yearly rate, 4.4 per 100 000. have been identified in Italy during the study period. Suicides in the younger age ranges, both among males and females, show a less marked asymmetrical seasonal distribution than those in the older age groups. Only suicides committed by violent methods ŽICD 953]958. show clear evidence of seasonality, with a peak in spring and a low in late autumn. Suicides committed by non-violent methods Ž950]952. follow no seasonal trend in either sex. Spectral analysis reveals a circannual rhythm for violent suicides ŽICD 953]958. in both genders. For male non-violent suicides ŽICD 950]952., a period with a frequency of 0.0833 Ž12 months. has been identified, but with a polarity opposite to that of male violent suicides. For female non-violent suicides, no period of frequency of 0.0833 could be identified, but, as for female violent suicides, a period with frequency close to 0.2500 Ž4 months. has been found. Changes in climate, then, correlate with the monthly distribution of violent and non-violent suicides in opposite ways: male violent suicides show a significant positive relationship with indicators of temperature and exposure to the sun, and a significant negative relationship with indicators of humidity and rainfall. Female suicides show less significant relationships with climate indicators. Work aimed at suicide prevention should therefore take into account the complex influence of seasonal climate both on human biological rhythms Žparticularly on 5-HT related functions and their actions on mood and impulsivity. and on sociorelational habits. Q 1998 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Suicide; Violent suicide; Seasonality; Climate; Serotonin; Social factors
U
Corresponding author. Tel.: q39 70 480922; fax: q39 70 499149; e-mail: [email protected]
0165-1781r98r$ - see front matter Q 1998 Elsevier Science Ireland Ltd. All rights reserved. PII S0165-1781Ž98.00099-7
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1. Introduction An asymmetrical distribution of suicide deaths in relation to the seasons has been reported for as long as reliable statistics on suicide have been available ŽKevan, 1980; Chew and McCleary, 1995.. In the 19th century the Italian Morselli Ž1881. was the first to identify this seasonal component of suicidal mortality, which he attributed to a direct influence on the circuits of the brain of climatic variables, in particular temperature. Durkheim Ž1897. suggested a role for factors of a relational nature; for him the spring peak in suicides observed in many Western countries depended on changes in social intercourse occurring at the beginning of the warm season. The role of mental disorders Žparticularly those with a mood component. as provocative factors for suicide ŽTanney, 1992. has suggested that the seasonal recurrence of disorders leading to suicidal ideation, which often come to prominence in the late winter and in the early spring months ŽWehr and Rosenthal, 1989., might also contribute to the broad seasonal asymmetry in suicide deaths in both hemispheres ŽGoodwin and Jamison, 1990; Preti, 1997.. Climatic influence on the seasonal recurrence of suicides is demonstrated by the opposite distribution patterns in the Southern and Northern hemispheres ŽSwinscow, 1951; Flisher et al., 1997; Yip et al., 1998.. It is more difficult, however, to isolate the influence of a single climatic variable, and to separate biometeorological influence from relational influence ŽSouetre ˆ et al., 1987, 1990; Linkowski et al., 1992; Preti, 1997, 1998.. Not all studies note a clear seasonal asymmetry of suicides. Reid et al. Ž1980., in a sample of Irish suicidal deaths, found no seasonal variation for either gender. Tietjen and Kripke Ž1994. were unable to identify a statistically significant seasonal trend for suicide for Los Angeles County, as were Zacharakis et al. Ž1996. for Athens. Sample composition by age and gender doubtless influences the possibility of observing seasonality in the yearly distribution of suicides; it is likely that influence of climate on suicidal behaviour is different according to the sex and age of the subject. Some studies indicate different seasonal distribu-
tions of suicides for males and females, with a single spring peak for males, and two peaks, one in spring and the other in autumn, for females ŽMeares et al., 1981; Nayha, ¨ ¨ 1982, 1983; Lester and Frank, 1988; Micciolo et al., 1989.. This autumn peak for female suicides may relate to psychosocial processes specific to Western culture, a theory based on the fact that the same trend is not observed in non-Western countries ŽFlisher et al., 1997; Ho et al., 1997; Yip et al., 1998.. As far as age is concerned, some studies of adolescents indicate scarce or zero seasonality in suicides, and more recent studies indicate a more evident seasonality among the elderly than among the young ŽFrank and Lester, 1988.. Yet in New Zealand and Australia, suicidal acts among males aged 15]24 follow a single yearly cycle ŽYip et al., 1998., and pronounced seasonality has been reported for American school-aged male suicides, though with a pattern opposite to that documented for older groups: among the ‘school-aged’ group, suicides peak in winter and reach lows in summer ŽMcCleary et al., 1991.. Age-linked contingencies Žin particular, the coincidence with events in the school year. have been given as explanation. Choice of suicide method has also been found to follow a seasonal pattern. Lester and Frank Ž1988. observed among males spring peaks for suicide by poison, and a bimodal distribution Žtwo peaks, one in spring and the other in autumn. for suicide by hanging or firearm. Females, instead, had spring and autumn peaks for suicide by poison and hanging, and summer and late autumn peaks for firearm suicide. In Australia Yip et al. Ž1998. observed a seasonal trend for suicide by hanging, but found no evidence of method seasonality in their New Zealand sample. In Belgium, Linkowski et al. Ž1992. and Maes et al. Ž1993, 1994, 1995. found that suicide by violent methods shows a clear seasonal trend, whereas suicide by non-violent methods shows no evidence of seasonality. In Israel, Schreiber et al. Ž1993. also observed a seasonal pattern in firearms suicide, but the yearly distribution in their sample is contrary to the distribution observed in many Western countries: colder months have a higher percentage of suicides than warmer months, and
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the peak for suicide is in December. Maes et al. Ž1995. hypothesised that the seasonal variance in suicides depends on an underlying seasonal biological variance, influencing the control of impulses. Serotonergic Ž5-HT. circuits are the most likely explanation for such variance, since brain levels of serotonin are sensitive to climate change, and a clear seasonal rhythm is evident in serotonergic functions, with variations which are a negative reflection of the seasonal distribution of suicide ŽBrewerton, 1989; Maes et al., 1995.. Low levels of serotonin are also often associated with impulsive and aggressive behaviour ŽCoccaro, 1989; Brown and Linnoila, 1990.; it is possible, therefore, that suicide by violent methods, more often committed under the influence of strong impulsive drives, may be particularly influenced by the effects of climate on serotonergic functions. Maes et al.’s hypothesis was based on studies concerning time series of suicides in Belgium. To ascertain if and how age, gender and method chosen for suicide also influence the seasonal distribution of events in Italy, data concerning suicides registered in Italy from 1984 to 1995 have been analyzed and their distribution by age, gender and method according to ICD 9 classification has been taken into account. The role of climate has also been considered. 2. Method Data were taken from the records of the Istituto Nazionale Italiano di Analisi Statistiche ŽISTAT. and are related to the years 1984]1995. Data for death by suicide came from judicial statistics: data were collected from the police and carabinieri Žmilitary police., who compile detailed case reports based on the preliminary death certificate completed by the examining doctor, and on extensive questioning of key informants and relevant witnesses. Classification of suicides was made according to the ninth ŽIX. revision of the ICD ŽInternational Classification of Diseases.. ISTAT data report sex, age, and time distribution of suicides. Analyses refer to these different groups of data. As far as suicide method is concerned, data are
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distributed according to the codes of ICD IX: 950, poisoning by solid or liquid substances; 951, poisoning by gases in domestic use; 952, poisoning by other gases; 953, hanging; 954, submersion; 955, firearms and explosives; 956, cutting and piercing instruments; 957, jumping from high places; 958.0 and 958.5, crashing accident. Following Maes et al. Ž1994., we distinguished nonviolent suicide Ž950]952. from violent suicide Ž953]958.. For the influence of climatic factors on suicidal behaviour, monthly mean suicide values were compared with monthly mean values of climatic indicators over a similar interval of time Ž1974]1994.. The following climatic indicators were considered: mean maximum and minimum temperature Ž8C.; mean degree of humidity Ž%.; mean rainfall Ž1r10 mm of rain.; mean daylight Žh.. Data came from the Meteorological Department of the Italian Air Force, and represent a rough average for the whole of Italy Ži.e. of 17 meteorological stations distributed along the North]South axis of the country.. ANOVA was used to analyse seasonal variance; the data for each month of each season Žfor winter: January, February, March; and so on. were taken into account for the period 1984]1995. Detrended data have been evaluated by spectrum ŽFourier. analysis } used to detect true circannual rhythm. The main aim of spectral analysis is to detect any significant rhythms that may exist in one or more time series. It searches for periodicities in a single time series or in a group of time series on a probabilistic basis: the finding of a significant signal-to-noise ratio in the spectral peaks indicates a true rhythm. A spectrum of all rhythms with a relevant signal-to-noise ratio is constructed, and the five rhythms of highest density periodicity Ža measure of the recurrence of the rhythm. are given separately. The detection of a period with a frequency of 0.0833 would mean that each observation completes 0.0833 of the full cycle, or that 12 observations complete one full cycle Ž12 = 0.0833s 1.. Since the series contains monthly data collected over several years, a periodicity with a frequency of 0.0833 identifies an annual cycle. For details on spectral analysis see Bloomfield Ž1976..
