Summer and winter patterns of seasonality in Chinese college students: A replication

Summer and Winter Patterns of Seasonality in Chinese College Students: A Replication Ling Han, Keqin Wang,

Yiren Cheng,

Zhaoyun

Du, Norman

E. Rosenthal,

and Francois

Primeau

The goal of this study is to replicate an earlier epidemiological finding of seasonal changes in mood and behavior among Chinese medical students using an independent study population. Three hundred nineteen college students were surveyed with a Chinese version of the Seasonal Pattern Assessment Questionnaire (SPAQ) and the Beck Depression Inventory (BDI) in Jining, China, during March of 1996. The frequency of seasonal patterns and prevalence rates of seasonal affective disorder (SAD) were estimated and compared with data from the medical student survey conducted in the same city. The mean Global Seasonality Score (GSS) of this college student sample was 9.9 + 4.9; 84% of the subjects reported some problems with the changing seasons. Summer difficulties were more prevalent than winter difficulties by a ratio of 1.9 to 1 (38.9% Y 20.1%). The estimated rates of summer SAD and subsyndromal-SAD (s-SAD) were 7.5% and

11.9%. respectively, as compared with the corresponding winter figures of 5.6% and 6.3%. In addition, the prevalence estimates of winter pattern or winter SADs were higher in males than in females, but the corresponding summer figures showed no gender difference. Compared with the data from the medical student survey, this college student sample had a higher GSS (P c .Ol) but comparable summer to winter and female to male ratios for the prevalence of SADs (P > .05). These results replicate our previous findings that seasonal problems are common in China, but the predominant problems are summer difficulties rather than winter difficulties, and there is no female preponderance in the prevalence estimates of such problems. Both findings stand in contrast to most Western studies but are consistent with the only other published study performed in the Orient. Copyright 0 2000 by W.B. Saunders Company

S

where the most common estimate of such ratios is between 1.3 and 10.1-5~7-11 However, since this is the only seasonality survey ever conducted in mainland China and the instrument used to define seasonal patterns is derived from Western culture, it is not yet clear whether our findings represent the true existence of a different epidemiological pattern of seasonality in the Chinese population, a phenomenon peculiar to the subpopulation of medical students under survey, or merely measurement errors due to the potential cultural inappropriateness of the SPAQ. As the first step to answer these questions, we conducted a similar epidemiological survey in another college student population to test the generalizability of our findings from the JMC survey.

EASONALITY refers to a regular pattern of changes in human mood and behavior across seasons. In Caucasian populations, seasonality has been associated with a special clinical depressive syndrome, seasonal affective disorder (SAD), or winter depression. Patients suffering from winter SAD usually have depressive episodes in the winter and recover in the summer.’ In the general population of the United States and some European countries, the prevalence rate of winter SAD is estimated to be 1.2% to 9.2%, with 2 of 3 patients being female.‘-9 A milder form of winter SAD, subsyndromal SAD (s-SAD) as defined by Kasper et al.,? is more common. In contrast, summer SAD, an opposite condition to winter SAD as described by Wehr et al., ‘O.” has rarely been reported, and its prevalence estimates were 0% to 3.1% in 3 population surveys in the United States and Iceland? In March 1996, we surveyed 1,358 students of Jining Medical College (JMC) in mainland China using the Seasonal Pattern Assessment Questionnaire (SPAQ).” In contrast to most studies of Caucasian populationsz-9 but consistent with the only other published study in an Oriental population,i3 we observed a preponderance of summer SAD over winter SAD, with a summer to winter rate ratio of SAD prevalence of 1.5. In addition, we found that the female to male ratios for both winter SAD (0.89) and summer SAD (0.92) were close to 1, which also disagrees with most Western studies, Comprehensive

Psychiatry,

Vol. 41, No. 1 (January/February),

METHODS This survey was conducted at Jining Education College from March 14 to 21, 1996, in the same city (Jining, China; latitude 35.4”N) and using the same instruments (SPAQ and Beck Depression Inventory [BDI]) and procedure as our medical

From the National Institute of Mental Health. Clinical Psychobiology Branch. Bethesda. MD: and Jining Medical College and the Ajiliated Psychiatric Hospital, Jining. China. Address reprint requests to Ling Han, M.D., do Francois Primeau. M.D., Department of Psychiaty, St-Mary’s Hospital Cente< McGill Utliversity, 3830 Lacombe Ave. Montreal Que H3T I MS. Canada. Copyright 0 2000 by WB. Saunders Company 0010-440x/00/4101-0005$10.00/0

2000: pp 57-62

57

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student survey. A description of the methods for the survey has been reported elsewhere.6 In brief, a Chinese translation of the

product-moment or Spearman method. Since gender and age were among the most documented risk factors of seasonality,‘-i’

