Previous studies have found connections between diabetes and depression, but it was not clear if one caused the other or if the correlation was formed of factors that merely happened to be held in common. A study by Dr. Sherita Golden, published this week in the Journal of the American Medical Association, helps to clarify this issue by taking before and after evaluations of different groups while correcting for confounding factors.

Dr. Golden gathered three groups of patients, those with diabetes II but without elevated depressive symptoms according to the CES-D scale, those with elevated depressive symptoms but without diabetes, and a control group without either illness. These groups were then evaluated four years later to determine whether the presence of one illness could predict the development of the other.

Subjects with depressive symptoms were 1.1 times more likely to develop diabetes even with corrections for socio-economic and metabolic factors. This challenges suspicions that depression only leads to diabetes because of lower levels of physical activity coupled with poor diet. However, when all lifestyle differences were corrected for, the risk increase lost its statistical significance. The authors of the study state that they do not believe that lifestyle can explain all of the risk, but will have to wait for future studies to prove that with statistical validity. 

The results from the group starting with diabetes were even harder to analyze. Subjects who were being treated for diabetes were almost twice as likely to have elevated depressive symptoms. This would be a simple and compelling warning if it weren’t for the finding that subjects with subclinical diabetes or full-blown but untreated diabetes were actually less likely to develop depressive symptoms. The authors speculated that knowing that you have diabetes can be emotionally damaging, but no truly satisfactory explanation for this unexpected lowering of risk was offered.

Clearly, more research must be done to clarify the nature of the connection between depression and diabetes. Right now, all doctors can be sure of from studies such as these is that if depression or diabetes are detected in a patient, it would be wise to check for the other illness as well.