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All analyses were performed on a MacIntosh LC 475 with the Statview package ŽAbacus Concepts, Inc., 1984 Bonuta Ave, Berkeley, CA 94704, USA., except the spectral analysis, performed with the STATISTICA package ŽStatSoft, Inc., 2300 East 14th Street, Tulsa, OK 74104, USA. on an IBM PC.
of suicides is concerned: among both males and females, the young show a less evident asymmetrical distribution by season than the old. Only among those aged 65 and over can a clear seasonal asymmetry be observed in both sexes, with a higher number of deaths in spring than in any other season, and in summer than in winter or autumn ŽFig. 1.. Suicides in both male and female adult age groups also follow a seasonal distribution, albeit a less evident one: among females a secondary peak can be observed in the autumn ŽFig. 1.. A December peak of suicides is observed among youths, while a second peak Žalso observed for adult females. can be seen in April: these peaks fairly coincide with the two major holiday periods of Christmas and Easter. Considered individually, the more violent methods Žjumping from a high place, hanging and submersion, but not weapons. show clear seasonal differences in distribution for men, whereas for women an evident seasonality can be observed for hanging and submersion, and, to a lesser extent, for poisoning with solid or liquid substances ŽTable 2.. When seasonal asymmetries are present, there is a peak in spring, with a low in the late autumn, for both sexes. As a whole, only suicides committed by violent methods ŽICD 953]958. show a clear seasonality, with a peak in spring and a low in late autumn ŽTables 2 and 3, Fig. 2.. Suicides committed by non-violent methods Ž950]952. show no evidence of seasonality in either sex ŽTables 2 and 3, Fig.
3. Results 3.1. Demographic data A total of 31 771 male suicides and 11 984 female suicides were identified in Italy during the 11-year study period, considering the age range of 14]65 years old and over. This corresponds to a yearly mean of 2888 male suicides Žmean yearly rate, 12.6 per 100 000. and a yearly mean of 1089 female suicides Žmean yearly rate, 4.4 per 100 000.. In all age groups more men committed suicide than women: 14]24 years old, ratio m:f s 2625:773; 25]64 years, ratio m:f s 18 427:6745; and 65 years old and older, ratio m:f s 10 719:4466. Standardized suicide rates Žmean yearly rate per 100 000. increase with age: among males, youth s 4.8, adult s 10.4 and elderly s 26.2; among females, youth s 1.4, adult s 3.6 and elderly s 7.4. 3.2. Seasonality As can be seen in Table 1, there are significant differences by age as far as monthly distribution
Table 1 Seasonal differences in suicides by age and gender in Italy, 1984]1995 Winter
Males 14]24 25]64 65 ª Females 14]24 25]64 65
Spring
Summer
Autumn
ANOVA Žd.f.s 3r140.
Mean
S.D.
Mean
S.D.
Mean
S.D.
Mean
S.D.
F
P
18 127 69
5 22 14
18 135 81
5 20 13
17 128 82
4 18 12
18 120 64
12 16 11
0.07 3.68 16.53
0.97 0.01 0.0001
5 44 29
1 9 7
5 52 33
3 13 7
5 46 32
2 9 7
5 43 27
2 9 7
0.76 4.39 5.07
0.51 0.005 0.002
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Fig. 1. Seasonality of suicides: effects of age and gender. Monthly means are illustrated over a 1-year period for completed suicides in Italy Ž1984]1995. according to gender.
Table 2 Seasonal differences in suicides by methods and gender in italy, 1984]1995 Winter
Males Poisoning Poisoning by gas Hanging Jumping from high place Submersion Crashing Weapons Females Poisoning Poisoning by gas Hanging Jumping from high place Submersion Crashing Weapons
Spring
Summer
Autumn
ANOVA Žd.f.s 3r140.
Mean
S.D.
Mean
S.D.
Mean
S.D.
Mean
S.D.
F
P
7 16 69 31 11 5 38
3 7 15 9 5 2 9
7 14 81 35 17 6 38
2 7 16 8 5 3 7
6 12 77 35 10 5 37
2 7 13 7 7 2 8
6 17 62 28 9 6 38
2 14 15 4 4 5 9
1.11 1.80 11.38 5.67 19.47 0.41 0.10
0.34 0.14 0.0001 0.001 0.0001 0.74 0.95
6 3 14 25 9 2 3
2 2 4 6 4 1 2
6 2 18 28 12 2 4
2 2 5 7 4 1 2
6 2 16 28 11 2 3
2 1 5 6 5 1 1
5 3 13 26 8 3 4
1 2 4 7 3 2 3
3.06 1.46 5.97 1.99 6.33 1.44 1.60
0.03 0.22 0.0007 0.11 0.0005 0.23 0.19
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Table 3 Seasonal differences in suicides by methods Žviolent vs. non-violent. in Italy, 1984]1995 Winter
Spring
Summer
Autumn
ANOVA Žd.f.s 3r140.
Mean
S.D.
Mean
S.D.
Mean
S.D.
Mean
S.D.
F
P
Males Non-violent Violent
23 156
7 30
22 179
7 28
19 174
7 25
23 146
15 19
1.69 12.69
0.17 0.0001
Females Non-violent Violent
9 55
3 11
9 66
3 15
8 62
2 13
8 55
3 12
1.80 6.19
0.14 0.0006
Fig. 2. Seasonality of suicides: effects of method. Monthly means are illustrated over a 1-year period for completed suicides in Italy Ž1984]1995. according to gender.
2.. The data do not allow subdivision by age of this picture, so it cannot be excluded that the differences in seasonality between violent and non-violent suicides depend on age distribution of the sample group, with older people using violent methods more often than younger people. Seasonality, however, can be identified not only by the detection of clear differences in the measured variables between different periods of the
year, but also by the identification of a circannual rhythm in the time series of the variables examined and the recognition of peaks and troughs in the chronograms that coincide with specific seasons as defined by climate changes. Spectral ŽFourier. analysis was used to detect true circannual rhythm and revealed such a rhythm for violent suicides ŽICD 953]958. in both genders. For each time series, a cycle with a frequency of 0.0833 was identified among ‘high-density’ periods Ža measure of the recurrence of the rhythm.: this implies that 12 observations complete one full cycle. Since the series contain monthly data collected over several years, this frequency identifies a periodicity that runs on an annual cycle. For male non-violent suicides too ŽICD 950]952. a period with a frequency of 0.0833 was identified over the years, but with an opposite polarity to that of male violent suicides Žcosine coefficient: male violent suicides, y18.89; male non-violent suicides, 3.48.. For female non-violent suicides no period with a frequency of 0.0833 could be identified, but, as for female violent suicides, a period with a frequency close to 0.2500 Ž4 months. was found. Among male non-violent suicides a period with a frequency close to 0.2500 was also identified, with the same polarity as for females, whereas male violent suicides show no infra annual Žintra year. period. 3.3. Influence of climate Climate correlates in opposite ways with the monthly distribution of violent as opposed to
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non-violent suicides. Among males, suicides by violent methods show a significant positive relationship with indicators of temperature and exposure to the sun, and a significant negative relationship with indicators of humidity and rainfall ŽTable 4.. Suicides by non-violent methods, on the other hand, show a significant negative correlation with indicators of temperature and exposure to the sun, and a non-significant positive correlation with indicators of humidity and rainfall ŽTable 4.. Female suicides by violent methods show the same trends as male suicides, whereas none of the correlations observed are significant among female non-violent suicides ŽTable 4.. It should be borne in mind that climatic data in this study are used to support the correspondence of monthly suicide trends with seasonal climate changes: in fact, climatic variables are merely another measure of seasonal rhythm. 4. Discussion This study shows that the seasonal asymmetry in distribution is not an attribute shared by all fatal suicidal events but varies with age, gender and suicide method chosen. For both genders a clear seasonality in the distribution of suicides, with a unimodal distribution and a peak in summer, can be found only in the older age
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group. Among females there is a bimodal pattern in the distribution of suicides, and an additional four-monthly rhythm is observed, both of which trends are absent among males. Finally, in Italy, as in Belgium ŽLinkowski et al., 1992; Maes et al., 1993, 1994, 1995., violent suicides in both genders show evidence of a seasonal trend with a clear recurrent circannual rhythm. The same cannot be said of non-violent suicides. Factors unevenly distributed across age and gender may heavily influence suicidal behaviour, contributing to these findings. Mental disorders seem to be the determinant element in suicidal behaviour: according to studies, a mental disorder is present in up to 90% of suicides ŽTanney, 1992.. Conversely, it is known that approx. 10% of mentally ill patients die by suicide, compared to 0.015]0.050% in the general population ŽTanney, 1992.. In descending order, the conditions carrying the highest risk of suicide are: mood disorders; alcoholism; schizophrenia; personality disorders Žin particular when complicated by addiction.; and anorexia nervosa ŽRoy, 1982; Galanter and Castaneda, 1985; Patton, 1988; Blumenthal, 1988; Henriksson et al., 1993; Isometsa et al., 1994.. The spread of these disorders in the general population is not homogeneous: the frequency of mood disorders increases with age, whereas personality disorders, anorexia nervosa
Table 4 Simple correlational analysis between some climatic variables and suicide by gender and methods, Italy 1984]1995 Male violent suicides
Male non-violent suicides
Ambient Temperature Max Ž8C. Ambient Temperature Min Ž8C. Humidity grade Ž%. Rainfall, mean Ž1r10 mm. Daylight duration Žh.