SPAQ was prepared to adapt the content to Chinese culture and to facilitate administration of the questionnaire in a classroom

we evaluated the effects of gender analysis of covariance (ANCOVA)

setting. To maximize cooperation and ensure adequate sample size, all full-time students enrolled in the college were invited to participate. The, purpose and procedure of the survey were

variable summer

veyed with the SPAQ and BDI under the supervision instructor and an investigator in their own classrooms. tion and return the confidential in China. Based

study. All

a winter pattern of seasonality was in at least I of the months of worst”

and

February.

and

a summer

pattern

Seasonality

and a rating

seasonal behavioral changes as at least a moderate problem: for s-SAD. a GSS of 10 or greater plus no more than problems. These clinical diagnostic group of clinically

Getter-d

of seasonality

in the United

and mild

States and

Descriptive statistics (mean 2 SD and prevalence rates) were calculated in the total sample and in different seasonal patterns or types of SAD. Simple correlations between age, or BDI total score (BDIT) were analyzed

Table

the GSS and sex. using the Pearson

1. Characteristics

of Different

Female Age (yr)t§ (mean

Winter Pattern (n = 641

Summer Pattern In = 124)

235 (73.7)

56 (87.5)

77 (62.1)

84 (26.3)

8 (12.5)

47 (37.9)

34.3 -t 2.6 9.9 2 4.9

GSSt§ the seasons

34.3 -c 2.4 9.7 t 4.5

34.2 z 2.6 10.2 -c 4.9

1.8

1.8

NS

1.5 1.7

NS NS

1.4

1.3

1.6

Appetite Energy

1.6

1.7

1.7

are at least a moderate problem, the course of 1 year (mean kg)*

n (%)*

1.8 109 (34.3)

Autumn BDITt§

l chi-square §Mean

P values

1.8 29 (45.3)

1.9 36 (29.3)

NS NS NS ,026

2.1

2.0

2.2

NS

8.5 7.9 6.8

7.9 7.6 6.8

8.5 7.9 6.6

,046 NS NS

7.6

NS

h)S

Spring Summer

NOTE.

NS NS

1.8 1.8

(mean

,001

1.5

Mood Weight

Sleep length Winter

P

rating)* 1.3 1.9

Changes with the season Weight fluctuation during

SAS

Patterns

TOtal Sample (N = 319)

Sex, (%I” Male

with

with

of the Study Population

Itfotmntiot~

Seasonality

Characteristic

Item scores on changes Sleep length Social activity

performed

All 319 eligible students participated in this survey and returned their completed questionnaires on-site. The rate of missing data was low, from 1% to 0% across the variables under study. Of the 3 19 subjects, 235 were male (73.6%) and 84 were female (26.4%). The mean age was 34.3 + 2.6 years (n = 3 16: range, 27 to 4 1). The subjects were highly homogeneous with regard to education (all college students), marital status (all married), and residency area (all living in the same latitude areas at least 3 years).

of

criteria have been reported to have good validity by Kasper et al.? against a known diagnosed SAD patients. and are used in

most population surveys other countries.3-9~iz~‘3

were

RESULTS

Global

of I I or higher

procedures

as

worst in at least I of the months of June. July. and The case identification criteria for an interview-based proposed by Kasper et al.? were used. i.e.. for SAD. a (GSS)

of the statistical

6.21 software.”

feeling August. survey

Score

of the 2 seasonal patterns were compared of variance (ANOVA). chi-square test, and

student sample using chi-square (x2) tests with Mantel-Haenszel correction or ANOVA. as appropriate to each variable under

SPAQ.

defined as “feeling December. January.

and by

Wilcoxon rank sum test. as specified in Table I. In addition. data from this sample were compared with data from the medical

of their Comple-

of the questionnaires was regarded as consent for use of the data in reports, as is standard practice

on the

or BDIT with as a grouping

and age as a covariate. Prevalence rates for winter pattern or winter and summer SADs were compared

LI test. Characteristics using l-way analysis

explained to the students with the approval and assistance of the school authority. On scheduled class time. students were sur-

on the GSS using gender

7.3

7.0

10.0 f 8.1 are derived

test (df = 1). tl-way -e SD.

from

comparisons

ANOVA

between

summer

(df = 1. 185), SWilcoxon

score

and winter (rank

patterns

sum) test.

