Obesity is associated with a 25 percent increase in the risk of developing mood and anxiety disorders and a 25 percent decrease in likeliness for substance abuse, according to a paper in the July issue of Archives of General Psychiatry, one of the JAMA/Archives journals.

About 31 percent of all U.S. adults were obese in 2000, an increase from 23 percent in 1990, according to background information in the article. Obese adults are at higher risk of diabetes, cardiovascular disease and other harmful conditions. Previous studies have suggested a link between obesity and depression, but little research has examined the associations between obesity and other psychiatric disorders.

Gregory E. Simon, M.D., M.P.H., of the Group Health Cooperative, Seattle, and colleagues studied 9,125 adults from across the country who were interviewed as part of a large national survey of mental disorders between Feb. 5, 2001, and Feb. 12, 2003. Participants (average age 44.8 years) completed an in-home interview that included questions about demographic characteristics, height, weight and psychiatric disorders.

These included mood disorders, such as major depression, dysthymia (persistent mild depression with associated symptoms) and bipolar disorder; anxiety disorders, such as panic disorder and generalized anxiety disorder; and substance abuse disorders, including alcohol or drug dependence.

Of all the participants, 6,795 had a body mass index (BMI) of less than 30 and 2,330 had a BMI of 30 or greater and were therefore considered obese. Those who were obese had a higher prevalence of mood and anxiety disorders and a lower prevalence of substance abuse disorders over their lifetimes. These associations remained similar for men and women. The link between obesity and mood disorders appeared strongest in non-Hispanic whites and in those with higher education levels.

“The estimated prevalence of lifetime mood disorder in those with BMIs below 30 and in those with BMIs 30 or higher translates to a population-attributable risk of 24 percent, which indicates that nearly one-quarter of the cases of obesity in the general population are attributable to the association with mood disorder,” the authors write. “This calculation illustrates the public health importance of the association but does not indicate a direction for the causal relationship. It is equally correct to state that more than one-fifth of cases of mood disorder in the general population are attributable to the association with obesity.” Increased appetite, weight gain, reduced physical activity and binge eating have all been associated with depression, potentially increasing risk for obesity. However, obesity could also contribute to depression by limiting physical activity, or through the stigma that may be associated with being overweight, especially among some women and other particular sociodemographic groups. An unknown third cause also could be linked to both. The results also do not indicate the mechanisms behind the negative association between obesity and substance abuse.

“We conclude that obesity is meaningfully associated with a range of common mood and anxiety disorders in the general U.S. population,” the authors write. “Obesity is associated with a moderately lower risk of substance use disorder. Variation in the obesity-depression relationship by education level and race/ethnicity suggests an important role of social or cultural factors in mediating or moderating the relationship between obesity and mood disorders.”

American Medical Association (AMA)