0.73UU 0.70U y0.89UU y0.74U 0.86U
y0.82UU y0.82UU 0.75U 0.36 y0.75U
Ambient Temperature Max Ž8C. Ambient Temperature Min Ž8C. Humidity grade Ž%. Rainfall, mean Ž1r10 mm. Daylight duration Žh.
Female violent suicides 0.68U 0.66U y0.75U y0.59 0.79U
Female non-violent suicides y0.46 y0.48 0.19 y0.11 y0.26
U
0.12 0.11 0.55 0.71 0.40
P- 0.01, UU P- 0.001 Data concern monthly mean values from 1984]1995 as far as suicides are concerned, and from 1974 to 1994 as far as climatic variables are concerned.
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and, to a lesser extent, schizophrenia all tend towards lower prevalence with increasing age ŽTolstrup et al., 1985; Hare, 1987; Goodwin and Jamison, 1990.. As a consequence, the prevalence of active cases of the latter disorders is lower among the old than among the young, due also to higher precocious mortality rates, which particularly affect sufferers of personality disorders complicated by addiction Žmortality may result from circumstances such as AIDS, deaths by homicide or accident.. Mood disorders, in particular in forms with a clear recurrent trend, follow seasonal patterns in the presentation of episodes more evident than those observed for other mental disorders ŽEastwood and Peacocke, 1976; Parker and Walter, 1982; Wehr and Rosenthal, 1989; Kasper et al., 1989; Faedda et al., 1993.. It is far from rare for patients suffering from a mood disorder with a recurrent trend to end their life with a self-destructive, often violent, act ŽGoodwin and Jamison, 1990.. The different age distribution of disorders leading to suicidal ideation, with greater prevalence of primary and secondary mood disorders among older people, may explain the finding of a more marked seasonality in the older than in the younger groups. A clear seasonal trend in suicides, with a unimodal distribution and a peak in summer, is also observed among older groups in the USA ŽMcCleary et al., 1991., in France ŽSouetre ˆ et al., 1987., and in North Cheshire, UK ŽSalib, 1997.. In Belgium, according to Maes et al. Ž1993., the major contribution to the seasonal trend observed in violent suicides is from the older age groups: in general the elderly frequently use violent methods ŽDe Leo and Ormskerk, 1991.. The different efficiency between age groups of supportive networks contributes to different suicide rates by age ŽDe Leo et al., 1995., and probably also influences the seasonal distribution of suicides. Death by suicide, even when considered at length as a solution to one’s problems, is often precipitated by specific unfavourable life events ŽHart et al., 1988; Heikkinen et al., 1993; Lester, 1995.. Seasonal change greatly influences social intercourse: in warmer months Žspring]summer. human contact is more
frequent, and the possibility of conflict and frustration is also increased. It is in these periods, when many activities neglected in cooler months are restarted, that a scarce relational network, or a network rendered inaccessible by impairing illnesses, may create a limitation or burden. This will often be the case among the elderly, who frequently live in greater isolation. The extent of the supportive network is likely to influence opportunity for a suicidal plan to be carried out. Chew and McCleary Ž1994. suggested that surveillance, together with accessibility of the lethal means, is a key element in suicide: as they state, intense routine surveillance can lower suicide risk even when lethal means are easy to come by. Surveillance of the elderly may decrease in summer, as family and friends spend more time out-of-doors, and this may contribute to the summer peak for elderly suicide. Age- and gender-linked contingencies Žschool, family and work. may generate cycles of age- and gender-specific suicidal risk ŽChew and McCleary, 1994.. In Italy, as in France, a bimodal pattern in the monthly distribution of adult suicides is seen: this pattern, which leads to a secondary peak in autumn, is evident in Italy among females, but is less clear among males. Studies in non-Western countries do not report this bimodal pattern ŽFlisher et al., 1997; Ho et al., 1997; Yip et al., 1998.. It has been argued that Western females experience additional stresses in the autumn, possibly related either to a reduction of social contact in rainy months, or, in the case of married women with school-aged children, to reduced surveillance due to the beginning of the school year: Nayha ¨ ¨ Ž1983. reported that the autumn peak in Finland was marked among married women. Age-linked contingencies may also explain the peculiar suicidal patterns observed among the young: in this study, peaks in the months coinciding with major holidays ŽApril, Easter; December, Christmas. were observed. However, this may also depend on concurrence with the peaks in the beginning of depressive episodes, which are generally in winter and in the early spring ŽWehr and Rosenthal, 1989; Faedda et al., 1993; Preti, 1997..
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So far, there is no clear explanation for the seasonal differences according to method chosen for suicide. Lester and Frank Ž1988., in an American sample limited to a 1-year period, reported a spring peak for suicide by poison for males, and a bimodal distribution for suicide by hanging or firearm, with peaks in spring and in autumn; females, instead, had spring and autumn peaks for suicide by poison and hanging, and summer and late autumn peaks for firearm suicide. In Australia, Yip et al. Ž1998. observed a seasonal trend for suicide by hanging: they found no evidence of method seasonality in their New Zealand sample. In Belgium, Linkowski et al. Ž1992. and Maes et al. Ž1993, 1994, 1995. found that suicide by violent methods showed a clear seasonal trend, whereas suicide by non-violent methods showed no evidence of seasonality. In Israel, Schreiber et al. Ž1993. also observed a seasonal pattern in firearms suicide, but strangely, the distribution in their sample is contrary to the distribution observed in many Western countries: colder months have a higher percentage of suicides than warmer months, and the peak for suicide is in December. The most influential factor in the choice of suicide method is accessibility of the means. Those who live near a high suspension bridge, for example, are more likely to commit suicide by jumping ŽNowers and Gunnell, 1996.. Prescribed drugs are frequently used by patients under treatment: among depressive patients, people who have received their last antidepressant prescription in the previous 30 days are likely to use pills to commit suicide ŽJick et al., 1995.. The role of availability of lethal means in explaining the seasonal distribution of suicides, however, ought not to be of much importance, though its relevance cannot be excluded in some circumstances Žfor seasonal or agricultural workers, for instance .. Similar to the results of studies in Belgium by Linkowski et al. Ž1992. and Maes et al. Ž1993, 1994, 1995., suicides by violent methods in Italy show a seasonal trend with a peak in the late spring months, whereas suicides by non-violent methods show no clear seasonal asymmetry in distribution. Maes et al. Ž1995. suggested that the seasonal variance in serotonergic functions might
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influence the yearly distribution of violent sui˚ cides. The studies of Asberg et al. Ž1987. indicated that the most violent suicide attempts were associated with lower levels of CSF 5-HIAA, the principal metabolite of serotonin, and that this correlation seemed to predict subsequent death by suicide. Most, though not all, post-mortem studies also show defective serotonergic activity in the brains of suicide victims ŽMann, 1995, 1998.. Serotonin has an important role in the control of impulse ŽCoccaro, 1989; Brown and Linnoila, 1990.. Impulsivity, the tendency to react quickly to stimuli, with little consideration of the consequences, is an important component in suicidal ˚ behaviour ŽRoy et al., 1986; Asberg et al., 1987.. Impulsive, externally-directed aggression is associated with low levels of CSF 5-HIAA ŽCoccaro et al., 1989; Virkkunen et al., 1989a.. Individuals suffering from major depression or personality disorders with a history of suicidal behaviour are also more likely to have a history of aggression and impulsivity. In these patients, psychometric measures of impulsivity and aggression negatively correlate with measures of serotonergic function: the lower the serotonergic function, the higher the tendency towards impulsive and aggressive acts, and therefore the higher the risk of suicide ŽCoccaro, 1989.. Freud Ž1917. was the first to claim that suicide could be conceived as the realization of an inhibited homicidal drive deviated towards the self: according to recent studies, some subjects seem especially predisposed to more impulsive behaviour, whether self-directed Žin the form of suicidal behaviour. or externally-directed Žin the form of aggression to property or other persons. ŽMann, 1995, 1998.. Impulsivity often is associated with anger and rage ŽApter et al., 1991; Horesh et al., 1997.: in these cases it is likely that the intention of more impulsive self-destructive acts is to reach the ‘highest level’ of lethality possible. Violent methods are therefore more readily chosen, since the violence of the act is associated with the perception of its lethal irreversibility. For example, murderers who commit suicide tend to use violent methods for suicide, though in these cases the availability of lethal means may be the key factor ŽMarzuk et al., 1992.. Low CSF 5-HIAA has,
