Department of Social and Preventive Medicine, Laval University, Québec, G1V 2M2, Canada. Department of Nutrition, Harvard School of Public Health, MA 02115, USA.
Background: Lifestyle determinants, such as nutrition, physical activity and smoking, are potential risk factors for mental health. However, studies that analyzed prospectively their relationship with depression and suicide risk are scarce.
Methods: We accessed data among three large-scale prospective cohorts of U.S. men and women, Nurses' Health Study (NHS, n=121,700 in 1976), NHSII (n=116,671 in 1989), and Health Professionals' Follow-up Study (HPFS, n=51,529 men in 1986). We analyzed the relationship between nutritional factors (omega-3 fatty acids, coffee/caffeine, dietary profiles), physical activity/inactivity (TV-watching), and smoking with depression and suicide risk. Participants in all cohorts were followed with biennial questionnaires on lifestyle (including diet every 4 years), medication use, and disease incidence. Depression was defined as reported both physicians-diagnosed depression and antidepressant use. Among the three cohorts, deaths from suicide were determined by physician review of death certificates. Multivariate adjusted relative risks (RRs) were estimated with Cox proportional hazard models. Cohort specific RRs were pooled for suicide using random-effect models.
Results: During follow-up, we documented 2,607 incident cases of depression in NHS and 277 deaths from suicide in the three cohorts. Physical activity was associated with lower risk of depression among NHS, whereas increasing TV-watching time was associated with an increased risk. Our results do not support association between dietary “Prudent” (high in vegetables) and “Western pattern” and depression risk. In contrast, inflammatory dietary pattern (derived from reduced-rank regression) was associated with a higher depression risk (RR comparing extreme quintiles = 1.41; 95% CI: 1.22–1.63). Omega-3 failed to show protective effects on depression and suicide risk. Caffeinated coffee intake was associated with a decrease risk of depression and suicide. Comparing extreme categories of caffeinated coffee intakes (≥4 cups/day vs. ≤1 cup/week), RR (95% CI) was 0.80 (0.64–0.99) for depression and 0.47 (0.27–0.81) for suicide. Decaffeinated coffee was not associated with depression or suicide risk. Compared to never smokers, the pooled multivariate RR (95% CI) of suicide was 1.15 (0.91–1.45) for former smokers and 2.69 (2.11–3.42) for current smokers.
Conclusions: Results from these three large cohorts support associations between lifestyle determinants and risk of depression and suicide. Further investigations are needed to confirm these findings and to address potential explanatory paths by which these risk factors impact mental health.