Adiposity and depression/ anxiety: Interrelationship and mediators

Objectives: To explore the directionality of the association of adiposity with major depressive disorder (MDD) and generalized anxiety disorder (GAD), and to assess the role of inflammation, diet quality and physical activity in this association. Methods: We used data from 2,977 individuals from the 1993 Pelotas Cohort (Brazil) who attended the 18- and 22-year follow-ups. We assessed general obesity using body mass index (BMI) and fat mass index (FMI), and abdominal obesity using waist circumference. MDD and GAD were assessed using the Mini-International Neuropsychiatric Interview. C reactive protein (CRP) and interleukin-6 level (IL-6) were used as a measure of inflammation, diet quality was estimated using the Revised Diet Quality Index, and physical activity level was assessed by the International Physical Activity Questionnaire (IPAQ, min/day). The association between adiposity and MDD/GAD was assessed using logistic regression and the natural indirect effect of mediators was estimated using G-computation. Results: General obesity assessed by BMI (OR: 2.3; 95% CI:1.13; 4.85), FMI (OR: 2.6; 95%CI: 1.37; 4.83), and abdominal obesity (OR: 2.5; 95%CI: 1.18; 5.39) was associated with higher odds of MDD, whereas MDD was only associated with obesity assessed by BMI (OR=1.9; 95% CI: 1.09; 3.46). Obesity and GAD were not associated. CRP, diet quality and physical activity did not mediate the effect of obesity on MDD, and CRP mediated about 25% of the effect of MDD on adiposity. Conclusions: Depression, but not GAD, is associated with adiposity in both directions, with a stronger evidence for the direction obesity-depression. Inflammation explains part of the effect of MDD on obesity but not the other way around. Further research should explore other mechanisms that could be involved in the association between obesity and depression.