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Involvement in physical activity and risk for nearly lethal suicide attempts
Involvement in Physical Activity and Risk for Nearly Lethal Suicide Attempts Thomas R. Simon, PhD, Kenneth E. Powell, MD, MPH, Alan C. Swann, MD Background: Although substantial research suggests that involvement in physical activity is associated with mental health benefits, relatively little is known about the association between physical activity and suicidal behavior. This study compared reports of recent physical activity among those surviving a nearly lethal suicide attempt to reports from community controls. Methods:
Analyses were conducted on data collected between November 1992 and July 1995 for a population-based, case– control study of nearly lethal suicide attempts among people aged 13 to 34 years. Logistic regression analyses were used to test the association between suicide attempts and physical activity, including the intensity, frequency, and duration of activity, while controlling for demographic factors and potential explanatory variables, such as depression, alcoholism, and the presence of a serious medical condition.
Results:
Suicide attempters were far less likely than controls to report involvement in physical activity in the past month (48% vs 85%, respectively). Intensity, frequency, and duration of activity did not affect this association. The association persisted after adjusting for demographics and potential explanatory variables.
Conclusions: Additional research is needed to explain the process through which the association occurs. The strong protective association observed is consistent with other research on the mental health benefits of physical activity and recommendations of involvement in regular physical activity. (Am J Prev Med 2004;27(4):310 –315) © 2004 American Journal of Preventive Medicine
Introduction
T
he physical health benefits associated with an active lifestyle are extensive, including improvements in the cardiovascular, musculoskeletal, metabolic, endocrine, and immune systems.1 Substantial research suggests that involvement in physical activity may provide mental health benefits as well, such as lower levels of depression and hopelessness. These effects on mood suggest a possible protective association between physical activity and risk for suicide. Relatively few studies have examined the association between physical activity and suicidal behavior directly, and those that have show inconsistent results. For example, several studies of adolescents and young adults have found evidence of inverse associations between sports participation or physical activity and suicidal ideation or behavior, while others have found a protective association for males and no effect, or even From the Division of Violence Prevention, National Center for Injury Prevention and Control, Centers for Disease Control and Prevention (Simon), and Georgia Department of Human Resources, Division of Public Health (Powell), Atlanta, Georgia; and University of Texas– Houston Mental Science Institute (Swann), Houston, Texas Address correspondence and reprint requests to: Thomas Simon, PhD, Mailstop K-60, National Center for Injury Prevention and Control, Centers for Disease Control and Prevention, 4770 Buford Highway, Atlanta GA 30341-3724. E-mail: [email protected]
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higher risk, among more-active females.2–5 These studies included suicide attempters, who are likely to be quite different from those who die from suicide. A prospective longitudinal investigation of the association between physical activity and actual suicides found that the 129 suicide victims in the follow-up sample did not differ on baseline levels of physical activity collected 23 to 27 years earlier.6 The lack of a protective effect for suicide may mean that the effect was not present, that it was not strong enough to be tested with a sample of this size, that the effect is of shorter duration, or that levels of physical activity changed over time. Substantially more evidence is available for an association between involvement in physical activity and mood. For example, people often report using exercise to cope with depressive symptoms.7 Exercise frequency is inversely associated with loneliness, shyness, and hopelessness among adolescents.8 Those who exercise regularly experience an increase in depressive symptoms when their exercise patterns are interrupted.9,10 Moreover, the immediate improvements in mood following exercise appear to be stronger for those who were feeling relatively depressed prior to exercising.11 Experimental studies provide some of the strongest support for the beneficial effect of physical activity on mood. Numerous studies with diverse samples have
Am J Prev Med 2004;27(4) © 2004 American Journal of Preventive Medicine • Published by Elsevier Inc.
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shown that people who are exposed to an intervention that increases their level of physical activity report lower levels of depression.12–14 A review of exercise intervention studies concluded that aerobic exercise is more effective than a control condition and not significantly different from other intervention strategies in the treatment of unipolar depressive disorders.15 These findings suggest a plausible mechanism for a protective influence of physical activity on the risk for suicidal behavior. To the extent that those who are physically active experience a more positive affect, it is possible that they would be at lower risk for suicidal behavior. This study examined the association between nearly lethal suicide attempts (NLSAs) and involvement in physical activity, including the intensity, frequency, and usual duration of activity among adolescents and young people aged 13 to 34 years. This study is intended to extend earlier research on the association between physical activity and suicide risk in at least two important ways. First, case– control methodology was used to examine those who survived an NLSA. These attempters either used highly lethal methods or they had injuries that were likely to be fatal had they not received emergency medical intervention, and therefore they are more like people who actually die from suicide than people who make less-lethal suicide attempts.16 This methodology permitted a comparison of recent levels of physical activity among nearly lethal attempters to the levels reported by a sample of community controls. Second, the potential explanatory role of indicators of mental health status, such as depressive symptoms, hopelessness, and social support, as well as indicators of poor health status, was examined. Poor physical health is associated with an inability to exercise and risk for suicidal behavior.17,18 Therefore, it is important to control for factors that may indicate poor health status, such as alcoholism, obesity, and recognized medical illness, when testing the association between involvement in physical activity and suicide risk.
Methods Sample This analysis uses data from a population-based, case– control study of NLSAs occurring within a defined catchment area of Houston, Texas. A more detailed description of the sample and procedures is available elsewhere.19 The sample consisted of 153 case and 513 control subjects interviewed from November 1992 through September 1995. Participation in the study was limited to youths and young adults aged 13 to 34 years residing in the central area of Houston, circumscribed by a major highway (Beltway 8).
