Prospective association between obesity and depression: evidence from the Alameda County Study

OBJECTIVE: To examine the temporal relation between obesity and depression to determine if each constitutes a risk factor for the other. DESIGN: A two-wave, 5-y-observational study with all measures at both times. SUBJECTS: A total of 2123 subjects, 50 y of age and older, who participated in the 1994 and 1999 waves of the Alameda County Study. MEASUREMENTS: Obesity defined as body mass index (BMI) greater than or equal to 30. Depression assessed using DSM-IV symptom criteria for major depressive episodes. Covariates include indicators of age, gender, education, marital status, social support, life events, physical health problems, and functional limitations. RESULTS: Obesity at baseline was associated with increased risk of depression 5 y later, even after controlling for depression at baseline and an array of covariates. The reverse was not true; depression did not increase the risk of future obesity. CONCLUSION: These results, the first ever on reciprocal effects between obesity and depression, add to a growing body of evidence concerning the adverse effects of obesity on mental health. More studies are needed on the relation between obesity and mental health and implications for prevention and treatment.