A genomic study conducted by the University of Exeter, UK, and the University of South Australia has found that higher body mass index (BMI) has a strong psychological association with depression, including in the absence of other health problems.

The relationship was particularly strong in women, compared to men.

The study used data from the UK BioBank resource; it compared 48,791 people with diabetes, defined by hospital data and self-reporting, to 291,995 controls.

Obesity was defined as having a BMI of more than 30kg/m2.

Researchers separated the psychological impact of obesity and the effect of obesity-related health problems on depression by selecting and testing genes associated with higher BMI and lower risk of related diseases, such as diabetes.

It was found that these genes were as strongly associated with depression as genes linked with both higher BMI and a high risk of diabetes.

Co-leader of the study, director of the Australian Centre for Precision, University of South Australia professor Elina Hypponen said: “We separated the psychological component of obesity from the impact of obesity-related health problems using genes associated with higher BMI, but with 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 being overweight causes depression both with and without related health issues – particularly in women.”

The researchers tested these results in a study of 45,591 depression patients and 97,647 controls from the Psychiatric Genomics Consortium dataset and reached the same conclusion.

The final results were published in the International Journal of Epidemiology.

University of Exeter Medical School lecturer Dr Jess Tyrrell said: “We’ve long known there’s a link between the obesity and depression, 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.

“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.”