A study has suggested that depression could play a direct role in the development of type 2 diabetes.
Previous research has indicated that people with type 2 diabetes are approximately twice as likely to experience depression as those without diabetes. Also, people with depression were found to have a higher risk of developing type 2 diabetes.
However, the authors of a new study, published in the journal Diabetes Care, pointed out that it had remained unclear "if depression caused type 2, or vice versa", or if other factors were responsible for the link between the two conditions.
"Type 2 diabetes is complex, with multiple risk factors – and previous research has shown that the condition is more common in people with depression," explained Dr Elizabeth Robertson, director of research at Diabetes UK, which helped fund the investigation.
Depression Directly Increases Type 2 Diabetes Risk
For the study, led by the University of Surrey, researchers assessed the causal relationships and shared genetics between depression and type 2 diabetes. To do this they used two-sample bi-directional Mendelian randomisation to analyse genetic and health information of 19,344 people with type 2 diabetes, more than 5,000 people diagnosed with depression, and 153,079 who self-reported depression, to determine whether type 2 diabetes and depression could cause the development of the other.
The analysis revealed, for the first time, a "significant causal effect" for depression increasing the risk of developing type 2 diabetes (OR=1.26). Higher bodyweight partly, but not wholly, explained the effects of depression on type 2 diabetes, alerted the authors.
However, they found no evidence of causality in the reverse direction between type 2 diabetes and depression, they stressed.
Having performed mediation analysis, the researchers found that "36.5% of the effect from depression to type 2 diabetes was mediated by BMI".
The researchers further pinpointed seven genetic variants that contribute to both type 2 diabetes and depression. The 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 risk of type 2 diabetes.
The "hugely important" study provided new insights into the links between genetics, type 2 diabetes and depression, highlighted Dr Robertson, who proposed that depression should "now be considered a risk factor" for type 2 diabetes.
Prevention Efforts Helped
People with depression would benefit from a type 2 diabetes risk assessment, suggested the authors, so these people could be supported to avoid developing the condition.
Inga Prokopenko, professor e-One Health and head of statistical multi-omics at the University of Surrey, said that the "discovery illuminates depression as a contributing cause of type 2 diabetes and could help to improve prevention efforts".
Diabetes UK emphasised how it was "vital" that people with diabetes received care and support for both the physical and mental impact the condition can have on health.
The authors highlighted the "importance to prevent type 2 diabetes at the onset of depressive symptoms" and postulated that "anti-depressant treatment offered to people with depression at risk of type 2 diabetes should favour those that provide better glycaemic control such as selective serotonin reuptake inhibitors (SSRIs)".
Dr Robertson 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."