New evidence points to a link between obesity and depression, even in the absence of additional health problems. The findings stem from a large scale genomic analysis which suggests the psychological impact of being overweight causes depression rather than associated illnesses such as diabetes.
Researchers from the University of South Australia and University of Exeter in the U.K. reviewed data from the U.K. Biobank, targeting more than 48,000 people with depression. Scientists then compared medical and genetic information from a control group of more than 290,000 people born between 1938 and 1971. Hospital data and self-reporting were used to determine whether people had depression.
The research, published in the International Journal of Epidemiology, shows that the psychological impact of being overweight causes depression. Individuals are categorized as being obese if they have a body mass index (BMI) greater than 30 kg/m². BMI is calculated by dividing weight in kilograms by height, in meters squared.
Director of the Australian Centre for Precision Health, UniSA Professor Elina Hypponen, who co-led the study, said the team used a genetic research approach to explore the causal link between the two conditions.
Investigators separated out the psychological component of obesity from the impact of obesity-related health problems, using genes associated with higher BMI but lower risk of diseases like diabetes.
These genes were just as strongly associated with depression as those genes associated with higher BMI and diabetes. This suggests that higher BMI causes depression both with and without related health issues. This effect was stronger in women than in men.
“We separated the psychological component of obesity from the impact of obesity-related health problems using genes associated with higher body mass index (BMI), but with lower risk of diseases like diabetes,” Hypponen said.
“These genes were just as strongly associated with depression as those genes associated with higher BMI and diabetes. This suggests that being overweight causes depression both with and without related health issues, particularly in women.”
Dr. Jess Tyrrell, of the University of Exeter Medical School, said, “Obesity and depression are both global health problems that have a major impact on lives and are costly to health services.
“We’ve long known there’s a link between the two, yet it’s unclear whether obesity causes depression or vice-versa, and also whether it’s being overweight in itself or the associated health problems that can cause depression,” she said.
“Our robust genetic analysis concludes that the psychological impact of being obese is likely to cause depression. This is important to help target efforts to reduce depression, which makes it much harder for people to adopt healthy lifestyle habits.”
Researchers tested their results in a second large-scale cohort, using data from the Psychiatric Genomics Consortium. They reached the same conclusion, verifying their results.
At the other ends of the BMI spectrum, very thin men are more prone to depression that either men of normal weight or very thin women.
“The current global obesity epidemic is very concerning,” Hypponen said. “Alongside depression, the two are estimated to cost the global community trillions of dollars each year.