Obesity Linked to Depression, or Vice Versa

SEATTLE, July 5 - Depression and obesity are often partners in pathology, according to investigators here.

Obese persons have a 20% elevated risk of depression compared with those of normal weight, reported Gregory E. Simon, M.D., M.P.H., of the Group Health Cooperative here, and colleagues in the July issue of Archives of General Psychiatry.

For white, college-educated obese individuals, the additional depression risk reaches as high 44%, said Gregory E. Simon, M.D., M.P.H., of the Group Health Cooperative here in the July issue of Archives of General Psychiatry.

Previous studies have linked obesity with depression, but they relied mostly on data from white sample populations. The current study more accurately represents the U.S. population, Dr. Simon and colleagues said.

In addition, most previous studies linked obesity with depression only in women. The current study, with a larger sample size and more statistical power than most previous studies, found the same results for women and men, the investigators said.

The study analyzed data from more than 9,000 individuals who took part in the National Comorbidity Survey Replication, an in-person survey of U.S. residents in the 48 contiguous states conducted from 2001 to 2003.

Obesity was associated with significant increases in lifetime diagnosis of major depression (odds ratio=1.21; 95% confidence interval=1.09 to 1.35), bipolar disorder (OR=1.47; 95% CI=1.12 to 1.93), and panic disorder (OR=1.27; 95% CI=1.01 to 1.60).

Obesity was associated with significantly lower lifetime risk of substance use disorder (OR=0.78; 95% CI=0.65 to 0.93). The investigators did not speculate on the reason.

The study found no difference in the obesity-depression link between men and women, but the association was strongest in whites (OR=1.38; 95% CI=1.20 to 1.59) and college graduates (OR=1.44; 95% CI=1.14 to 1.81).

As to whether depression causes obesity or vice versa, the researchers found evidence for both mechanisms.

For example, increased appetite and weight gain are common symptoms of depression. In addition depressed individuals are less likely to exercise and more likely to binge eat. Finally, some antidepressants may lead to weight gain, the investigators said.

On the other hand, the stigma attached to obesity may lead to depression, the researchers suggested. In addition, obesity or related comorbidities tend to reduce physical activity which can lead to depression by cutting off the sense of reward or pleasure that comes from exercise, they said.

"We have no way of distinguishing the direction of the causal relationship between obesity and psychiatric disorders or the possibility that unmeasured common causes induce an association between them," the researchers said.

As far as the stronger links found with being white and college educated, the investigators said that "Some previous research suggests that self-perception of overweight and the perceived stigma associated with obesity may both be greater in white populations and those with higher income or educational attainment."

"Clarifying the direction of causal relationships will require alternative research designs, including longitudinal and experimental studies," they concluded.