There is a reciprocal association over time between depression and obesity, Dr. Floriana S. Luppino, of Leiden University Medical Center, the Netherlands, told Reuters Health by email.
Obesity, Luppino and colleagues found, increases the risk of depression in initially non-depressed individuals by 55 percent and depression increases the risk of obesity in initially normal-weight individuals by 58 percent.
Luppino said the analysis was not designed to determine a given person's risk of depression, only to figure out how much obesity increased that risk. However, for comparison, a recent study funded by the National Institute of Mental Health found that nearly one out of four cases of obesity is associated with a mood or anxiety disorder.
These findings, the NIMH notes on its website, appear to support what other studies have found - that obesity, which is on the increase in the US - is associated with increasing rates of depression and other mental health problems.
The new findings stem from pooled data from 15 published studies that looked at whether being overweight or obese is associated with depression, and vice versa.
The studies, which collectively involved more than 58,000 people, used body mass index, or BMI, to gauge how fat or thin a person is. For reference, a US adult with a BMI of 25 or more is considered overweight, while one with a BMI of 30 and above is considered obese.
Being obese, Luppino told Reuters Health, not only increases the risk of depression, but is more likely to fuel the onset of clinical depression, rather than merely depressive symptoms.
In contrast to obesity, the association between depression and being overweight (but not obese) did not run the other way, Luppino noted. Being overweight increased the risk of depression in initially non-depressed individuals somewhat, but depression did not increase the risk of being overweight over time.
The findings, reported in the latest issue of the Archives of General Psychiatry, also suggest that the link between obesity and later depression is more pronounced among Americans than among Europeans.
Why? A dose-response association -- meaning the higher the BMI, the more people get depressed -- might explain the association, Luppino said. And the average American weighs more than the average European.
However, the effect of the psychological distress should not be neglected, the researcher said. Overweight and obesity, can induce low self-esteem and body dissatisfaction, Luppino explained, especially in Western countries where thinness is often considered a beauty ideal. Both low self-esteem and body dissatisfaction are known to increase the risk of depression.
Because both depression and obesity carry major health implications, it is very important to try to prevent and treat both, Luppino said.
The Dutch team encourages doctors and other health professionals, working in different fields, to collaborate and exchange their expertise. Doctors treating patients who are overweight or obese could screen their patients for depression and vice versa -- psychiatrists or general doctors encountering depressed patients could suggest their overweight patients see a dietitian, Luppino suggests.