Depression and obesity: do shared genes explain the relationship?

Abstract

Background: Studies have found a modest association between depression and obesity, especially in women. Given the substantial genetic contribution to both depression and obesity, we sought to determine whether shared genetic influences are responsible for the association between these two conditions.

Methods: Data were obtained from 712 monozygotic and 281 dizygotic female twin pairs who are members of the community-based University of Washington Twin Registry. The presence of depression was determined by self-report of doctor-diagnosed depression. Obesity was defined as body mass index of > or =30 kg/m(2), based on self-reported height and weight. Generalized estimating regression models were used to assess the age-adjusted association between depression and obesity. Univariate and bivariate structural equation models estimated the components of variance attributable to genetic and environmental influences.

Results: We found a modest phenotypic association between depression and obesity (odds ratio=1.6, 95% confidence interval=1.2-2.1). Additive genetic effects contributed substantially to depression (57%) and obesity (81%). The best-fitting bivariate model indicated that 12% of the genetic component of depression is shared with obesity.

Conclusions: The association between depression and obesity in women may be in part due to shared genetic risk for both conditions. Future studies should examine the genetic, environmental, social, and cultural mechanisms underlying the relationship between this association.

Figure 1

Path diagram depicting additive genetic effects shared by depression and obesity plus additive genetic (A), common environmental (C), and unique environmental (E) effects unique to each trait. The parameter estimates and 95% confidence intervals are path coefficients, indicating the relative importance of the latent variables A, C, and E to depression and obesity.