Researchers followed more than 4,000 British civil servants for almost two decades in one of the longest studies ever to examine the impact of mental health on obesity.
People with symptoms of one or more mental disorders three times during the study were twice as likely to be obese at the final screening as people who never reported such symptoms.
“We started with people who were not obese,” study researcher Mika Kivimaki, PhD, of the University College London, tells WebMD. “The more times mental health symptoms were reported, the greater the risk for becoming obese by the end of the study. This points to a dose-response association between mental disorders and weight gain.”
Obesity and Depression
The study included 4,363 government workers between the ages of 35 and 55 when enrolled in the mid- to late-1980s.
Mental health and physical examinations were conducted at study entry and at three other time points over an average follow- up of 19 years. The physical exams included measurements of weight, height, and body mass index (BMI).
After adjusting for known risk factors for obesity, such as the use of psychiatric drugs associated with weight gain, people who had symptoms of depression, anxiety, or other mental health problems at the start of the study were more likely than those who did not to become obese over time.
But obesity did not significantly increase the risk for depression, anxiety, or other mental health disorders, as other studies have shown.
The study appears in the journal BMJ Online First.
“When we looked at it the other way around and asked if weight gain leads to mental illness, the association was not clear,” Kivimaki says. “That doesn’t mean there is no association, but it appeared to be much weaker in our study.”
Which Comes First?
“There are very plausible reasons why depression could increase the risk for obesity and very plausible reasons why obesity could increase the risk for depression,” he says. “I think it is likely that both of these things are happening.”
Simon’s own study, published in 2006, suggested the association runs in both directions.
He points out that the obesity rate among the U.S. population is in the 25% to 30% range, while the rate of obesity among people with significant depression is twice that.
“Obesity is the norm with depression, so it is pretty hard to separate the two,” he says. “It is akin to saying that people who are depressed have more marital problems and people with more marital problems have more depression. You would need a pretty sharp knife to separate the two.”