March 4, 2010 — Obesity and depression are closely linked in that each raises the risk for the other, a new meta-analysis confirms.
The study found that obese people have a 55% increased risk of developing depression, and those with depression have a 58% increased risk of becoming overweight over time.
These results should spur medical specialties to collaborate in an effort to prevent depression and obesity, each a condition that poses major health problems, said lead author Floriana S. Luppino, MD, Leiden University Medical Center, The Netherlands.
"The first step is to try to do the best we can, based on the facts we know now, and that would be for psychiatrists to monitor their patients’ weight and for internal medicine or general practitioners who see obese or overweight patients to check on their mental state to see if they’re on the way to developing a mood disorder which is mostly treatable."
The study is published in the March issue of Archives of General Psychiatry.
For the analysis, researchers searched the literature for studies published in English up to March 2008. The studies had to have a follow-up period of at least 1 year, express weight as body mass index (BMI), and specify the way depression was assessed. The final analysis included 15 studies.
For the examination of the link between overweight (defined as a BMI between 25 and 29.99) or obesity (defined as a BMI of 30 or more) and depression, the total number of subjects was 55,387. For the inverse relationship, there were 7196 subjects. Some studies provided longitudinal data on both directions.
The pooled odds ratio (OR) was 1.55 (95% confidence interval [CI], 1.22 – 1.98; P < .001) for the 8 studies that examined the association between obesity at baseline and depression at follow-up.
Obesity and Depression Link Stronger in the United States?
The ORs for American studies differed significantly from European ones (P = .05), indicating that the association was stronger among Americans. The reason for this is not clear. However, according to the World Health Organization, the mean adult BMI is higher in the United States than in Europe. "If the mean BMI is higher in the US, and a higher BMI means more depression, that could explain it," said Dr. Luppino.
A significant difference was also seen between ORs for depression outcome as a clinical diagnosis and as depressive symptoms (P = .05), suggesting that the effect of the association is stronger when depression is assessed by a diagnostic clinical interview rather than a self-report symptom list.
As for the inverse relationship — depression causing obesity — the pooled OR of the 9 studies examining the effect of depression on obesity was 1.58 (95% CI, 1.33 – 1.87; P < .001). Subgroup analysis did not show any significant differences.
The pooled OR for depression exposure on overweight was 1.20 (95% CI, 0.87 – 1.66; P = .26). Subgroup analysis found the association stronger with longer follow-up.
The stronger relationship between depression and obesity compared with that between depression and overweight suggests there is a "dose-response" element to the association, said Dr. Luppino.
Psychiatrists Should Monitor Weight
These new data suggest that psychiatrists should regularly monitor the weight of their depressed patients, something that is "easy to do," said Dr. Luppino.
"If you think a patient is borderline overweight or obese, maybe there could be some kind of intervention, for example, sending that patient to a dietitian or someone involved in internal medicine, or to a general practitioner. This may help that patient take control, possibly preventing weight gain with lifestyle changes or dietary changes."
Although previous research suggests that the relationship between depression and excess weight only applies to women, this study confirms it also exists in men.
The relatively long period of follow-up for the studies included in the analysis may be 1 possible explanation.
"In a short period of time, their different hormones could explain why women are more prone to becoming overweight or obese, but in time, other pathways may become involved, and this might explain why, in the end, the risk of obesity or overweight [in depressed patients] exists in both genders,” said Dr. Luppino.
The relationship between depression and obesity is likely multifactorial, involving more than 1 pathway — biological, psychological or both, she said.
Biological pathways could involve inflammation (linked to both depression and obesity), the hypothalamic-pituitary-adrenal axis (also linked to both conditions), and/or insulin resistance (obesity increases risks for diabetes and insulin resistance, which could induce alterations in the brain and increase the risk for depression).
Emphasis on Thinness
One psychological pathway could originate with Western society’s emphasis on thinness, with weight gain contributing to decreased self-esteem, a risk factor for depression, said Dr. Luppino.
The nature of the relationship between obesity and depression may vary from person to person. "For one person, it might be a biological system that’s not working the way it should, but in another person, it could be that self-esteem is low, and if that person is obese, it might be the last push for that person to get depressed."
But perhaps elements of both a biological pathway and a psychological pathway are needed to create the obesity-depression link. "If one gets obese or overweight due to biological factors but self-esteem is great and you don’t have body dissatisfaction, you may not get depressed," said Dr. Luppino.
Genes that increase vulnerability to depression can also play a role, said Dr. Luppino. "For a person with good self-esteem who is overweight or obese but who is not prone to depression, my best guess is that the chances for being depressed at the end are lower."
Other explanatory factors could include unhealthy lifestyles, such as lack of physical activity and poor diet, and the use of antidepressants, all of which can lead to weight gain.
Future research should examine such things as the potential role of depression characteristics, medication use, physical activity, and dietary patterns, the study authors write.
Excellent Example
Reached for a comment, Michelle Riba, MD, associate chair for Integrated Medicine and Psychiatric Services, Department of Psychiatry, University of Michigan, Ann Arbor, and past president, American Psychiatric Association, said the study "is an excellent example of the use of a meta-analytic approach for 2 large public health problems — depression and obesity."
But she did note some limitations of the analysis; for example, it only included adult studies. "We know many of these problems begin much earlier, in childhood, Dr. Riba told Medscape Psychiatry.
As well, important factors, such as sleep and sleep problems related to depression and obesity, and patients with diabetes or cardiovascular diseases were not included.
"We also don’t know about medications that patients might have been on to affect mood and obesity. Bipolar disorder, alcohol and substance abuse, socioeconomic issues, and health insurance are also not addressed," she said.
The authors have disclosed no relevant financial relationships.
Arch Gen Psychiatry. 2010;67:220-229.