228
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however, been shown to be present in impulsive murderers, and reduced serotonergic functioning has been suggested as a prediction of recidivism in violent offenders ŽVirkkunen et al., 1989b; Mann, 1998.. The links between low serotonergic activity and impulsivity may contribute to the seasonality evident in violent suicides reported in this and other studies ŽLinkowski et al., 1992; Maes et al., 1993, 1994, 1995.. A clear seasonal rhythm is evident in serotonergic functions, with variations which are a negative reflection of the seasonal distribution of suicides ŽBrewerton, 1989; Maes et al., 1995.. Suicides committed by non-violent methods Žpoisoning by solid or liquid substances or by gases. require planning to obtain the substance needed to produce a lethal outcome and to avoid rescue intervention; in these cases the role of impulsivity ought to be of lesser importance. Seasonal biological rhythms, as in serotonergic activity, may be synchronized by seasonal weather variations. Serotonin is sensitive to sunlight and also intervenes in the control of body temperature ŽAronson et al., 1993.. Sudden changes in climate, in particular in environmental temperature and humidity degree, are associated with a rise in the number of suicides ŽMaes et al., 1994; Wang et al., 1997.. In addition, the yearly distribution of suicides shows a clear relationship with environmental temperature ŽSouetre ˆ et al., 1987; Maes et al., 1994; Preti, 1997.. In this study, violent suicides in both genders show a clear positive relationship with temperature; non-violent suicides, on the other hand, show a negative correlation with indicators of temperature and exposure to the sun. Climatic data in this study are averaged across the whole of Italy; thus climatic variables are measures of seasonal rhythm. The association of monthly climatic variables with violent suicide simply reflects seasonal changes, and is coherent with those changes. More direct links between weather and suicidal behaviour would need to be investigated at a local level, where it is more likely that weather conditions might influence the biological systems involved in mood and impulse control. Using local climatic data and examining daily associations, some recent studies report sunshine hours and lower levels of relative humidity to be significantly associ-
ated with fatal self-harm in North Cheshire, though with a lower correlation than that reported in this study ŽSalib, 1997; Salib and Gay, 1997.. In Italy, areas with lower levels of relative humidity are associated with higher suicide rates: older people seem more sensitive to climate effects ŽPreti, 1998.. Age- and gender-related differences in the sensitivity of biological systems synchronized with seasonal variations of environmental stimuli may also contribute to seasonal differences in suicide. Serotonin is a potent releaser of ACTH and cortisol, and, conversely, serotonergic functions are inhibited by cortisol ŽChaouloff, 1993.. Mood disorders, which bring the highest risk of suicide of all mental disorders, are often associated with high levels of cortisol ŽGoodwin and Jamison, 1990.: it is possible that hypercortisolism may negatively influence the ability of serotonergic circuits to adapt to sudden changes in homeostasis, such as after relational or environmental Ževen climatic. stress. Clinical neuroendocrinological studies have indeed found evidence of over-activity in the hypothalamic]pituitary]adrenal axis both in completed and in attempted suicides ŽLopez ´ et al., 1997.. Of relevance to this study, violent suicide attempters were found to have higher cortisol levels than those who made nonviolent attempts ŽRoy, 1992.. Gender differences in the sensitivity of biological systems involved in behaviour control to environmental cues may explain the observation of a 4-monthly rhythm among females, which probably also explains why female non-violent suicides show no relationship with climatic variables at a monthly level. A 4-monthly rhythm in female suicides Ži.e. three cycles per year. is also reported in Italy by Micciolo et al. Ž1989., though at a lower significant level than in this study, and by Yip et al. Ž1998. in their New Zealand and Australia samples of suicides, accounting for most of the Žlow. significance of the seasonal component in their study. The female serotonin system appears to be more ‘unstable’ than the male 5-HT system ŽBrewerton and George, 1990.. It is possible that the persistence of a polyphasic rhythm in biological systems influencing suicidal behaviour among females may also have a role in the seasonal
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recurrence of eating disorders and disorders in the sexual sphere, since serotonin intervenes in the control of both eating behaviour ŽBrewerton et al., 1994; Brewerton, 1995. and sexual behaviour ŽGessa and Tagliamonte, 1974; Tagliamonte et al., 1969; Gonzales et al., 1994.. Further study will be needed to explore these hypotheses. Acknowledgements
The authors would like to thank the ISTAT staff in Cagliari for their help and kindness, Gen. Carlo Finizio, from the Meteorology Service of the Italian Air Force, who kindly supplied the climatic data, Dr. PierPaolo Pani for help in performing the Spectral analysis, and Mr. Thomas Eagle for help in the revision of the English translation. The useful suggestions by the referees are gratefully acknowledged. References
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Cosyns, P., Thompson, P., De Meyer, F., Wauters, A., Neels, H., 1995. Seasonal variation in plasma L-tryptophan availability in healthy volunteers. Relationships to violent suicide occurrence. Archives of General Psychiatry 52, 937]946. Mann, J.J., 1995. Violence and aggression, Ch. 163. In: Bloom, F.E., Kupfer, D.J. ŽEds.., Psychopharmacology: The Fourth Generation of Progress. Raven Press, New York, pp. 1919]1928. Mann, J.J., 1998. The neurobiology of suicide. Nature Medicine 4, 25]30. Marzuk, P.M., Tardiff, K., Hirsch, C.S., 1992. The epidemiology of murder]suicide. Journal of the American Medical Association 267, 3179]3183. McCleary, R., Chew, K.S.Y., Hellsten, J.J., Flynn-Bransford, M., 1991. Age- and sex-specific cycles in United States suicides, 1973 to 1985. American Journal of Public Health 81, 1494]1497. Meares, R., Mendelsohn, F.A.O., Milgrom-Friedman, J., 1981. A sex difference in the seasonal variation of suicide rate: a single cycle for men, two cycles for women. British Journal of Psychiatry 138, 321]325. Micciolo, R., Zimmermann-Tansella, C., Williams, P., Tansella, M., 1989. Seasonal variation in suicide: is there a sex difference? Psychological Medicine 19, 199]203. Morselli, E., 1881. Suicide: An Essay on Comparative Statistics. Kegan Paul, London Žoriginal work, Il Suicidio, published in Milan, 1879.. Nayha, ¨ ¨ S., 1982. Autumn incidence of suicides re-examined: data from Finland by sex, age and occupation. British Journal of Psychiatry 141, 512]517. Nayha, ¨ ¨ S., 1983. The bi-seasonal incidence of some suicides. Experience from Finland by marital status, 1961]1976. Acta Psychiatrica Scandinavica 67, 32]42. Nowers, M., Gunnell, D., 1996. Suicide from the Clifton suspension bridge in England. Journal of Epidemiology and Community Health 50, 30]32. Parker, G., Walter, S.D., 1982. Seasonal variation in depressive and suicidal deaths in South Wales. British Journal of Psychiatry 140, 626]632. Patton, G.C., 1988. Mortality in eating disorders. Psychological Medicine 18, 947]951. Preti, A., 1997. The influence of seasonal change on suicidal behaviour in Italy. Journal of Affective Disorders 44, 123]130. Preti, A., 1998. The influence of climate on suicidal behavior in Italy. Psychiatry Research 78, 9]19. Reid, P., Smith, H., Greene, S., 1980. Seasonal variation in Irish suicide deaths. Psychological Reports 46, 306. Roy, A., 1982. Suicide in chronic schizophrenia. British Journal of Psychiatry 141, 171]177. Roy, A., 1992. Hypothalamic]pituitary]adrenal axis function and suicide behavior in depression. Biological Psychiatry 32, 812]816. Roy, A., Virkkunen, M., Guthrie, S., Poland, R., Linnoila, M.,
