Experts funded by the charity Diabetes UK have found a causal relationship and shared genetics suggesting depression may actually cause type 2 diabetes.
More than 95% of the 422 million people worldwide with diabetes have type 2 diabetes, and until now, researchers have known that people with type 2 diabetes are around twice as likely to suffer depression compared with those without diabetes and that people with depression have a higher risk of developing type 2.
However, it has been unclear whether depression caused type 2, or vice versa, or whether other factors are at play.
In the latest study, researchers used a statistical method called Mendelian randomisation to analyse genetic and health information.
They found, for the first time, that depression directly causes an increased risk of developing type 2 diabetes, but not that diabetes causes depression.
The study 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 those of normal weight.
The researchers also noted seven genetic variants that contribute to both type 2 diabetes and depression.
These shared genes play a role in insulin secretion or inflammation in the brain, pancreas or fat tissue, with changes in these biological processes potentially explaining how depression increases type 2, they suggested.
While a direct cause was not found for diabetes causing depression, experts still believe that the burden of living with type 2 diabetes can be a factor in developing depression.
“This hugely important study gives us new insights into the links between genetics, type 2 diabetes and depression, indicating that depression can contribute to the development of type 2 diabetes,” Dr Elizabeth Robertson, director of research at Diabetes UK, said.
“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,” she said.
The study, published in the journal Diabetes Care, used data from hundreds of thousands of people in the UK and Finland, including 19,344 people with type 2 diabetes, more than 5,000 people diagnosed with depression and 153,079 who self-reported depression.