Case Identification During the study period, an evaluating psychiatric physician completed a form indicating the method and severity of injury for all suicide attempters presenting at the three major
trauma centers serving the Houston population. These three hospitals were selected because they capture the vast majority of the NLSAs within Houston.19 The form, described in detail elsewhere, has been shown to provide a reliable assessment of the medical severity of the attempt.16 In an NLSA, the attempter was likely to have died from suicide had they not received emergency medical or surgical intervention, or the attempter unequivocally employed a method with a high case–fatality ratio (e.g., gunshot wounds and hanging) and sustained an injury, regardless of severity. Of the 1648 suicide attempters meeting the time period, age, and residency requirements, 244 (15%) met the criteria for an NLSA. Among these 244 eligible attempters, 153 (63%) were interviewed, 54 (22%) refused, 22 (9%) denied attempting suicide, 4 (2%) were too ill to be interviewed, and 11 (5%) were lost to follow-up. Patients who agreed to be in the study did not differ from eligible patients who declined on age, gender, or race. The study participants were less likely to be Hispanic and were more likely to have ingested poisons or pills and less likely to have used a firearm than nonparticipants.19
Control Identification Control subjects from the catchment area were enlisted via a random-digit-dial telephone survey during the same time period in which case subjects were enrolled. Control subjects were contacted and screened for age and residence eligibility (13 to 34 years of age, residence within Beltway 8). Of the 4875 telephone numbers contacted, 857 (18%) produced an eligible control subject; 2890 (59%) had no resident within the age range; 1033 (21%) refused to be screened; and 93 (2%) resided outside Beltway 8. Of the 857 eligible control subjects, 513 (60%) completed the in-person interview; 230 (27%) refused to participate when first contacted by telephone; 53 (6%) refused an interview in the field; and 61 (7%) failed to complete the field interview for some other reason (e.g., could not be located, did not appear for interview). The control subjects were similar to the population of Harris County aged 13 to 34 with respect to gender, age, and race/ethnicity.19 To ensure seasonal comparability, potential control subjects were contacted during the same time period in which case subjects were enrolled.
Procedures Case interviews. Case subjects were interviewed after permission was obtained from the responsible physician and the patient (and patient’s guardian, if a minor). Over 75% of participants were interviewed within 7 days of their attempt, and all interviews were completed within 33 days. Seventyeight percent of cases were interviewed in the hospital, 12% at home, and 10% at other locations. Administration of the case interview required an average 44 minutes. Control interviews. Control subjects were interviewed at the home (61%) or workplace (11%) of the subject or at a public location (28%) such as a library or restaurant, depending on the subject’s preference. The average length of the control interview was 37 minutes. Each case and control subject was paid $15 for his or her time upon completing the interview.
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Measures Physical activity. Four questions were used to assess recent physical activity. First, subjects were asked whether they participated in “any physical activities or exercises such as running, calisthenics, golf, gardening, or walking for exercise” in the month before the suicide attempt (or interview for the control subjects). Respondents were then asked to report the type of activity that they spent “the most time doing” during the month, the amount of time they usually spent doing this activity, and the number of times per week they took part in this activity during that month. The primary physical activity was assigned a metabolic equivalent (MET) value based on an established classification and coded as vigorous (MET value ⬎6.0, such as running); moderate (MET value between 4 and 6, such as dancing); or light (MET value ⬍4, such as walking).20,21 The total MET minutes per week were calculated by multiplying the MET value by the number of days and number of minutes that the respondent usually took part in this activity. For ease of interpretation, four categories of MET minutes were created (⬎1260 MET minutes, 420 to 1260 MET minutes, ⬍420 MET minutes, and none). Using the MET value of 3.5 for walking as a reference, the cut-points of 420 and 1260 MET minutes correspond to approximately 2 and 6 hours of walking, respectively. Potential confounders. Respondents provided their gender, age, and race/ethnicity. The Center for Epidemiologic Studies Depression Scale (CES-D) was used to assess depressive symptoms. The 20-item CES-D has been shown to have adequate test–retest reliability and a high degree of internal consistency.22 Participants with CES-D scores ⬎15 were considered depressed. Feelings of hopelessness about the future were assessed with the 20-item true–false Beck Hopelessness Scale. A dichotomous hopelessness variable was created, with scores ⬎8 coded as hopeless.23 This scale has shown high internal consistency, and a strong agreement with clinical ratings of hopelessness.24,25 In the current sample, respondents were asked to report whether they experienced symptoms of depression and hopelessness during the week before the suicide attempt (or the week before the interview, for control subjects). Both measures were found to have a high degree of internal consistency (Cronbach’s alpha was 0.93 for depressive symptoms and 0.87 for hopelessness). A modified version of the Veterans Alcoholism Screening Test was used to detect symptoms of alcoholism within the past year.26 Respondents also were asked if they have “any serious medical problems or conditions.”18 Body mass index (BMI) was calculated using respondents’ self-reports of height and weight. The distribution of BMI scores among controls was used to categorize individuals’ BMI as low (i.e., lowest 25%), medium (i.e., middle 50%) or high (i.e., highest 25%). Reports of having discussed health or emotional problems with a friend or family member in the past 30 days (coded as yes or no) was included as a proxy indicator of social support.
Analysis A series of multivariable logistic regression analyses was used to test the relevant associations. The first model tested the extent to which the demographic characteristics of gender, age, and race/ethnicity, as well as the six potential confounders— depression, hopelessness, alcoholism, the presence of a
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serious medical condition, body mass index, and use of social support—were independently associated with involvement in physical activity. The second model simultaneously tested the extent to which the same demographic characteristics and potential confounders were independently associated with risk for an NLSA. Separate logistic regression models were then analyzed to test the associations between NLSAs and any physical activity in the past month, as well as intensity, frequency, duration, and MET minutes of activity per week. Each physical activity variable was tested separately, first alone and then after adjusting for the demographic characteristics of gender, age, and race/ethnicity, and all six potential explanatory variables. Two-way interaction terms for gender and depression were included in the adjusted models for each measure of physical activity to test whether results varied by gender or depressive symptom status.
Results Involvement in Physical Activity While 85% of the control participants reported engaging in physical activity in the past month, fewer than half (i.e., 48%) of the nearly lethal attempters reported being physically active in the month before their suicide attempt. Overall, involvement in physical activity was significantly more likely among males and those who had used social support (Table 1). Older participants and those who reported symptoms of depression or hopelessness were significantly less likely to report involvement in physical activity.
