Depression may play a direct role in the development of type 2 diabetes

Depression may directly cause an increased risk of developing type 2 diabetes, with scientists identifying seven genetic variants that are involved in both diseases.

The research, published in the journal Diabetes Care, analysed the causal relationship between diabetes and type 2 diabetes using available data from people in the UK and Finland and suggests that people with a history of depression might benefit from having their risk of type 2 diabetes assessed.

Professor Inga Prokopenko, from the University of Surrey, who led the study, said: 'Our discovery illuminates depression as a contributing cause of type 2 diabetes and could help to improve prevention efforts.'

The researchers analysed data from over 19,000 people with type 2 diabetes, over 5000 people diagnosed with depression, as well as over 150,000 people who self-reported depression. They used a statistical method called two-sample bi-directional Mendelian randomisation to establish whether a causal relationship between type 2 diabetes and depression exists in either direction. They found that while depression directly increases the risk of type 2 diabetes, type 2 diabetes does not increase the risk of developing depression. This effect was only partly explained by body weight.

They further analysed genetic data for this cohort and used genome-wide association studies to identify seven genetic variants that contribute to both type 2 diabetes and depression. The affected genes play a role in insulin secretion and inflammation in the brain, pancreas and fat tissue. These changes could potentially explain how depression and type 2 diabetes are linked.

Diabetes affects more than 500 million people worldwide and over five million people in the UK alone – about 90 percent of which are living with type 2 diabetes. Type 2 diabetes and depression share some symptoms and previous research indicated that people with type 2 diabetes are twice as likely to experience depression, while depression is associated with a higher risk of developing type 2 diabetes. Before this current research, it was unclear whether this relationship was based on correlation or causation and which way the relationship might work.

'The findings are important for both individuals living with the conditions and healthcare providers, who should consider implementing additional examinations to help prevent type 2 diabetes onset in people suffering from depression,' explained Professor Prokopenko.

However, other scientists disagree on whether the study should be the basis for a change in clinical practice.

'It is well known that risk of type 2 diabetes is slightly raised among people with depression and vice versa and there are a number of possible reasons why such an association might be observed.' Professor David Curtis, from University College London, said. 'However, I do not think the current study tells us anything definite about the mechanisms involved. Because the effects are fairly small I do not think that doctors need to make any changes in terms of how they deal with people with depression or diabetes.'