A. Preti, P. Miotto r Psychiatry Research 81 (1998) 219]231 1986. Monoamines, glucose metabolism, suicidal and aggressive behavior. Psychopharmacology Bulletin 22, 661]665. Salib, E., 1997. Elderly suicide and weather conditions: is there a link? International Journal of Geriatric Psychiatry 12, 937]941. Salib, E., Gay, N., 1997. Weather conditions and fatal self-harm in North Cheshire 1989]1993. British Journal of Psychiatry 170, 473]477. Schreiber, G., Dycian, A., Kaplan, Z., Bleich, A., 1993. A unique monthly distribution of suicide and parasuicide through firearms among Israeli soldiers. Acta Psychiatrica Scandinavica 87, 110]113. Souetre, E., Salvati, E., Belugou, J.L., Douillet, P., Braccini, ˆ T., Darcourt, G., 1987. Seasonality of suicides: environmental, sociological and biological covariations. Journal of Affective Disorders 13, 215]225. Souetre, E., Wehr, T.A., Douillet, P., Darcourt, G., 1990. ˆ Influence of environmental factors on suicidal behaviour. Psychiatry Research 32, 253]263. Swinscow, D., 1951. Some suicide statistics. British Medical Journal i, 1417]1425. Tagliamonte, A., Tagliamonte, P., Gessa, G.L., Brodie, B.B., 1969. Compulsive sexual activity induced by p-chlorophenylalanine in normal and pinealectomized male rats. Science 166, 1433]1435. Tanney, B.L., 1992. Mental disorders, psychiatric patients and suicide, Ch. 14. In: Maris, R.W., Berman, A.L., Maltsberger, J.T., Yufit, R.I. ŽEds.., Assessment and Prediction of Suicide. Guilford Press, New York, pp. 277]320
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Tietjen, G.H., Kripke, D.F., 1994. Suicides in California Ž1968]1977.: Absence of seasonality in Los Angeles and Sacramento Counties. Psychiatry Research 53, 161]172. Tolstrup, K., Brinch, M., Isager, T., Nielsen, S., Nystrup, J., Severin, B., Olesen, N.S., 1985. Long-term outcome of 151 cases of anorexia nervosa. The Copenhagen Anorexia Nervosa follow-up study. Acta Psychiatrica Scandinavica 71, 380]387. Virkkunen, M., De Jong, J., Bartko, J., Linnoila, M., 1989a. Psychobiological concomitants of history of suicide attempts among violent offenders and impulsive fire setters. Archives of General Psychiatry 46, 604]606. Virkkunen, M., DeJong, J., Bartko, J., Goodwin, F.K., Linnoila, M., 1989b. Relationship of psychobiological variables to recidivism in violent offenders and impulsive fire setters. Archives of General Psychiatry 46, 600]603. Wang, Y.T., Wang, D., Wang, X.Y., 1997. Suicide and meteorological factors in Huhhot, inner Mongolia. Crisis 18, 115]117. Wehr, T.A., Rosenthal, N.E., 1989. Seasonality and affective illness. American Journal of Psychiatry 146, 829]839. Yip, P.S.F., Chao, A., Ho, T.P., 1998. A re-examination of seasonal variation in suicides in Australia and New Zealand. Journal of Affective Disorders 47, 141]150. Zacharakis, C., Madianos, M., Papadimitriou, G., Stefanis, C., 1996. Lack of seasonality of suicide in Athens. International Conferences on Suicide: Biopsychosocial approaches, Athens.
Seasonality in suicides: the influence of suicide method, gender and age on suicide distribution in Italy Antonio Preti a,U , Paola Miotto b a
CMG, Psychiatry Branch, ¨ ia Costantinopoli 42, 09129 Cagliari, Italy b Alcohol and Drug Dependence Unit, Conegliano, TV, Italy
Received 10 March 1998; received in revised form 31 July 1998; accepted 3 August 1998
Abstract In order to ascertain if and how age, gender and choice of lethal means influence the seasonal distribution of suicide in Italy, data concerning all suicides registered in Italy from 1984 to 1995 have been analyzed, taking these variables into account. In the age group 14]65 years and over a total of 31 771 male suicides Žmean yearly rate, 12.6 per 100 000. and 11 984 female suicides Žmean yearly rate, 4.4 per 100 000. have been identified in Italy during the study period. Suicides in the younger age ranges, both among males and females, show a less marked asymmetrical seasonal distribution than those in the older age groups. Only suicides committed by violent methods ŽICD 953]958. show clear evidence of seasonality, with a peak in spring and a low in late autumn. Suicides committed by non-violent methods Ž950]952. follow no seasonal trend in either sex. Spectral analysis reveals a circannual rhythm for violent suicides ŽICD 953]958. in both genders. For male non-violent suicides ŽICD 950]952., a period with a frequency of 0.0833 Ž12 months. has been identified, but with a polarity opposite to that of male violent suicides. For female non-violent suicides, no period of frequency of 0.0833 could be identified, but, as for female violent suicides, a period with frequency close to 0.2500 Ž4 months. has been found. Changes in climate, then, correlate with the monthly distribution of violent and non-violent suicides in opposite ways: male violent suicides show a significant positive relationship with indicators of temperature and exposure to the sun, and a significant negative relationship with indicators of humidity and rainfall. Female suicides show less significant relationships with climate indicators. Work aimed at suicide prevention should therefore take into account the complex influence of seasonal climate both on human biological rhythms Žparticularly on 5-HT related functions and their actions on mood and impulsivity. and on sociorelational habits. Q 1998 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Suicide; Violent suicide; Seasonality; Climate; Serotonin; Social factors
U
Corresponding author. Tel.: q39 70 480922; fax: q39 70 499149; e-mail: [email protected]
0165-1781r98r$ - see front matter Q 1998 Elsevier Science Ireland Ltd. All rights reserved. PII S0165-1781Ž98.00099-7
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1. Introduction An asymmetrical distribution of suicide deaths in relation to the seasons has been reported for as long as reliable statistics on suicide have been available ŽKevan, 1980; Chew and McCleary, 1995.. In the 19th century the Italian Morselli Ž1881. was the first to identify this seasonal component of suicidal mortality, which he attributed to a direct influence on the circuits of the brain of climatic variables, in particular temperature. Durkheim Ž1897. suggested a role for factors of a relational nature; for him the spring peak in suicides observed in many Western countries depended on changes in social intercourse occurring at the beginning of the warm season. The role of mental disorders Žparticularly those with a mood component. as provocative factors for suicide ŽTanney, 1992. has suggested that the seasonal recurrence of disorders leading to suicidal ideation, which often come to prominence in the late winter and in the early spring months ŽWehr and Rosenthal, 1989., might also contribute to the broad seasonal asymmetry in suicide deaths in both hemispheres ŽGoodwin and Jamison, 1990; Preti, 1997.. Climatic influence on the seasonal recurrence of suicides is demonstrated by the opposite distribution patterns in the Southern and Northern hemispheres ŽSwinscow, 1951; Flisher et al., 1997; Yip et al., 1998.. It is more difficult, however, to isolate the influence of a single climatic variable, and to separate biometeorological influence from relational influence ŽSouetre ˆ et al., 1987, 1990; Linkowski et al., 1992; Preti, 1997, 1998.. Not all studies note a clear seasonal asymmetry of suicides. Reid et al. Ž1980., in a sample of Irish suicidal deaths, found no seasonal variation for either gender. Tietjen and Kripke Ž1994. were unable to identify a statistically significant seasonal trend for suicide for Los Angeles County, as were Zacharakis et al. Ž1996. for Athens. Sample composition by age and gender doubtless influences the possibility of observing seasonality in the yearly distribution of suicides; it is likely that influence of climate on suicidal behaviour is different according to the sex and age of the subject. Some studies indicate different seasonal distribu-
tions of suicides for males and females, with a single spring peak for males, and two peaks, one in spring and the other in autumn, for females ŽMeares et al., 1981; Nayha, ¨ ¨ 1982, 1983; Lester and Frank, 1988; Micciolo et al., 1989.. This autumn peak for female suicides may relate to psychosocial processes specific to Western culture, a theory based on the fact that the same trend is not observed in non-Western countries ŽFlisher et al., 1997; Ho et al., 1997; Yip et al., 1998.. As far as age is concerned, some studies of adolescents indicate scarce or zero seasonality in suicides, and more recent studies indicate a more evident seasonality among the elderly than among the young ŽFrank and Lester, 1988.. Yet in New Zealand and Australia, suicidal acts among males aged 15]24 follow a single yearly cycle ŽYip et al., 1998., and pronounced seasonality has been reported for American school-aged male suicides, though with a pattern opposite to that documented for older groups: among the ‘school-aged’ group, suicides peak in winter and reach lows in summer ŽMcCleary et al., 1991.. Age-linked contingencies Žin particular, the coincidence with events in the school year. have been given as explanation. Choice of suicide method has also been found to follow a seasonal pattern. Lester and Frank Ž1988. observed among males spring peaks for suicide by poison, and a bimodal distribution Žtwo peaks, one in spring and the other in autumn. for suicide by hanging or firearm. Females, instead, had spring and autumn peaks for suicide by poison and hanging, and summer and late autumn peaks for firearm suicide. In Australia Yip et al. Ž1998. observed a seasonal trend for suicide by hanging, but found no evidence of method seasonality in their New Zealand sample. In Belgium, Linkowski et al. Ž1992. and Maes et al. Ž1993, 1994, 1995. found that suicide by violent methods shows a clear seasonal trend, whereas suicide by non-violent methods shows no evidence of seasonality. In Israel, Schreiber et al. Ž1993. also observed a seasonal pattern in firearms suicide, but the yearly distribution in their sample is contrary to the distribution observed in many Western countries: colder months have a higher percentage of suicides than warmer months, and