Predictors of Nearly Lethal Suicide Attempts NLSAs were significantly more common in males than females, and in Hispanics than non-Hispanic whites. These attempts were also significantly more likely among those who reported symptoms of depression, hopelessness, and alcoholism, and those who reported having a serious medical condition. The only potential explanatory factors examined that were not significantly associated with risk for a NLSA were BMI and the use of social support.
Association Between Physical Activity and Nearly Lethal Suicide Attempts Crude and adjusted odds ratios for each of the physical activity variables were calculated next. None of the interaction terms for gender or depression by physical activity was statistically significant. Therefore, only the main effect terms were retained in the model. Even after adjusting for the full set of potential confounders, risk for NLSAs was five times higher among those who had not been physically active in the past month (Table 2). Those who were physically active were at lower risk than those who were not, regardless of the intensity, frequency, or usual duration of their primary physical activity. Relative to those who were active five or more times per week, those who were inactive were at signif-
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Table 1. AORsa for participation in physical activity and nearly lethal suicide attempts by demographic characteristics and potential confounders Physically active Characteristics of the entire sample Gender Female (362) Male (304) Age 13–18 (188) 19–34 (478) Race/ethnicity Hispanic (149) NH Black (173) NH White (327) Depressed No (370) Yes (294) Hopeless No (516) Yes (145) Alcoholism No (527) Yes (121) Medical condition No (557) Yes (109) Body mass index Low (169) Medium (330) High (160) Social support used No (347) Yes (319)
Attempters
%
AOR
(95% CI)
%
AOR
(95% CI)
73.5 80.3
1.00 1.79
(1.16–2.76)
19.3 27.3
1.00 1.79
(1.03–3.10)
83.5 73.9
1.00 0.46
(0.28–0.77)
25.0 22.2
1.00 0.65
(0.37–1.16)
72.5 71.7 81.0
1.00 1.06 1.62
(0.61–1.83) (0.97–2.70)
30.2 31.8 15.3
1.00 1.02 0.27
(0.52–2.00) (0.14–0.53)
86.2 64.3
1.00 0.41
(0.25–0.69)
6.0 44.6
1.00 3.08
(1.61–5.87)
82.4 57.2
1.00 0.48
(0.28–0.80)
9.1 70.3
1.00 17.51
(9.27–33.08)
78.9 66.1
1.00 0.74
(0.45–1.24)
18.6 43.0
1.00 2.13
(1.15–3.94)
78.1 68.8
1.00 0.82
(0.48–1.39)
19.0 43.1
1.00 2.61
(1.37–5.00)
75.7 79.7 70.6
1.00 1.41 0.94
(0.86–2.32) (0.54–1.64)
24.9 23.0 20.6
1.00 1.51 0.88
(0.79–2.88) (0.41–1.87)
74.9 78.4
1.00 1.54
(1.01–2.33)
22.5 23.5
1.00 0.77
(0.45–1.31)
AOR, adjusted odds ratio; CI, confidence interval. a The results are from a simultaneous multivariable logistic regression model that included all the variables listed in the table.
icantly greater risk, and those who were less frequently active (i.e., one to two or three to four times per week) were at lower risk. However, the overall indicator of physical activity, MET minutes per week, showed no difference across the levels of MET minutes among those who were active. Those in the highest level of MET minutes per week were at significantly lower risk for NLSAs than those who were inactive.
Discussion The results indicate that the likelihood of an NLSA was substantially higher among those who reported no physical activity in the past month. This association remained after adjusting for demographic characteristics and potential confounders, including depression, hopelessness, alcoholism, presence of a serious medical condition, BMI, and social support. However, no dose– response to intensity, frequency, or duration, either alone or when combined as MET minutes per week, was observed. Estimates of physical inactivity from a nationally representative sample of young U.S. adults suggest that the control subjects were similar to the national
average. The results from the 1992 National Behavioral Risk Factor Surveillance System indicated that 18.9% of males and 25.4% of females aged 18 to 29 reported no participation in leisure-time physical activity.1 The subset of control subjects recruited for the current study who were aged 18 to 29 had comparable levels of inactivity, with 15.0% of males and 25.5% of females reporting no physical activity. The finding of a strong protective association between physical activity and risk for NLSAs is consistent with other research on the mental health benefits of physical activity.1 Given the strength of the overall association, the lack of dose–response relationships for the intensity, frequency, and duration of physical activity is surprising. A possible explanation is that even low levels of physical activity may be associated with reduced risk for suicide attempts. While higher frequency, duration, or intensity of physical activity have been associated with increased health benefits in many areas, the dose–response relationship is not uniformly evident.27,28 The overall protective effect for involvement in any physical activity is quite robust even after adjusting for Am J Prev Med 2004;27(4)
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Table 2. Crude and adjusteda ORs for nearly lethal suicide attempts by measures of physical activity Variable (n) Any PA past month Yes (510) No (156) Intensity of primary PA Vigorous (144) Moderate (126) Light (234) None (156) Frequency per week ⱖ5 times (144) 3–4 times (180) 1–2 times (184) None (156) Minutes per usual episode ⱖ61 minutes (174) 31–60 minutes (183) 5–30 minutes (152) None (156) MET minutes/weekb ⬎1260 (162) 420 to 1260 (204) ⬍420 (137) None (156)
% Attempters
Crude OR
95% CI
Adjusted OR
95% CI
14.5 50.6
1.00 6.05
(4.06–9.01)
1.00 5.27
(2.89–9.62)
12.2 15.4 16.1 50.6
1.00 1.30 1.38 7.35
(0.64–2.66) (0.79–2.41) (4.33–12.49)
1.00 0.93 1.37 6.06
(0.36–2.41) (0.63–2.98) (2.83–12.95)
23.6 11.7 10.3 50.6
1.00 0.43 0.37 3.32
(0.24–0.78) (0.20–0.67) (2.02–5.45)
1.00 0.35 0.25 2.44
(0.15–0.78) (0.10–0.63) (1.15–5.14)
17.2 14.2 11.8 50.6
1.00 0.80 0.65 4.93
(0.45–1.41) (0.34–1.21) (2.98–8.15)
1.00 0.97 1.01 5.23
(0.44–2.15) (0.42–2.43) (2.44–11.19)
17.9 12.8 13.1 50.6
1.00 0.67 0.69 4.71
(0.38–1.19) (0.37–1.31) (2.83–7.83)
1.00 1.03 0.65 4.84
(0.48–2.23) (0.26–1.64) (2.28–10.26)
CI, confidence interval; MET, metabolic equivalent; PA, physical activity. a Each indicator of physical activity was examined separately after adjusting for gender, age, race/ethnicity, depression, hopelessness, alcoholism, body mass index, social support, and presence of a serious medical condition. b Using the MET value for walking of 3.5, the cut-points of 420 and 1260 MET minutes correspond to approximately 2 and 6 hours of walking, respectively.