11.3 2 8.3 using

the following

9.2 + 8.3 statistical

NS methods:

SEASONALITY

PATTERNS

Prevalence

qf Seasonal

IN CHINESE

COLLEGE

STUDENTS

Problems

The mean GSS for the total sample was 9.9 + 4.9 (N = 319) with an approximate normal distribution (skewness = 0.17, kurtosis = -0.29). Only 8 subjects (2.5%) did not notice any seasonal change in the 6 aspects of mood and behavior. Fifty-one (16.0%) subjects thought their behavioral changes over a season were not a problem, while 109 (34.3%) rated such changes as at least a moderate problem. No significant correlation was found between the GSS and age (Pearson’s r = - .076, P = .176, n = 3 16) or sex (Spearman’s r = - .080, P = .150, N = 3 19). ANCOVA on the GSS using sex as a grouping factor and age as a covariate did not reveal a significant main effect (for the model. F = 2.42, df= 2, 305. P = .090). The BDI score for this sample was IO.0 2 8. I, with a positive correlation with the GSS (Pearson’s r = .149, P = .008, N = 319). Figure 1 shows the frequency distribution of months endorsed by the subjects for feeling worst, against the profile of the average daily ambient temperature and daily sunshine hours across the months of year in this area. An obvious summer peak with the highest percentage of 26.6% in July and a winter subpeak of 11.3% in December were observed. One hundred twenty-four (38.9%) subjects could be classified as a summer pattern and 64 (20.1%) as a winter pattern. The prevalence of the summer pattern was significantly higher than that of the winter pattern ((/ = 5.21, df= 1, P < .OOl). In addition, 8 subjects (2.5%) endorsed both summer and winter months for feeling worst. To avoid potential misclassification, these individuals were excluded from either the winter or the summer pattern. The estimated prevalence rates were 5.6% ( 18 of 3 19) for winter SAD, 6.3% (20 of 3 19) for winter s-SAD, 7.5% (24 of 319) for summer SAD, and 11.9% (38 of 3 19) for summer s-SAD, respectively. The combined rate of summer SAD and s-SAD was significantly higher than the corresponding winter figure (19.4% v 11.9%, U = 2.61, P < .Ol). But the rates of summer SAD and winter SAD alone did not differ significantly (7.5% 1’5.6%, P > .05). The combined rate of winter SAD and s-SAD was higher in males than in females (15.7% v 2.4%. U = 3.15, P < .Ol), whereas the corresponding summer figure showed no gender difference ( 18.8% 1’ 23.20/n, U = 0.85, P > .05).

59

Characteristics of Winter and Summer Patterns of Seasonality

Table 1 shows the main characteristics of the study population. No significant difference between winter and summer patterns emerged for age (F = 0.02, df = 1, 184, P = .882), GSS (F = 0.56, df = 1,186, P = .454), or BDIT (F = 2.59, df = 1,186, P = .109). But the winter pattern had a lower female to male ratio (xz = 13.16, df = 1, P < .OOl), a shorter sleep time in winter (Wilcoxon rank sum test, Z = - 1.99, P = .046), and more persons complaining of moderate or worse problems due to seasonal changes (x2 = 4.95, df = 1, P = .026).

Each of the 4 SAD higher GSS than the F = 32.13, df = 4,310, a difference on the df = 4,310, P = .084).

Comparison

groups had a significantly non-SAD group (overall P = .OOOl) and a trend for BDIT (overall F = 2.08,

With the Medical

Student

Sample

Compared with the medical student sample, this sample had more male subjects (73.6% v 60.1%, x2 = 19.47, df = 1, P = .OOOl) and was older (34.3 v 20.7 years). The mean GSS of this sample was also higher than that of the JMC sample (9.9 v 8.3, F = 45.03, df = 1, 1582, P = .OOOl), and the difference remained in both genders. The mean BDIT did not differ between the 2 samples (F = 0.93, df = 1, 1582, P = .34). No significant differences were observed in the frequency distribution of winter or summer seasonal patterns (Mantel-Haenszel x’ = 2.777, df = 1, P = .096) or in the estimated rates of winter or summer SAD (Mantel-Haenszel x’ = 0.8 16, df = 1, P = .366). The summer to winter rate ratios for seasonal patterns (1.9 v 1.5) and for SAD (1.6 v 1.5) were comparable between the 2 populations (Mantel-Haenszel x’ = 1.77, and 0.073, df = 1, P = .183 and .787, respectively). DISCUSSION This study replicates our previous findings on seasonal changes in mood and behavior in Chinese medical students. Summer difficulty was more common than winter difficulty either in terms of the general seasonal pattern of feeling worst or by the SPAQ-based SAD case finding criteria. In addition,

HAN

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ET AL.