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the peak for suicide is in December. Maes et al. Ž1995. hypothesised that the seasonal variance in suicides depends on an underlying seasonal biological variance, influencing the control of impulses. Serotonergic Ž5-HT. circuits are the most likely explanation for such variance, since brain levels of serotonin are sensitive to climate change, and a clear seasonal rhythm is evident in serotonergic functions, with variations which are a negative reflection of the seasonal distribution of suicide ŽBrewerton, 1989; Maes et al., 1995.. Low levels of serotonin are also often associated with impulsive and aggressive behaviour ŽCoccaro, 1989; Brown and Linnoila, 1990.; it is possible, therefore, that suicide by violent methods, more often committed under the influence of strong impulsive drives, may be particularly influenced by the effects of climate on serotonergic functions. Maes et al.’s hypothesis was based on studies concerning time series of suicides in Belgium. To ascertain if and how age, gender and method chosen for suicide also influence the seasonal distribution of events in Italy, data concerning suicides registered in Italy from 1984 to 1995 have been analyzed and their distribution by age, gender and method according to ICD 9 classification has been taken into account. The role of climate has also been considered. 2. Method Data were taken from the records of the Istituto Nazionale Italiano di Analisi Statistiche ŽISTAT. and are related to the years 1984]1995. Data for death by suicide came from judicial statistics: data were collected from the police and carabinieri Žmilitary police., who compile detailed case reports based on the preliminary death certificate completed by the examining doctor, and on extensive questioning of key informants and relevant witnesses. Classification of suicides was made according to the ninth ŽIX. revision of the ICD ŽInternational Classification of Diseases.. ISTAT data report sex, age, and time distribution of suicides. Analyses refer to these different groups of data. As far as suicide method is concerned, data are
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distributed according to the codes of ICD IX: 950, poisoning by solid or liquid substances; 951, poisoning by gases in domestic use; 952, poisoning by other gases; 953, hanging; 954, submersion; 955, firearms and explosives; 956, cutting and piercing instruments; 957, jumping from high places; 958.0 and 958.5, crashing accident. Following Maes et al. Ž1994., we distinguished nonviolent suicide Ž950]952. from violent suicide Ž953]958.. For the influence of climatic factors on suicidal behaviour, monthly mean suicide values were compared with monthly mean values of climatic indicators over a similar interval of time Ž1974]1994.. The following climatic indicators were considered: mean maximum and minimum temperature Ž8C.; mean degree of humidity Ž%.; mean rainfall Ž1r10 mm of rain.; mean daylight Žh.. Data came from the Meteorological Department of the Italian Air Force, and represent a rough average for the whole of Italy Ži.e. of 17 meteorological stations distributed along the North]South axis of the country.. ANOVA was used to analyse seasonal variance; the data for each month of each season Žfor winter: January, February, March; and so on. were taken into account for the period 1984]1995. Detrended data have been evaluated by spectrum ŽFourier. analysis } used to detect true circannual rhythm. The main aim of spectral analysis is to detect any significant rhythms that may exist in one or more time series. It searches for periodicities in a single time series or in a group of time series on a probabilistic basis: the finding of a significant signal-to-noise ratio in the spectral peaks indicates a true rhythm. A spectrum of all rhythms with a relevant signal-to-noise ratio is constructed, and the five rhythms of highest density periodicity Ža measure of the recurrence of the rhythm. are given separately. The detection of a period with a frequency of 0.0833 would mean that each observation completes 0.0833 of the full cycle, or that 12 observations complete one full cycle Ž12 = 0.0833s 1.. Since the series contains monthly data collected over several years, a periodicity with a frequency of 0.0833 identifies an annual cycle. For details on spectral analysis see Bloomfield Ž1976..
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All analyses were performed on a MacIntosh LC 475 with the Statview package ŽAbacus Concepts, Inc., 1984 Bonuta Ave, Berkeley, CA 94704, USA., except the spectral analysis, performed with the STATISTICA package ŽStatSoft, Inc., 2300 East 14th Street, Tulsa, OK 74104, USA. on an IBM PC.
of suicides is concerned: among both males and females, the young show a less evident asymmetrical distribution by season than the old. Only among those aged 65 and over can a clear seasonal asymmetry be observed in both sexes, with a higher number of deaths in spring than in any other season, and in summer than in winter or autumn ŽFig. 1.. Suicides in both male and female adult age groups also follow a seasonal distribution, albeit a less evident one: among females a secondary peak can be observed in the autumn ŽFig. 1.. A December peak of suicides is observed among youths, while a second peak Žalso observed for adult females. can be seen in April: these peaks fairly coincide with the two major holiday periods of Christmas and Easter. Considered individually, the more violent methods Žjumping from a high place, hanging and submersion, but not weapons. show clear seasonal differences in distribution for men, whereas for women an evident seasonality can be observed for hanging and submersion, and, to a lesser extent, for poisoning with solid or liquid substances ŽTable 2.. When seasonal asymmetries are present, there is a peak in spring, with a low in the late autumn, for both sexes. As a whole, only suicides committed by violent methods ŽICD 953]958. show a clear seasonality, with a peak in spring and a low in late autumn ŽTables 2 and 3, Fig. 2.. Suicides committed by non-violent methods Ž950]952. show no evidence of seasonality in either sex ŽTables 2 and 3, Fig.
3. Results 3.1. Demographic data A total of 31 771 male suicides and 11 984 female suicides were identified in Italy during the 11-year study period, considering the age range of 14]65 years old and over. This corresponds to a yearly mean of 2888 male suicides Žmean yearly rate, 12.6 per 100 000. and a yearly mean of 1089 female suicides Žmean yearly rate, 4.4 per 100 000.. In all age groups more men committed suicide than women: 14]24 years old, ratio m:f s 2625:773; 25]64 years, ratio m:f s 18 427:6745; and 65 years old and older, ratio m:f s 10 719:4466. Standardized suicide rates Žmean yearly rate per 100 000. increase with age: among males, youth s 4.8, adult s 10.4 and elderly s 26.2; among females, youth s 1.4, adult s 3.6 and elderly s 7.4. 3.2. Seasonality As can be seen in Table 1, there are significant differences by age as far as monthly distribution
Table 1 Seasonal differences in suicides by age and gender in Italy, 1984]1995 Winter
Males 14]24 25]64 65 ª Females 14]24 25]64 65
Spring
Summer
Autumn
ANOVA Žd.f.s 3r140.
Mean
S.D.
Mean
S.D.
Mean
S.D.
Mean
S.D.
F
P
18 127 69
5 22 14
18 135 81
5 20 13
17 128 82
4 18 12
18 120 64
12 16 11
0.07 3.68 16.53
0.97 0.01 0.0001
5 44 29
1 9 7
5 52 33
3 13 7
5 46 32
2 9 7
5 43 27
2 9 7
0.76 4.39 5.07
0.51 0.005 0.002
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223
Fig. 1. Seasonality of suicides: effects of age and gender. Monthly means are illustrated over a 1-year period for completed suicides in Italy Ž1984]1995. according to gender.
Table 2 Seasonal differences in suicides by methods and gender in italy, 1984]1995 Winter
Males Poisoning Poisoning by gas Hanging Jumping from high place Submersion Crashing Weapons Females Poisoning Poisoning by gas Hanging Jumping from high place Submersion Crashing Weapons
Spring
Summer
Autumn
ANOVA Žd.f.s 3r140.
Mean
S.D.
Mean
S.D.
Mean
S.D.
Mean
S.D.
F
P
7 16 69 31 11 5 38
3 7 15 9 5 2 9
7 14 81 35 17 6 38
2 7 16 8 5 3 7
6 12 77 35 10 5 37
2 7 13 7 7 2 8
6 17 62 28 9 6 38
2 14 15 4 4 5 9
1.11 1.80 11.38 5.67 19.47 0.41 0.10
0.34 0.14 0.0001 0.001 0.0001 0.74 0.95
6 3 14 25 9 2 3
2 2 4 6 4 1 2
6 2 18 28 12 2 4
2 2 5 7 4 1 2
6 2 16 28 11 2 3
2 1 5 6 5 1 1
5 3 13 26 8 3 4
1 2 4 7 3 2 3
3.06 1.46 5.97 1.99 6.33 1.44 1.60
0.03 0.22 0.0007 0.11 0.0005 0.23 0.19
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224
Table 3 Seasonal differences in suicides by methods Žviolent vs. non-violent. in Italy, 1984]1995 Winter
Spring
Summer
Autumn
ANOVA Žd.f.s 3r140.
Mean
S.D.