the full set of potential explanatory variables, which suggests that the association between inactivity and NLSA is neither confounded nor mediated by any of these variables. Specifically, the lower risk for NLSAs among those who are active cannot be attributed solely to a tendency for those who are experiencing depression, hopelessness, a serious medical condition, symptoms of alcoholism, or those with an elevated BMI or lack of social support to be less physically active. Nor can it be attributed to the effect of physical activity on these factors, which, in turn, affect suicide attempts. Therefore, the results do not provide clear evidence for a potential mechanism or process through which physical activity is inversely associated with suicide risk. Other physiologic or mental health benefits from physical activity that were not included in the current study might explain the association observed. For example, the complex physiologic interactions of hypothalamic, metabolic, and hormonal changes associated with physical activity may explain the associations observed. Regarding mental health benefits, lower levels of tension, stress, or anxiety, and improved cognitive functioning, self-efficacy, and sense of well-being have been observed among those who are physically active.2,29 To the extent that these factors are associated with risk for an NLSA, they may account for the protective effect observed. There are at least five limitations of this study. First, the measures of physical activity relied on 314
respondents’ reports and may be subject to recall error. Second, questions about intensity, frequency, and duration of physical activity are limited to the one activity that participants engaged in the most. Thus, the measure of whether respondents participate in any physical activity is likely to be more accurate than the measures of intensity, frequency, or duration. Third, although several of the most plausible confounders were included in the study, it is possible that other physical, psychological, or social factors not included in the study may be confounding the association. Fourth, the sample was limited to adolescents and young adults aged 13 to 34 years. It is unclear whether the protective association observed would remain significant among older adults. However, other research on the mental health benefits of physical activity has shown that the benefits remain for older adults.30 Finally, the study ended in September 1995, so the relationships reported in this paper reflect what was happening at that time. However, we know of no reasons why the association observed between physical activity and NLSAs would have changed in the intervening years. In summary, the results indicate a strong protective association between physical activity and NLSAs that was not substantially affected by controlling for sociodemographic characteristics, depression, hopelessness, presence of a serious medical condition, alcoholism, BMI, or social support. Additional re-
American Journal of Preventive Medicine, Volume 27, Number 4
What This Study Adds . . . This study builds on what is known about the mental health benefits associated with being physically active by examining how survivors of nearly lethal suicide attempts differ from community controls on involvement in physical activity. We found significantly lower levels of physical activity among the suicide attempters even after controlling for possible explanatory factors, including depression and alcoholism. The results provide further support for the public health recommendation of regular participation in physical activity.
search is needed to eliminate the possibility that the relationship between physical activity and risk for NLSAs is confounded by other factors, and to explain the process through which the association occurs. Although the evidence supporting a protective effect of physical activity against suicide remains limited, the recommendation of regular participation in moderate physical activity is easily justified by its salubrious effects on other physical and mental health problems. We wish to thank the members of the Houston Case-Control Study of Nearly Lethal Suicide Attempts team for their contributions to the conceptualization, design, and collection of these data.
References 1. U.S. Department of Health and Human Services. Physical activity and health: a report of the Surgeon General. Atlanta GA: U.S. Department of Health and Human Service, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, 1996. 2. Ferron C, Narring F. Sport activity in adolescence: associations with health perceptions and experimental behaviors. Health Educ Res 1999;14:225–53. 3. Oler MJ, Mainous AG, Martin CA, et al. Depression, suicidal ideation, and substance use among adolescents. Are athletes at less risk? Arch Fam Med 1994;3:781–5. 4. Unger JB. Physical activity, participation in team sports, and risk of suicidal behavior in adolescents. Am J Health Promotion 1997;12:90 –3. 5. Brown DR, Blanton CJ. Physical activity, sports participation, and suicidal behavior among college students. Med Sci Sports Exerc 2002;34:1087–96. 6. Paffenbarger RS, Lee IM, Leung R. Physical activity and personal characteristics associated with depression and suicide in American college men. Acta Psychiatr Scand 1994;377(suppl):16 –22.
