Study strengthens evidence of link between obesity and depression

A large Australian-UK study has found the strongest evidence to date that obesity causes depression.

The study, published in the International Journal of Epidemiology, isolated the genetic variants associated with obesity from the existence of other weight-related conditions – such as diabetes – to determine obesity alone is likely a risk factor for the mental health condition.

The study found women may be more vulnerable to the adverse mental health consequences of obesity.Credit:Stocksy

While previous studies have supported a causal association between obesity and depression, researchers from the University of South Australia and the University of Exeter in the UK examined the effect of the genetic variants known to cause obesity on mental health.

Researchers used genetic data from the UK Biobank, a resource of human biological data from 500,000 volunteer participants aged between 37 and 73 years, to compare the prevalence of these genetic variants with rates of self-reported and hospital-recorded depression.

"The strength of our study design is its ability to focus on the effects of high BMI, rather than any dietary or societal influences which would typically be associated with obesity," said the University of South Australia's Dr Elina Hypponen, who co-led the study.

"We approximated high BMI and obesity using genetic proxy markers which are inherited at birth, and which do not themselves lead to or change in response to poor diet."

The team used genetic data from more than 48,000 people who had self-reported as having depression (defined as having seen a GP, psychologist or been admitted to hospital for anxiety or depression, as well as having experienced symptoms for minimum of two weeks), comparing them with a control group of more than 290,000 people.

Professor Hypponen said the researchers "separated the psychological component of obesity" by analysing the prevalence of genes which were associated with higher BMIs, but not other weight-related health conditions, such as diabetes, as well as those associated with higher BMIs and weight-related conditions.

“These genes were just as strongly associated with depression as those genes associated with higher BMI and diabetes," Professor Hypponen said.

This suggests that being overweight causes depression both with and without related health issues.

"This suggests that being overweight causes depression both with and without related health issues.”

Obese women were more likely to report depression than obese men, a result in line with research the team had done on older obese people, published earlier this year.

Professor Hypponen said the findings "suggest the stigma of high BMI differs between men and women".

According to 2014-15 data from the Australian Institute of Health and Welfare, 4.9 million Australians are obese, defined as having a BMI over 30, totalling roughly 28 per cent of the population.

Obesity has been identified as a major risk factor for a number of physical health conditions, including cardiovascular disease and Type 2 diabetes.

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