Mean
S.D.
Mean
S.D.
Mean
S.D.
F
P
Males Non-violent Violent
23 156
7 30
22 179
7 28
19 174
7 25
23 146
15 19
1.69 12.69
0.17 0.0001
Females Non-violent Violent
9 55
3 11
9 66
3 15
8 62
2 13
8 55
3 12
1.80 6.19
0.14 0.0006
Fig. 2. Seasonality of suicides: effects of method. Monthly means are illustrated over a 1-year period for completed suicides in Italy Ž1984]1995. according to gender.
2.. The data do not allow subdivision by age of this picture, so it cannot be excluded that the differences in seasonality between violent and non-violent suicides depend on age distribution of the sample group, with older people using violent methods more often than younger people. Seasonality, however, can be identified not only by the detection of clear differences in the measured variables between different periods of the
year, but also by the identification of a circannual rhythm in the time series of the variables examined and the recognition of peaks and troughs in the chronograms that coincide with specific seasons as defined by climate changes. Spectral ŽFourier. analysis was used to detect true circannual rhythm and revealed such a rhythm for violent suicides ŽICD 953]958. in both genders. For each time series, a cycle with a frequency of 0.0833 was identified among ‘high-density’ periods Ža measure of the recurrence of the rhythm.: this implies that 12 observations complete one full cycle. Since the series contain monthly data collected over several years, this frequency identifies a periodicity that runs on an annual cycle. For male non-violent suicides too ŽICD 950]952. a period with a frequency of 0.0833 was identified over the years, but with an opposite polarity to that of male violent suicides Žcosine coefficient: male violent suicides, y18.89; male non-violent suicides, 3.48.. For female non-violent suicides no period with a frequency of 0.0833 could be identified, but, as for female violent suicides, a period with a frequency close to 0.2500 Ž4 months. was found. Among male non-violent suicides a period with a frequency close to 0.2500 was also identified, with the same polarity as for females, whereas male violent suicides show no infra annual Žintra year. period. 3.3. Influence of climate Climate correlates in opposite ways with the monthly distribution of violent as opposed to
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non-violent suicides. Among males, suicides by violent methods show a significant positive relationship with indicators of temperature and exposure to the sun, and a significant negative relationship with indicators of humidity and rainfall ŽTable 4.. Suicides by non-violent methods, on the other hand, show a significant negative correlation with indicators of temperature and exposure to the sun, and a non-significant positive correlation with indicators of humidity and rainfall ŽTable 4.. Female suicides by violent methods show the same trends as male suicides, whereas none of the correlations observed are significant among female non-violent suicides ŽTable 4.. It should be borne in mind that climatic data in this study are used to support the correspondence of monthly suicide trends with seasonal climate changes: in fact, climatic variables are merely another measure of seasonal rhythm. 4. Discussion This study shows that the seasonal asymmetry in distribution is not an attribute shared by all fatal suicidal events but varies with age, gender and suicide method chosen. For both genders a clear seasonality in the distribution of suicides, with a unimodal distribution and a peak in summer, can be found only in the older age
225
group. Among females there is a bimodal pattern in the distribution of suicides, and an additional four-monthly rhythm is observed, both of which trends are absent among males. Finally, in Italy, as in Belgium ŽLinkowski et al., 1992; Maes et al., 1993, 1994, 1995., violent suicides in both genders show evidence of a seasonal trend with a clear recurrent circannual rhythm. The same cannot be said of non-violent suicides. Factors unevenly distributed across age and gender may heavily influence suicidal behaviour, contributing to these findings. Mental disorders seem to be the determinant element in suicidal behaviour: according to studies, a mental disorder is present in up to 90% of suicides ŽTanney, 1992.. Conversely, it is known that approx. 10% of mentally ill patients die by suicide, compared to 0.015]0.050% in the general population ŽTanney, 1992.. In descending order, the conditions carrying the highest risk of suicide are: mood disorders; alcoholism; schizophrenia; personality disorders Žin particular when complicated by addiction.; and anorexia nervosa ŽRoy, 1982; Galanter and Castaneda, 1985; Patton, 1988; Blumenthal, 1988; Henriksson et al., 1993; Isometsa et al., 1994.. The spread of these disorders in the general population is not homogeneous: the frequency of mood disorders increases with age, whereas personality disorders, anorexia nervosa
Table 4 Simple correlational analysis between some climatic variables and suicide by gender and methods, Italy 1984]1995 Male violent suicides
Male non-violent suicides
Ambient Temperature Max Ž8C. Ambient Temperature Min Ž8C. Humidity grade Ž%. Rainfall, mean Ž1r10 mm. Daylight duration Žh.
0.73UU 0.70U y0.89UU y0.74U 0.86U
y0.82UU y0.82UU 0.75U 0.36 y0.75U
Ambient Temperature Max Ž8C. Ambient Temperature Min Ž8C. Humidity grade Ž%. Rainfall, mean Ž1r10 mm. Daylight duration Žh.
Female violent suicides 0.68U 0.66U y0.75U y0.59 0.79U
Female non-violent suicides y0.46 y0.48 0.19 y0.11 y0.26
U
0.12 0.11 0.55 0.71 0.40
P- 0.01, UU P- 0.001 Data concern monthly mean values from 1984]1995 as far as suicides are concerned, and from 1974 to 1994 as far as climatic variables are concerned.
226
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and, to a lesser extent, schizophrenia all tend towards lower prevalence with increasing age ŽTolstrup et al., 1985; Hare, 1987; Goodwin and Jamison, 1990.. As a consequence, the prevalence of active cases of the latter disorders is lower among the old than among the young, due also to higher precocious mortality rates, which particularly affect sufferers of personality disorders complicated by addiction Žmortality may result from circumstances such as AIDS, deaths by homicide or accident.. Mood disorders, in particular in forms with a clear recurrent trend, follow seasonal patterns in the presentation of episodes more evident than those observed for other mental disorders ŽEastwood and Peacocke, 1976; Parker and Walter, 1982; Wehr and Rosenthal, 1989; Kasper et al., 1989; Faedda et al., 1993.. It is far from rare for patients suffering from a mood disorder with a recurrent trend to end their life with a self-destructive, often violent, act ŽGoodwin and Jamison, 1990.. The different age distribution of disorders leading to suicidal ideation, with greater prevalence of primary and secondary mood disorders among older people, may explain the finding of a more marked seasonality in the older than in the younger groups. A clear seasonal trend in suicides, with a unimodal distribution and a peak in summer, is also observed among older groups in the USA ŽMcCleary et al., 1991., in France ŽSouetre ˆ et al., 1987., and in North Cheshire, UK ŽSalib, 1997.. In Belgium, according to Maes et al. Ž1993., the major contribution to the seasonal trend observed in violent suicides is from the older age groups: in general the elderly frequently use violent methods ŽDe Leo and Ormskerk, 1991.. The different efficiency between age groups of supportive networks contributes to different suicide rates by age ŽDe Leo et al., 1995., and probably also influences the seasonal distribution of suicides. Death by suicide, even when considered at length as a solution to one’s problems, is often precipitated by specific unfavourable life events ŽHart et al., 1988; Heikkinen et al., 1993; Lester, 1995.. Seasonal change greatly influences social intercourse: in warmer months Žspring]summer. human contact is more
frequent, and the possibility of conflict and frustration is also increased. It is in these periods, when many activities neglected in cooler months are restarted, that a scarce relational network, or a network rendered inaccessible by impairing illnesses, may create a limitation or burden. This will often be the case among the elderly, who frequently live in greater isolation. The extent of the supportive network is likely to influence opportunity for a suicidal plan to be carried out. Chew and McCleary Ž1994. suggested that surveillance, together with accessibility of the lethal means, is a key element in suicide: as they state, intense routine surveillance can lower suicide risk even when lethal means are easy to come by. Surveillance of the elderly may decrease in summer, as family and friends spend more time out-of-doors, and this may contribute to the summer peak for elderly suicide. Age- and gender-linked contingencies Žschool, family and work. may generate cycles of age- and gender-specific suicidal risk ŽChew and McCleary, 1994.. In Italy, as in France, a bimodal pattern in the monthly distribution of adult suicides is seen: this pattern, which leads to a secondary peak in autumn, is evident in Italy among females, but is less clear among males. Studies in non-Western countries do not report this bimodal pattern ŽFlisher et al., 1997; Ho et al., 1997; Yip et al., 1998.. It has been argued that Western females experience additional stresses in the autumn, possibly related either to a reduction of social contact in rainy months, or, in the case of married women with school-aged children, to reduced surveillance due to the beginning of the school year: Nayha ¨ ¨ Ž1983. reported that the autumn peak in Finland was marked among married women. Age-linked contingencies may also explain the peculiar suicidal patterns observed among the young: in this study, peaks in the months coinciding with major holidays ŽApril, Easter; December, Christmas. were observed. However, this may also depend on concurrence with the peaks in the beginning of depressive episodes, which are generally in winter and in the early spring ŽWehr and Rosenthal, 1989; Faedda et al., 1993; Preti, 1997..