7. Oswalt R. Finkelberg S. College depression: causes, duration, and coping. Psychol Rep 1995;77:858. 8. Page RM, Tucker LA. Psychosocial discomfort and exercise frequency: an epidemiological study of adolescents. Adolescence 1994;29:183–91. 9. Conboy JK. The effects of exercise withdrawal on mood states in runners. J Sport Behav 1994;17:188 –203. 10. Mondin GW, Morgan WP, Piering PN, et al. Psychological consequences of exercise deprivation in habitual exercisers. Med Sci Sports Exerc 1996; 28:1199 –203. 11. Lane AM, Lovejoy DJ. The effects of exercise on mood changes: The moderating effect of depressed mood. J Sports Med Phys Fitness 2001;41: 539 – 45. 12. Palmer JA, Palmer LK, Michiels K, Thigpen B. Effects of type of exercise on depression in recovering substance abusers. Percept Mot Skills 1995;80: 523–30. 13. Singh NA, Clements KM, Singh MA. The efficacy of exercise as a long-term antidepressant in elderly subjects: a randomized, controlled trial. J Gerontol A Biol Sci Med Sci 2001;56A:497–504. 14. Petajan JH, Gappmaier E, White AT, et al. Impact of aerobic training on fitness and quality of life in multiple sclerosis. Ann Neurol 1996;34:432– 41. 15. Martinsen EW. Physical activity and depression: clinical experience. Acta Psychiatr Scand 1994;89(suppl 377):23–7. 16. Potter LB, Kresnow M, Powell KE, et al. Identification of nearly fatal suicide attempts: self-inflicted injury severity form. Suicide Life Threat Behav 1998;28:174 – 86. 17. Ruuskanen JM, Parkatti T. Physical activity and related factors among nursing home residents. J Am Geriatr Soc 1994;42:987–91. 18. Ikeda RM, Kresnow MJ, Mercy JA, et al. Medical conditions and nearly lethal suicide attempts. Suicide Life Threat Behav 2001;32:60 –7. 19. Kresnow M, Ikeda R, Mercy J, et al. An unmatched case– control study of nearly lethal suicide attempts in Houston, Texas: research methods and measurements. Suicide Life Threat Behav 2001;32:7–20. 20. Ainsworth BE. The compendium of physical activities tracking guide. Columbia SC: Prevention Research Center, Norman J. Arnold School of Public Health, University of South Carolina, January 2002. Available at: http:// prevention.sph.sc.edu/Tools/Compendium_tracking.pdf. Accessed November 14, 2003. 21. Talbot LA, Morell CH, Metter EJ, Fleg JL. Comparison of cardiorespiratory fitness versus leisure time physical activity as predictors of coronary events in men aged ⱕ65 years and ⱖ65 years. Am J Cardiol 2002;89:1187–92. 22. Radloff L. The CES-D Scale: a self-report depression scale for research in the general population. Appl Psychol Measurement 1977;1:385– 401. 23. Beck A, Weissman A, Lester D, Trexler L. The measurement of pessimism: the Hopelessness Scale. J Consult Clin Psychol 1974;42:861–5. 24. Beck A, Weishaar M. Suicide risk assessment and prediction. Crisis 1990;11:22–30. 25. Pillay A, Wassenaar D. Family dynamics, hopelessness, and psychiatric disturbance in parasuicidal adolescents. Aust N Z J Psychiatry 1997;31: 227–31. 26. Powell KE, Kresnow MJ, Mercy JA, et al. Alcohol consumption and nearly lethal suicide attempts. Suicide Life Threat Behav 2001;32:30 – 41. 27. Haskell WL. J.B. Wolffe Memorial Lecture. Health consequences of physical activity: understanding and challenges regarding dose–response. Med Sci Sports Exerc 1994;26:649 – 60. 28. Dunn AL, Trivedi MH, O’Neal HA. Physical activity dose–response effects on outcomes of depression and anxiety. Med Sci Sports Exerc 2001; 33:S587–97. 29. Brandon JE, Loftin JM. Relationship of fitness to depression, state and trait anxiety, internal health locus of control, and self-control. Percept Mot Skills 1991;73:563– 8. 30. Arent SM, Landers DM, Etnier JL. The effects of exercise on mood in older adults: a meta analytic review. J Aging Physical Activity 2000;8:407–30.
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Analyses were conducted on data collected between November 1992 and July 1995 for a population-based, case– control study of nearly lethal suicide attempts among people aged 13 to 34 years. Logistic regression analyses were used to test the association between suicide attempts and physical activity, including the intensity, frequency, and duration of activity, while controlling for demographic factors and potential explanatory variables, such as depression, alcoholism, and the presence of a serious medical condition.
Results:
Suicide attempters were far less likely than controls to report involvement in physical activity in the past month (48% vs 85%, respectively). Intensity, frequency, and duration of activity did not affect this association. The association persisted after adjusting for demographics and potential explanatory variables.
Conclusions: Additional research is needed to explain the process through which the association occurs. The strong protective association observed is consistent with other research on the mental health benefits of physical activity and recommendations of involvement in regular physical activity. (Am J Prev Med 2004;27(4):310 –315) © 2004 American Journal of Preventive Medicine
Introduction
T
he physical health benefits associated with an active lifestyle are extensive, including improvements in the cardiovascular, musculoskeletal, metabolic, endocrine, and immune systems.1 Substantial research suggests that involvement in physical activity may provide mental health benefits as well, such as lower levels of depression and hopelessness. These effects on mood suggest a possible protective association between physical activity and risk for suicide. Relatively few studies have examined the association between physical activity and suicidal behavior directly, and those that have show inconsistent results. For example, several studies of adolescents and young adults have found evidence of inverse associations between sports participation or physical activity and suicidal ideation or behavior, while others have found a protective association for males and no effect, or even From the Division of Violence Prevention, National Center for Injury Prevention and Control, Centers for Disease Control and Prevention (Simon), and Georgia Department of Human Resources, Division of Public Health (Powell), Atlanta, Georgia; and University of Texas– Houston Mental Science Institute (Swann), Houston, Texas Address correspondence and reprint requests to: Thomas Simon, PhD, Mailstop K-60, National Center for Injury Prevention and Control, Centers for Disease Control and Prevention, 4770 Buford Highway, Atlanta GA 30341-3724. E-mail: [email protected]
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higher risk, among more-active females.2–5 These studies included suicide attempters, who are likely to be quite different from those who die from suicide. A prospective longitudinal investigation of the association between physical activity and actual suicides found that the 129 suicide victims in the follow-up sample did not differ on baseline levels of physical activity collected 23 to 27 years earlier.6 The lack of a protective effect for suicide may mean that the effect was not present, that it was not strong enough to be tested with a sample of this size, that the effect is of shorter duration, or that levels of physical activity changed over time. Substantially more evidence is available for an association between involvement in physical activity and mood. For example, people often report using exercise to cope with depressive symptoms.7 Exercise frequency is inversely associated with loneliness, shyness, and hopelessness among adolescents.8 Those who exercise regularly experience an increase in depressive symptoms when their exercise patterns are interrupted.9,10 Moreover, the immediate improvements in mood following exercise appear to be stronger for those who were feeling relatively depressed prior to exercising.11 Experimental studies provide some of the strongest support for the beneficial effect of physical activity on mood. Numerous studies with diverse samples have
Am J Prev Med 2004;27(4) © 2004 American Journal of Preventive Medicine • Published by Elsevier Inc.
