Summary

The link between diabetes and depression is real. A new study shows that people with depression are more likely to develop diabetes. And treated (but not untreated) diabetes is linked to an increased risk of depression. Therefore, treatment of depression could prevent diabetes. Equally, those who have diabetes need to be aware of the risk of depression.

Introduction

Clinical depression, and depressive symptoms, are more common among those with diabetes than among the rest of the population. This might be because diabetes predisposes people for depression or vice-versa - or perhaps a mixture of both. As both depression and diabetes are serious chronic conditions, it is important to try to understand the relationship between them. Researchers at Johns Hopkins University, Baltimore, Maryland, have tried to clarify the link with a new investigation derived from the Multi-Ethnic Study of Atherosclerosis.

What was done

The study involved nearly 7,000 men and women aged between 45 and 84 years enrolled between 2000 and 2002 and followed up to 2004 or 2005. Depressive symptoms were measured with a standard questionnaire and diabetes status was assessed from blood glucose measurement and whether medication was being taken. The participants were categorized as having normal fasting glucose, impaired fasting glucose or type 2 diabetes. The researchers then carried out two analyses - one to see if depression is a risk factor for diabetes, and the other to test whether diabetes is a risk factor for depression.

What was found

In the first analysis, the risk of diabetes was found to be higher among those with depressive symptoms. The way the researchers put it is that the incidence of type 2 diabetes was 22 per 1,000 person years for those who were depressed and 16.6 cases per 1,000 person years for those who were not depressed. In the second analysis, those who had treated type 2 diabetes were 52 percent more likely to develop depression than those without diabetes. Surprisingly, perhaps, untreated diabetics did not have a higher risk of depression compared to the general population.

What this study means

The researchers suggest that depression could raise the risk of type 2 diabetes through lifestyle factors. That is, those with depression are more likely to be obese and physically inactive which would both increase the risk of diabetes. Depression also alters the body's biochemistry - making inflammation more likely which could also predispose to diabetes. They also put forward the idea that being treated for diabetes might itself be stressful, with regular doctor or hospital appointments and maybe self-monitoring commitments. This might be why treated diabetics are at greater risk while those who are untreated are not. What to do? First of all, if depression is treated, it could reduce the risk of diabetes developing at all. And second, doctors treating people with type 2 diabetes - and the patients themselves - should be aware that depression might develop and should be treated promptly.