Bidirectional association between weight change and depression in mid-aged women: a population-based longitudinal study

BACKGROUND: There is some evidence for a bidirectional association between obesity and depression. However, studies examining weight change and depression are scarce and report inconsistent findings. OBJECTIVE: The objective was to investigate the relationship between average annual percentage weight change and depression in mid-aged women. DESIGN: This was a prospective cohort study. SUBJECTS: A total of 8246 women aged 45-50 years at baseline participating in the Australian Longitudinal Study on Women's Health were surveyed every 3 years over a 12-year period. Information on body mass index and depression was collected at each survey. We used regression models to investigate the effect of weight change predicting depression and vice versa, by calculating odds ratios (ORs) with 95% confidence intervals (CIs). RESULTS: Weight gain was associated with an increased risk of prevalence (OR 1.39, 95% CI 1.25-1.56) and incidence (OR 1.30, 95% CI 1.14-1.49) of depression. However, in time-lagged analyses, where weight change between the two preceding surveys was used to predict incidence of depression at the current survey, no statistically significant associations with depression were found. Compared with women without depression, women with prevalent and incident depression had an increased risk of weight gain (OR 1.29, 95% CI 1.19-1.40 and OR 1.20, 95% CI 1.05-1.38, respectively). When incidence of depression was lagged with respect to weight change between the two subsequent surveys, depression remained associated with an increased risk (OR 1.19, 95% CI 1.00-1.41) of gaining weight. CONCLUSION: These findings suggest that depression may cause weight gain over the next 3 years, but that weight change (loss or gain) may not lead to depression. Further research at shorter intervals, perhaps 6 monthly or yearly is needed to ascertain whether weight change is an independent predictor of depression in the shorter term.