Depression can play a direct role in the development of type 2 diabetes, according to new research we funded that looked at the cause-and-effect relationship between the two conditions.
The researchers say their findings indicate that people with a history of depression should be assessed for their risk of type 2 diabetes, so they can be supported to avoid developing the condition.
The study, led by Professor Inga Prokopenko from the University of Surrey, used genetic data from hundreds of thousands of people in the UK and Finland to shed new light on the complex relationship between depression and type 2 diabetes.
We know from previous research that people with type 2 diabetes are around twice as likely to experience depression compared to those without diabetes. And we also know that people with depression have a higher risk of developing type 2 diabetes.
But it wasn’t clear if depression caused type 2, or vice versa. Or whether other factors were responsible for the link between the two conditions.
In this latest study, researchers used a statistical method, called Mendelian randomisation, to analyse genetic and health information and determine whether type 2 diabetes and depression can cause the development of the other.
Their analysis revealed for the first time that depression directly causes an increased risk of developing type 2 diabetes. And showed that higher bodyweight partly, but not wholly, explained the effects of depression on type 2 diabetes.
The researchers also pinpointed seven genetic variants that contribute to both type 2 diabetes and depression.
The shared genes play a role in insulin production and in levels of inflammation in the brain, pancreas or fat tissue. These changes the genes bring about inside the body can potentially explain how depression increases risk of type 2 diabetes.
The researchers didn't find any evidence of a cause-and-effect relationship of type 2 diabetes on the development of depression. But there are indirect links between the conditions, with both affected by common risk factors such as obesity and low levels of physical activity.
The demands of living with the relentless day-to-day burden of type 2 diabetes can also be a factor in developing depression.
Dr Elizabeth Robertson, Director of Research at Diabetes UK, said:
Professor Inga Prokopenko, Diabetes UK-funded researcher at the University of Surrey, said:
What do we know about depression and type 1 diabetes?
This study only looked at people with type 2 diabetes. We know that like those living with type 2, people with type 1 diabetes are also more likely to develop depression than people who don't have diabetes.
But depression is not a risk factor for developing type 1 diabetes, which is caused by a problem with the immune system.