Study shows strong link between obesity and depression

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The study, published in the July issue of the Archives of General Psychiatry, found that an obese person is about 25 percent more likely than a non-obese person to have a mood or anxiety disorder, such as depression. It also indicated that among Caucasian Americans and more educated people who are obese, that likelihood may be as high as 44 percent.

While the study did not show whether obesity leads to depression or vice versa, "it's almost certain that the association works in both directions," said Greg Simon, MD, MPH, a Group Health psychiatrist and the lead author of the study.

The researchers also found a negative association between obesity and substance abuse. That is, an obese person is 25 percent less likely than a non-obese person to have had a substance abuse disorder sometime in their lives.

"Understanding the connection between obesity and depression is an important public health issue because both of these conditions are so common and have a significant impact on our health care systems," Dr. Simon explained.

He pointed to the evidence that an average American has a 30 percent chance of being obese. This study shows that when a person is depressed, the odds of also becoming obese are as high as 40 percent.

About 20 percent of Americans are diagnosed sometime in their lives with depression. "Among those who are obese, that likelihood of depression jumps to 28 percent," said Dr. Simon.

The study is based on an in-person survey that the researchers from Harvard Medical School conducted among a nationally representative sample of 9,125 adult men and women. Obesity is defined in the study as having a body mass index (BMI) of 30 or more.

While previous studies have shown a connection between obesity and depression, this is the largest and most representative study of the two problems in U.S. population. Also, this study included a much more careful assessment of mental health problems than earlier research, according to Dr. Simon.

Unlike many previous studies that show a link between obesity and depression among women only, this study revealed a strong link in both genders. There were significant differences among social and cultural groups. In groups where obesity is more common—that is, among non-white and less educated groups—there is less depression among the people who are obese. But in groups where there is less obesity, it is accompanied by more depression.

This may indicate that stigma accounts for some of the relationship between obesity and depression, said Dr. Simon. "Perhaps in groups where obesity is less socially normative, it's less acceptable and that's why there's a greater association with depression," he suggested. "But in groups where it is less stigmatized, obesity doesn't seem to be as depressing."

Research currently underway Group Health may lead to a better understanding of the link between body weight and mental health, and how these problems might be moderated.

Dr. Simon and his team are now conducting studies to address questions such as: Do depressed people have more difficulty increasing physically activity? Are their diets different than the diets of non-depressed people? Are depressed people less likely to be successful with structured weight-loss programs? Can weight-loss programs designed specifically for depressed people make a difference?

Simon's article was co-authored by Michael Von Korff, ScD, Kathleen Saunders, JD, and Diana Miglioretti, PhD, of Group Health Center for Health Studies; Paul K. Crane, MD, and Gerald van Belle, PhD, of the University of Washington; and Ronald C. Kessler, PhD, of Harvard Medical School.

Group Health Cooperative Center for Health Studies