Depression may play a direct role in the development of type 2 diabetes, according to research that experts say could help boost efforts to prevent the disease.
Researchers have found a causal link and shared genetics that suggest depression may be a cause of type 2 diabetes, a disease that affects more than 500 million people worldwide.
The discovery has prompted calls for depression to be considered a risk factor for type 2 diabetes, alongside other risk factors such as obesity, physical inactivity and a family history of the condition.
The researchers suggest that people with a history of depression should be assessed for their risk of type 2 diabetes so that they can be supported to avoid developing the condition.
Experts have known for years that people with type 2 diabetes are about twice as likely to suffer from depression than those without the condition. It is also known that people with depression have a higher risk of developing type 2 diabetes.
However, it has been unclear whether depression causes type 2, or vice versa, or whether other factors are involved. In the latest study, researchers found for the first time that depression directly causes an increased risk of developing type 2, but did not find that diabetes causes depression. The findings are published in the journal Diabetes Care.
Dr Elizabeth Robertson, Director of Research at Diabetes UK, which funded the study, said: “This hugely important study gives us new insights into the links between genetics, type 2 diabetes and depression, and suggests that depression may contribute to the development of type 2 diabetes. Type 2 diabetes is complex, with many risk factors – and previous research has shown that the condition is more common in people with depression.
“This study gives us a better understanding of why, and suggests that depression should now be considered a risk factor for type 2 diabetes. This knowledge could help healthcare professionals to improve care and support for people with a history of depression and prevent more cases of type 2 diabetes.”
The study used data from hundreds of thousands of people in the UK and Finland, including 19,000 people with type 2, 5,000 diagnosed with depression and 153,000 who self-reported depression.
The researchers used a statistical method called Mendelian randomisation to analyse genetic and health information. They found that only 36.5% of the effect of depression on type 2 diabetes could be explained by obesity. Obese people are significantly more likely to have type 2 diabetes than people of a healthy weight.
The researchers also identified seven genetic variants that contribute to both type 2 diabetes and depression. These common genes play a role in insulin secretion or inflammation in the brain, pancreas or fat tissue, and changes in these biological processes may explain how depression increases type 2, they suggested.
And while a direct cause for diabetes causing depression has not been found, experts believe that the burden of living with type 2 diabetes may be a factor in developing depression.
“We strongly encourage anyone with depression to know their risk of type 2 diabetes by completing Diabetes UK’s free online Know Your Risk tool, so they can get the right support to reduce their risk and avoid type 2 diabetes,” said Robertson.
Professor Inga Prokopenko from the University of Surrey, who led the study, said: “Our discovery sheds light on depression as a contributing cause of type 2 diabetes and could help improve prevention efforts.
“The findings are important both for people living with the condition and for healthcare providers, who should consider additional screening to prevent the onset of type 2 diabetes in people with depression.”