0749-3797/04/$–see front matter doi:10.1016/j.amepre.2004.07.003
shown that people who are exposed to an intervention that increases their level of physical activity report lower levels of depression.12–14 A review of exercise intervention studies concluded that aerobic exercise is more effective than a control condition and not significantly different from other intervention strategies in the treatment of unipolar depressive disorders.15 These findings suggest a plausible mechanism for a protective influence of physical activity on the risk for suicidal behavior. To the extent that those who are physically active experience a more positive affect, it is possible that they would be at lower risk for suicidal behavior. This study examined the association between nearly lethal suicide attempts (NLSAs) and involvement in physical activity, including the intensity, frequency, and usual duration of activity among adolescents and young people aged 13 to 34 years. This study is intended to extend earlier research on the association between physical activity and suicide risk in at least two important ways. First, case– control methodology was used to examine those who survived an NLSA. These attempters either used highly lethal methods or they had injuries that were likely to be fatal had they not received emergency medical intervention, and therefore they are more like people who actually die from suicide than people who make less-lethal suicide attempts.16 This methodology permitted a comparison of recent levels of physical activity among nearly lethal attempters to the levels reported by a sample of community controls. Second, the potential explanatory role of indicators of mental health status, such as depressive symptoms, hopelessness, and social support, as well as indicators of poor health status, was examined. Poor physical health is associated with an inability to exercise and risk for suicidal behavior.17,18 Therefore, it is important to control for factors that may indicate poor health status, such as alcoholism, obesity, and recognized medical illness, when testing the association between involvement in physical activity and suicide risk.
Methods Sample This analysis uses data from a population-based, case– control study of NLSAs occurring within a defined catchment area of Houston, Texas. A more detailed description of the sample and procedures is available elsewhere.19 The sample consisted of 153 case and 513 control subjects interviewed from November 1992 through September 1995. Participation in the study was limited to youths and young adults aged 13 to 34 years residing in the central area of Houston, circumscribed by a major highway (Beltway 8).
Case Identification During the study period, an evaluating psychiatric physician completed a form indicating the method and severity of injury for all suicide attempters presenting at the three major
trauma centers serving the Houston population. These three hospitals were selected because they capture the vast majority of the NLSAs within Houston.19 The form, described in detail elsewhere, has been shown to provide a reliable assessment of the medical severity of the attempt.16 In an NLSA, the attempter was likely to have died from suicide had they not received emergency medical or surgical intervention, or the attempter unequivocally employed a method with a high case–fatality ratio (e.g., gunshot wounds and hanging) and sustained an injury, regardless of severity. Of the 1648 suicide attempters meeting the time period, age, and residency requirements, 244 (15%) met the criteria for an NLSA. Among these 244 eligible attempters, 153 (63%) were interviewed, 54 (22%) refused, 22 (9%) denied attempting suicide, 4 (2%) were too ill to be interviewed, and 11 (5%) were lost to follow-up. Patients who agreed to be in the study did not differ from eligible patients who declined on age, gender, or race. The study participants were less likely to be Hispanic and were more likely to have ingested poisons or pills and less likely to have used a firearm than nonparticipants.19
Control Identification Control subjects from the catchment area were enlisted via a random-digit-dial telephone survey during the same time period in which case subjects were enrolled. Control subjects were contacted and screened for age and residence eligibility (13 to 34 years of age, residence within Beltway 8). Of the 4875 telephone numbers contacted, 857 (18%) produced an eligible control subject; 2890 (59%) had no resident within the age range; 1033 (21%) refused to be screened; and 93 (2%) resided outside Beltway 8. Of the 857 eligible control subjects, 513 (60%) completed the in-person interview; 230 (27%) refused to participate when first contacted by telephone; 53 (6%) refused an interview in the field; and 61 (7%) failed to complete the field interview for some other reason (e.g., could not be located, did not appear for interview). The control subjects were similar to the population of Harris County aged 13 to 34 with respect to gender, age, and race/ethnicity.19 To ensure seasonal comparability, potential control subjects were contacted during the same time period in which case subjects were enrolled.
Procedures Case interviews. Case subjects were interviewed after permission was obtained from the responsible physician and the patient (and patient’s guardian, if a minor). Over 75% of participants were interviewed within 7 days of their attempt, and all interviews were completed within 33 days. Seventyeight percent of cases were interviewed in the hospital, 12% at home, and 10% at other locations. Administration of the case interview required an average 44 minutes. Control interviews. Control subjects were interviewed at the home (61%) or workplace (11%) of the subject or at a public location (28%) such as a library or restaurant, depending on the subject’s preference. The average length of the control interview was 37 minutes. Each case and control subject was paid $15 for his or her time upon completing the interview.
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Measures Physical activity. Four questions were used to assess recent physical activity. First, subjects were asked whether they participated in “any physical activities or exercises such as running, calisthenics, golf, gardening, or walking for exercise” in the month before the suicide attempt (or interview for the control subjects). Respondents were then asked to report the type of activity that they spent “the most time doing” during the month, the amount of time they usually spent doing this activity, and the number of times per week they took part in this activity during that month. The primary physical activity was assigned a metabolic equivalent (MET) value based on an established classification and coded as vigorous (MET value ⬎6.0, such as running); moderate (MET value between 4 and 6, such as dancing); or light (MET value ⬍4, such as walking).20,21 The total MET minutes per week were calculated by multiplying the MET value by the number of days and number of minutes that the respondent usually took part in this activity. For ease of interpretation, four categories of MET minutes were created (⬎1260 MET minutes, 420 to 1260 MET minutes, ⬍420 MET minutes, and none). Using the MET value of 3.5 for walking as a reference, the cut-points of 420 and 1260 MET minutes correspond to approximately 2 and 6 hours of walking, respectively. Potential confounders. Respondents provided their gender, age, and race/ethnicity. The Center for Epidemiologic Studies Depression Scale (CES-D) was used to assess depressive symptoms. The 20-item CES-D has been shown to have adequate test–retest reliability and a high degree of internal consistency.22 Participants with CES-D scores ⬎15 were considered depressed. Feelings of hopelessness about the future were assessed with the 20-item true–false Beck Hopelessness Scale. A dichotomous hopelessness variable was created, with scores ⬎8 coded as hopeless.23 This scale has shown high internal consistency, and a strong agreement with clinical ratings of hopelessness.24,25 In the current sample, respondents were asked to report whether they experienced symptoms of depression and hopelessness during the week before the suicide attempt (or the week before the interview, for control subjects). Both measures were found to have a high degree of internal consistency (Cronbach’s alpha was 0.93 for depressive symptoms and 0.87 for hopelessness). A modified version of the Veterans Alcoholism Screening Test was used to detect symptoms of alcoholism within the past year.26 Respondents also were asked if they have “any serious medical problems or conditions.”18 Body mass index (BMI) was calculated using respondents’ self-reports of height and weight. The distribution of BMI scores among controls was used to categorize individuals’ BMI as low (i.e., lowest 25%), medium (i.e., middle 50%) or high (i.e., highest 25%). Reports of having discussed health or emotional problems with a friend or family member in the past 30 days (coded as yes or no) was included as a proxy indicator of social support.
