Summary: A new study finds that obesity can substantially increase the risk of depression, even when other obesity-related illnesses are not present.
Source: University of South Australia.
Researchers from the University of South Australia and the University of Exeter report the strongest evidence to date that excess body weight itself contributes to the development of depression, independent of accompanying physical illnesses.
A study published in the International Journal of Epidemiology used genetic and medical data to untangle whether the link between obesity and depression is driven by physical disease or by the psychological consequences of excess weight. The researchers conclude that the psychological burden of being overweight is an important driver of depression risk, not simply the presence of diabetes or other obesity-related conditions.
The analysis drew on UK Biobank data, comparing more than 48,000 people identified with depression to a control group of over 290,000 participants. These individuals, born between 1938 and 1971, contributed both medical records and genetic information that allowed the team to apply a genomic approach to the question.
Depression status was determined using a combination of hospital records and participant self-reports. The genomic strategy focused on sets of genes that are associated with higher body mass index (BMI), and then separated those genes into subgroups: genes that increase BMI while also increasing risk of metabolic diseases, and genes that raise BMI but are not linked to higher risk of conditions such as diabetes.
Professor Elina Hypponen, Director of the Australian Centre for Precision Health at the University of South Australia and co-leader of the study, explains that this design allowed the team to isolate the psychological component of excess weight. “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,” Prof Hypponen says. “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.”
Gender differences emerged in the findings. The study observed that women with higher BMI-related genetic risk showed a clearer association with depression. At the lower end of the BMI scale, very thin men were found to have a higher likelihood of depression compared with men of normal weight and compared with very thin women.
Professor Hypponen emphasizes the public health implications: “The current global obesity epidemic is very concerning. 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.”
The study’s approach—leveraging genetic variants that decouple higher BMI from metabolic disease—strengthens the argument that the psychosocial effects of excess weight are a direct contributor to mental health burden. While the biological consequences of obesity remain critically important to address, these results highlight that interventions should also consider social, psychological and behavioral supports to mitigate the mental health impact of living with overweight or obesity.
The UK Biobank is a large-scale biomedical database that recruited around 500,000 individuals aged 37 to 73 years across the United Kingdom between 2006 and 2010. The resource includes medical histories, lifestyle information and genetic data for participants, enabling large population-level studies of disease risk and the genetic contributors to health outcomes.
*Obesity is defined here using body mass index (BMI). Individuals classified as obese have a BMI greater than 30 kg/m². BMI is calculated by dividing a person’s weight in kilograms by their height in metres squared.
Source: Candy Gibson – University of South Australia
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Original Research: The study appears in the International Journal of Epidemiology.