weight bmi scale — Image: Tsuji/Istock.com via AFP Relaxnews

New research has found more evidence to suggest that body mass index (BMI) is linked to depression, with a BMI over 30 associated with a higher risk of the condition.

Carried out by researchers at the University of South Australia and the University of Exeter, United Kingdom, the new study looked at data from more than 48,000 people with depression participating in UK Biobank, a large, long-term study which includes genomic data on U.K. residents aged between 37 and 73 years of age.

The researchers also looked at data on more than 290,000 people born between 1938 and 1971 who acted as a control group.

Using the genomic data, they then analyzed the genes associated with higher BMI, but with a lower risk of diseases like diabetes, to see whether obesity-related health problems such as diabetes caused depression.

The findings, published in the International Journal of Epidemiology, showed that the genes associated with high BMI and a low risk of disease were just as strongly associated with depression as the genes associated with higher BMI and diabetes, suggesting that it is the psychological impact of being overweight, rather than obesity-related illnesses that cause depression.

The association was also stronger for women than for men.

Obesity is classified as a BMI greater than 30 kilograms per meter squared, with BMI calculated by dividing your weight in kilograms by your height, in meters squared.

The researchers also found that very thin men with a low BMI are also more likely to have depression than men of normal weight or very thin women.

“The current global obesity epidemic is very concerning,” said Prof. Elina Hypponen, who co-led the study. “Alongside depression, the two are estimated to cost the global community trillions of dollars each year.”

“Our research shows that being overweight doesn’t just increase the risks of chronic diseases such as cancer and cardiovascular disease; it can also lead to depression,” she added.

The study is not the first to find a link between BMI and depression, with a 2016 study also finding that women with a BMI of 30 to 34.9 have double the risk of depression compared with women of normal weight, while researchers from Brigham & Women’s Hospital in Boston, United States, presented findings last year which suggested women with a higher BMI were also at an increased risk of postpartum depression.

Dutch research presented at the European Congress on Obesity in 2017 also suggested that children who were overweight at age 8 or 13 had more than triple the risk of developing major depression at some point later in life. JB

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