Analysis A series of multivariable logistic regression analyses was used to test the relevant associations. The first model tested the extent to which the demographic characteristics of gender, age, and race/ethnicity, as well as the six potential confounders— depression, hopelessness, alcoholism, the presence of a
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serious medical condition, body mass index, and use of social support—were independently associated with involvement in physical activity. The second model simultaneously tested the extent to which the same demographic characteristics and potential confounders were independently associated with risk for an NLSA. Separate logistic regression models were then analyzed to test the associations between NLSAs and any physical activity in the past month, as well as intensity, frequency, duration, and MET minutes of activity per week. Each physical activity variable was tested separately, first alone and then after adjusting for the demographic characteristics of gender, age, and race/ethnicity, and all six potential explanatory variables. Two-way interaction terms for gender and depression were included in the adjusted models for each measure of physical activity to test whether results varied by gender or depressive symptom status.
Results Involvement in Physical Activity While 85% of the control participants reported engaging in physical activity in the past month, fewer than half (i.e., 48%) of the nearly lethal attempters reported being physically active in the month before their suicide attempt. Overall, involvement in physical activity was significantly more likely among males and those who had used social support (Table 1). Older participants and those who reported symptoms of depression or hopelessness were significantly less likely to report involvement in physical activity.
Predictors of Nearly Lethal Suicide Attempts NLSAs were significantly more common in males than females, and in Hispanics than non-Hispanic whites. These attempts were also significantly more likely among those who reported symptoms of depression, hopelessness, and alcoholism, and those who reported having a serious medical condition. The only potential explanatory factors examined that were not significantly associated with risk for a NLSA were BMI and the use of social support.
Association Between Physical Activity and Nearly Lethal Suicide Attempts Crude and adjusted odds ratios for each of the physical activity variables were calculated next. None of the interaction terms for gender or depression by physical activity was statistically significant. Therefore, only the main effect terms were retained in the model. Even after adjusting for the full set of potential confounders, risk for NLSAs was five times higher among those who had not been physically active in the past month (Table 2). Those who were physically active were at lower risk than those who were not, regardless of the intensity, frequency, or usual duration of their primary physical activity. Relative to those who were active five or more times per week, those who were inactive were at signif-
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Table 1. AORsa for participation in physical activity and nearly lethal suicide attempts by demographic characteristics and potential confounders Physically active Characteristics of the entire sample Gender Female (362) Male (304) Age 13–18 (188) 19–34 (478) Race/ethnicity Hispanic (149) NH Black (173) NH White (327) Depressed No (370) Yes (294) Hopeless No (516) Yes (145) Alcoholism No (527) Yes (121) Medical condition No (557) Yes (109) Body mass index Low (169) Medium (330) High (160) Social support used No (347) Yes (319)
Attempters
%
AOR
(95% CI)
%
AOR
(95% CI)
73.5 80.3
1.00 1.79
(1.16–2.76)
19.3 27.3
1.00 1.79
(1.03–3.10)
83.5 73.9
1.00 0.46
(0.28–0.77)
25.0 22.2
1.00 0.65
(0.37–1.16)
72.5 71.7 81.0
1.00 1.06 1.62
(0.61–1.83) (0.97–2.70)
30.2 31.8 15.3
1.00 1.02 0.27
(0.52–2.00) (0.14–0.53)
86.2 64.3
1.00 0.41
(0.25–0.69)
6.0 44.6
1.00 3.08
(1.61–5.87)
82.4 57.2
1.00 0.48
(0.28–0.80)
9.1 70.3
1.00 17.51
(9.27–33.08)
78.9 66.1
1.00 0.74
(0.45–1.24)
18.6 43.0
1.00 2.13
(1.15–3.94)
78.1 68.8
1.00 0.82
(0.48–1.39)
19.0 43.1
1.00 2.61
(1.37–5.00)
75.7 79.7 70.6
1.00 1.41 0.94
(0.86–2.32) (0.54–1.64)
24.9 23.0 20.6
1.00 1.51 0.88
(0.79–2.88) (0.41–1.87)
74.9 78.4
1.00 1.54
(1.01–2.33)
22.5 23.5
1.00 0.77
(0.45–1.31)
AOR, adjusted odds ratio; CI, confidence interval. a The results are from a simultaneous multivariable logistic regression model that included all the variables listed in the table.
icantly greater risk, and those who were less frequently active (i.e., one to two or three to four times per week) were at lower risk. However, the overall indicator of physical activity, MET minutes per week, showed no difference across the levels of MET minutes among those who were active. Those in the highest level of MET minutes per week were at significantly lower risk for NLSAs than those who were inactive.