30.0 25.0 E

20.0

2 E

15.0

s c LL

10.0 5.0 0.0

Month

Seasonal

Variation

of Year

of Feeling

Worst

A

DAT

(oC)

DSH

Average Daily Ambient Temperature (DAT) 8 Sunshine Hours (DSH)

B it confirms the lack of female preponderance in seasonally affected individuals observed in the medical student population. Both findings contrast sharply with most Western studies,‘-s.7-9 but are consistent with the only other published study in Asia.i3 In this later study, Ozaki et al.” observed a similar preponderance of summer difficulty in Japanese civil servants, although the overall level of seasonality in that population was much lower than ours. In the Western studies, only 7.6% to 18.5% of the population reported feeling worst during summer, as compared with 43% to 50% during winteP; similarly, prevalence estimates of winter SAD mostly outnumbered summer SAD at a ratio between 1.3 and IO.‘,”

(hrs)

Fig 1. (A) Seasonal variation for feeling worst in the study populations. (B) Average daily ambient temperature (DAT) and daily sunshine hours (DSH).

There is nothing particularly severe about summer in Jining City as compared with some of the climates in which the Caucasian studies were performed. However, the paralleling curves of monthly ambient temperature and daylight hours and the frequency distribution of feeling worst in our 2 study populations in Fig 1 suggest temperature to be one of the susceptible environmental risk factors for summer difhculty. It is also possible that genetic differences in people who have evolved in different climates might explain the different susceptibility to summer and winter responses in different ethnic groups.i5 To the contrary, stress would seem an unlikely explanation, as the more stressed medical students had a similar prevalence of SADs as their nonmedical counterparts.

SEASONALITY

PATTERNS

IN CHINESE

COLLEGE

STUDENTS

It is unclear whether the lack of gender difference in the prevalence estimates of SADs is attributable to environmental, cultural, or genetic factors. In the National Comorbidity Study, Blazer et ali6 found that the gender ratio is significantly different between major and minor depressionwith a seasonalpattern (DWSPs), with females predominating in minor and males predominating in major DWSP. If such an observation is generalizable to the SPAQ-defined SAD groups, the relatively high female to male ratio in the summer pattern may suggest it to be a less severe condition than its winter counterpart. Another consistent finding in our studies is that a great majority of the population reported some seasonal problems, with a normally distributed GSS as shown in Fig 2. In Western studies, a right-skewed distribution of the GSS was usually observed.*~‘r~r’As the Chinese population is a SAD-nave population and an effort was made to avoid conveying a pathological implication of seasonality to students during the survey, it is unlikely that a systematic bias would have occurred with these college students’ reporting of seasonal problems; in addition, the mean BDI score of this sample is comparable to that of the JMC sample, as well as to another college student sample in Hong Kong,rE which would rule out the possibility that the observed high GSS and prevalence rates of SADs might result from overreporting by the subjects. Thus, this normal distribution provides epidemiological evidence for a continuous spectrum hypothesis of seasonality. 11.17 Nevertheless,the SPAQ-basedcase-finding criteria may still be a potential source of overestimating the prevalence of SADs. As reported by Blazer et al, I6 the prevalence estimates of major and minor depression with a seasonal pattern using a clinical diagnostic interview were much lower than those of SADs derived from the SPAQ-based criteria. This finding suggests that the SPAQ-defined seasonal syndromes may not be fully equivalent to the clinical entity of SAD or DWSPs, especially in a nonoccidental culture or population. Unfortunately, whether and to what degree such potential overestimation has biased our prevalence estimates of SADs cannot be determined by this study, due to the lack of clinical interview of those potential SAD “cases.”

61

Fig 2. Frequency populations.

distribution

of the

GSS

in the

study

This study provides additional epidemiologic evidence for the existence of 2 forms of seasonal@ syndromes. Winter SAD seems universal across countries, latitudes, or ethnic populations2-g,r2~13 regardless of whether the ambient temperature in winter is extremely cold (Iceland, Alaska, etc.) or hot (Florida), whereas summer SAD seems more common in areaswhere the ambient temperature in summer is very hot (Florida) or less adjustable (China and Japan), but is rare in very cold areas (Iceland). In addition, a number of clinical studies addressing biological markers and the effect of light therapy suggest that patients with winter SAD may have some biological susceptibility to the lack of light and the circadian rhythm disturbance.‘~i’+‘7 A recent twin study that tested the relative contribution of genetic and environmental factors to seasonal symptoms in Australia provides further support for a biological-heterogeneity model of SADs.i5 This study found that genetic effects seemsto play an important role in the winter type of seasonality rather than the summer type. Thus, further studies are needed to investigate the relationship between 2 polar-opposite seasonality syndromes, especially from an environmental-genetic interaction perspective. ACKNOWLEDGMENT We are deeply indebted to all of the teachers and students of Jining Education College for their participation in this survey, and to Drs. D.C. Chao, S.Z. Jin, Z.H. Su, L.G. Ren, and P. Han of Jining Medical College-Afiiliated Psychiatric Hospital for their assistance in collecting the data. We thank Dr. Tong-Ping So from Taipei Veterans General Hospital for his critical review and valuable comments on the Chinese version of the SPAQ.

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