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So far, there is no clear explanation for the seasonal differences according to method chosen for suicide. Lester and Frank Ž1988., in an American sample limited to a 1-year period, reported a spring peak for suicide by poison for males, and a bimodal distribution for suicide by hanging or firearm, with peaks in spring and in autumn; females, instead, had spring and autumn peaks for suicide by poison and hanging, and summer and late autumn peaks for firearm suicide. In Australia, Yip et al. Ž1998. observed a seasonal trend for suicide by hanging: they found no evidence of method seasonality in their New Zealand sample. In Belgium, Linkowski et al. Ž1992. and Maes et al. Ž1993, 1994, 1995. found that suicide by violent methods showed a clear seasonal trend, whereas suicide by non-violent methods showed no evidence of seasonality. In Israel, Schreiber et al. Ž1993. also observed a seasonal pattern in firearms suicide, but strangely, the distribution in their sample is contrary to the distribution observed in many Western countries: colder months have a higher percentage of suicides than warmer months, and the peak for suicide is in December. The most influential factor in the choice of suicide method is accessibility of the means. Those who live near a high suspension bridge, for example, are more likely to commit suicide by jumping ŽNowers and Gunnell, 1996.. Prescribed drugs are frequently used by patients under treatment: among depressive patients, people who have received their last antidepressant prescription in the previous 30 days are likely to use pills to commit suicide ŽJick et al., 1995.. The role of availability of lethal means in explaining the seasonal distribution of suicides, however, ought not to be of much importance, though its relevance cannot be excluded in some circumstances Žfor seasonal or agricultural workers, for instance .. Similar to the results of studies in Belgium by Linkowski et al. Ž1992. and Maes et al. Ž1993, 1994, 1995., suicides by violent methods in Italy show a seasonal trend with a peak in the late spring months, whereas suicides by non-violent methods show no clear seasonal asymmetry in distribution. Maes et al. Ž1995. suggested that the seasonal variance in serotonergic functions might
227
influence the yearly distribution of violent sui˚ cides. The studies of Asberg et al. Ž1987. indicated that the most violent suicide attempts were associated with lower levels of CSF 5-HIAA, the principal metabolite of serotonin, and that this correlation seemed to predict subsequent death by suicide. Most, though not all, post-mortem studies also show defective serotonergic activity in the brains of suicide victims ŽMann, 1995, 1998.. Serotonin has an important role in the control of impulse ŽCoccaro, 1989; Brown and Linnoila, 1990.. Impulsivity, the tendency to react quickly to stimuli, with little consideration of the consequences, is an important component in suicidal ˚ behaviour ŽRoy et al., 1986; Asberg et al., 1987.. Impulsive, externally-directed aggression is associated with low levels of CSF 5-HIAA ŽCoccaro et al., 1989; Virkkunen et al., 1989a.. Individuals suffering from major depression or personality disorders with a history of suicidal behaviour are also more likely to have a history of aggression and impulsivity. In these patients, psychometric measures of impulsivity and aggression negatively correlate with measures of serotonergic function: the lower the serotonergic function, the higher the tendency towards impulsive and aggressive acts, and therefore the higher the risk of suicide ŽCoccaro, 1989.. Freud Ž1917. was the first to claim that suicide could be conceived as the realization of an inhibited homicidal drive deviated towards the self: according to recent studies, some subjects seem especially predisposed to more impulsive behaviour, whether self-directed Žin the form of suicidal behaviour. or externally-directed Žin the form of aggression to property or other persons. ŽMann, 1995, 1998.. Impulsivity often is associated with anger and rage ŽApter et al., 1991; Horesh et al., 1997.: in these cases it is likely that the intention of more impulsive self-destructive acts is to reach the ‘highest level’ of lethality possible. Violent methods are therefore more readily chosen, since the violence of the act is associated with the perception of its lethal irreversibility. For example, murderers who commit suicide tend to use violent methods for suicide, though in these cases the availability of lethal means may be the key factor ŽMarzuk et al., 1992.. Low CSF 5-HIAA has,
228
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however, been shown to be present in impulsive murderers, and reduced serotonergic functioning has been suggested as a prediction of recidivism in violent offenders ŽVirkkunen et al., 1989b; Mann, 1998.. The links between low serotonergic activity and impulsivity may contribute to the seasonality evident in violent suicides reported in this and other studies ŽLinkowski et al., 1992; Maes et al., 1993, 1994, 1995.. A clear seasonal rhythm is evident in serotonergic functions, with variations which are a negative reflection of the seasonal distribution of suicides ŽBrewerton, 1989; Maes et al., 1995.. Suicides committed by non-violent methods Žpoisoning by solid or liquid substances or by gases. require planning to obtain the substance needed to produce a lethal outcome and to avoid rescue intervention; in these cases the role of impulsivity ought to be of lesser importance. Seasonal biological rhythms, as in serotonergic activity, may be synchronized by seasonal weather variations. Serotonin is sensitive to sunlight and also intervenes in the control of body temperature ŽAronson et al., 1993.. Sudden changes in climate, in particular in environmental temperature and humidity degree, are associated with a rise in the number of suicides ŽMaes et al., 1994; Wang et al., 1997.. In addition, the yearly distribution of suicides shows a clear relationship with environmental temperature ŽSouetre ˆ et al., 1987; Maes et al., 1994; Preti, 1997.. In this study, violent suicides in both genders show a clear positive relationship with temperature; non-violent suicides, on the other hand, show a negative correlation with indicators of temperature and exposure to the sun. Climatic data in this study are averaged across the whole of Italy; thus climatic variables are measures of seasonal rhythm. The association of monthly climatic variables with violent suicide simply reflects seasonal changes, and is coherent with those changes. More direct links between weather and suicidal behaviour would need to be investigated at a local level, where it is more likely that weather conditions might influence the biological systems involved in mood and impulse control. Using local climatic data and examining daily associations, some recent studies report sunshine hours and lower levels of relative humidity to be significantly associ-
ated with fatal self-harm in North Cheshire, though with a lower correlation than that reported in this study ŽSalib, 1997; Salib and Gay, 1997.. In Italy, areas with lower levels of relative humidity are associated with higher suicide rates: older people seem more sensitive to climate effects ŽPreti, 1998.. Age- and gender-related differences in the sensitivity of biological systems synchronized with seasonal variations of environmental stimuli may also contribute to seasonal differences in suicide. Serotonin is a potent releaser of ACTH and cortisol, and, conversely, serotonergic functions are inhibited by cortisol ŽChaouloff, 1993.. Mood disorders, which bring the highest risk of suicide of all mental disorders, are often associated with high levels of cortisol ŽGoodwin and Jamison, 1990.: it is possible that hypercortisolism may negatively influence the ability of serotonergic circuits to adapt to sudden changes in homeostasis, such as after relational or environmental Ževen climatic. stress. Clinical neuroendocrinological studies have indeed found evidence of over-activity in the hypothalamic]pituitary]adrenal axis both in completed and in attempted suicides ŽLopez ´ et al., 1997.. Of relevance to this study, violent suicide attempters were found to have higher cortisol levels than those who made nonviolent attempts ŽRoy, 1992.. Gender differences in the sensitivity of biological systems involved in behaviour control to environmental cues may explain the observation of a 4-monthly rhythm among females, which probably also explains why female non-violent suicides show no relationship with climatic variables at a monthly level. A 4-monthly rhythm in female suicides Ži.e. three cycles per year. is also reported in Italy by Micciolo et al. Ž1989., though at a lower significant level than in this study, and by Yip et al. Ž1998. in their New Zealand and Australia samples of suicides, accounting for most of the Žlow. significance of the seasonal component in their study. The female serotonin system appears to be more ‘unstable’ than the male 5-HT system ŽBrewerton and George, 1990.. It is possible that the persistence of a polyphasic rhythm in biological systems influencing suicidal behaviour among females may also have a role in the seasonal
A. Preti, P. Miotto r Psychiatry Research 81 (1998) 219]231
recurrence of eating disorders and disorders in the sexual sphere, since serotonin intervenes in the control of both eating behaviour ŽBrewerton et al., 1994; Brewerton, 1995. and sexual behaviour ŽGessa and Tagliamonte, 1974; Tagliamonte et al., 1969; Gonzales et al., 1994.. Further study will be needed to explore these hypotheses. Acknowledgements
The authors would like to thank the ISTAT staff in Cagliari for their help and kindness, Gen. Carlo Finizio, from the Meteorology Service of the Italian Air Force, who kindly supplied the climatic data, Dr. PierPaolo Pani for help in performing the Spectral analysis, and Mr. Thomas Eagle for help in the revision of the English translation. The useful suggestions by the referees are gratefully acknowledged. References
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