Discussion The results indicate that the likelihood of an NLSA was substantially higher among those who reported no physical activity in the past month. This association remained after adjusting for demographic characteristics and potential confounders, including depression, hopelessness, alcoholism, presence of a serious medical condition, BMI, and social support. However, no dose– response to intensity, frequency, or duration, either alone or when combined as MET minutes per week, was observed. Estimates of physical inactivity from a nationally representative sample of young U.S. adults suggest that the control subjects were similar to the national
average. The results from the 1992 National Behavioral Risk Factor Surveillance System indicated that 18.9% of males and 25.4% of females aged 18 to 29 reported no participation in leisure-time physical activity.1 The subset of control subjects recruited for the current study who were aged 18 to 29 had comparable levels of inactivity, with 15.0% of males and 25.5% of females reporting no physical activity. The finding of a strong protective association between physical activity and risk for NLSAs is consistent with other research on the mental health benefits of physical activity.1 Given the strength of the overall association, the lack of dose–response relationships for the intensity, frequency, and duration of physical activity is surprising. A possible explanation is that even low levels of physical activity may be associated with reduced risk for suicide attempts. While higher frequency, duration, or intensity of physical activity have been associated with increased health benefits in many areas, the dose–response relationship is not uniformly evident.27,28 The overall protective effect for involvement in any physical activity is quite robust even after adjusting for Am J Prev Med 2004;27(4)
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Table 2. Crude and adjusteda ORs for nearly lethal suicide attempts by measures of physical activity Variable (n) Any PA past month Yes (510) No (156) Intensity of primary PA Vigorous (144) Moderate (126) Light (234) None (156) Frequency per week ⱖ5 times (144) 3–4 times (180) 1–2 times (184) None (156) Minutes per usual episode ⱖ61 minutes (174) 31–60 minutes (183) 5–30 minutes (152) None (156) MET minutes/weekb ⬎1260 (162) 420 to 1260 (204) ⬍420 (137) None (156)
% Attempters
Crude OR
95% CI
Adjusted OR
95% CI
14.5 50.6
1.00 6.05
(4.06–9.01)
1.00 5.27
(2.89–9.62)
12.2 15.4 16.1 50.6
1.00 1.30 1.38 7.35
(0.64–2.66) (0.79–2.41) (4.33–12.49)
1.00 0.93 1.37 6.06
(0.36–2.41) (0.63–2.98) (2.83–12.95)
23.6 11.7 10.3 50.6
1.00 0.43 0.37 3.32
(0.24–0.78) (0.20–0.67) (2.02–5.45)
1.00 0.35 0.25 2.44
(0.15–0.78) (0.10–0.63) (1.15–5.14)
17.2 14.2 11.8 50.6
1.00 0.80 0.65 4.93
(0.45–1.41) (0.34–1.21) (2.98–8.15)
1.00 0.97 1.01 5.23
(0.44–2.15) (0.42–2.43) (2.44–11.19)
17.9 12.8 13.1 50.6
1.00 0.67 0.69 4.71
(0.38–1.19) (0.37–1.31) (2.83–7.83)
1.00 1.03 0.65 4.84
(0.48–2.23) (0.26–1.64) (2.28–10.26)
CI, confidence interval; MET, metabolic equivalent; PA, physical activity. a Each indicator of physical activity was examined separately after adjusting for gender, age, race/ethnicity, depression, hopelessness, alcoholism, body mass index, social support, and presence of a serious medical condition. b Using the MET value for walking of 3.5, the cut-points of 420 and 1260 MET minutes correspond to approximately 2 and 6 hours of walking, respectively.
the full set of potential explanatory variables, which suggests that the association between inactivity and NLSA is neither confounded nor mediated by any of these variables. Specifically, the lower risk for NLSAs among those who are active cannot be attributed solely to a tendency for those who are experiencing depression, hopelessness, a serious medical condition, symptoms of alcoholism, or those with an elevated BMI or lack of social support to be less physically active. Nor can it be attributed to the effect of physical activity on these factors, which, in turn, affect suicide attempts. Therefore, the results do not provide clear evidence for a potential mechanism or process through which physical activity is inversely associated with suicide risk. Other physiologic or mental health benefits from physical activity that were not included in the current study might explain the association observed. For example, the complex physiologic interactions of hypothalamic, metabolic, and hormonal changes associated with physical activity may explain the associations observed. Regarding mental health benefits, lower levels of tension, stress, or anxiety, and improved cognitive functioning, self-efficacy, and sense of well-being have been observed among those who are physically active.2,29 To the extent that these factors are associated with risk for an NLSA, they may account for the protective effect observed. There are at least five limitations of this study. First, the measures of physical activity relied on 314
respondents’ reports and may be subject to recall error. Second, questions about intensity, frequency, and duration of physical activity are limited to the one activity that participants engaged in the most. Thus, the measure of whether respondents participate in any physical activity is likely to be more accurate than the measures of intensity, frequency, or duration. Third, although several of the most plausible confounders were included in the study, it is possible that other physical, psychological, or social factors not included in the study may be confounding the association. Fourth, the sample was limited to adolescents and young adults aged 13 to 34 years. It is unclear whether the protective association observed would remain significant among older adults. However, other research on the mental health benefits of physical activity has shown that the benefits remain for older adults.30 Finally, the study ended in September 1995, so the relationships reported in this paper reflect what was happening at that time. However, we know of no reasons why the association observed between physical activity and NLSAs would have changed in the intervening years. In summary, the results indicate a strong protective association between physical activity and NLSAs that was not substantially affected by controlling for sociodemographic characteristics, depression, hopelessness, presence of a serious medical condition, alcoholism, BMI, or social support. Additional re-
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What This Study Adds . . . This study builds on what is known about the mental health benefits associated with being physically active by examining how survivors of nearly lethal suicide attempts differ from community controls on involvement in physical activity. We found significantly lower levels of physical activity among the suicide attempters even after controlling for possible explanatory factors, including depression and alcoholism. The results provide further support for the public health recommendation of regular participation in physical activity.
search is needed to eliminate the possibility that the relationship between physical activity and risk for NLSAs is confounded by other factors, and to explain the process through which the association occurs. Although the evidence supporting a protective effect of physical activity against suicide remains limited, the recommendation of regular participation in moderate physical activity is easily justified by its salubrious effects on other physical and mental health problems. We wish to thank the members of the Houston Case-Control Study of Nearly Lethal Suicide Attempts team for their contributions to the conceptualization, design, and collection of these data.
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