Depression and diabetes are two common conditions that do not resemble each other but appear to be inextricably linked. Type II diabetes, the variation largely blamed on poor lifestyle and dietary practices, has long been linked to mood disorders - affected subjects are twice as likely to suffer depression as the general population. Is this because diabetes fosters depression, or can depression actually cause diabetes?

A new study confirms and elaborates on the two-way cause and effect relationship between the two conditions. Certain behavioral triggers (obesity, social isolation, lack of exercise) have been known to cause both depression and diabetes, but limited research left the academic community unable to definitively explain these shared factors. It now appears that depression's influence on diabetes risks is considerably greater than diabetes' ability to induce depression.

The study involved 55 subjects enrolled in diabetes prevention programs who bore symptoms of “pre-diabetes” (they were overwhelmingly obese and female and their lifestyles were accordingly sedentary). After administering a standard depression survey, researchers determined that at least 1 in 3 subjects were depressed, also noting that 20% of the group was on some sort of antidepressant treatment regimen when the study began. Researchers continued to survey subjects throughout the study to determine their respective levels of depression, finding a directly inverse relationship between depression and diabetes' primary symptom, insulin resistance - as depression improved, subjects grew less sensitive to insulin. This held true even after researchers controlled for all related lifestyle variables.

What caused this change? The most likely suspect remains the stress hormone cortisol, a major byproduct of the anxiety common to depressive subjects. Excessive amounts of cortisol slow blood sugar metabolism and render the body more sensitive to insulin, so the abnormally high presence of cortisol in the blood of depressed subjects understandably heightens their pre-existing diabetic symptoms. Medication can all but eliminate this change: the insulin levels of depressed, medicated subjects mirrored those of standard, non-depressed diabetics.  We can’t yet say that antidepressants relieve the diabetic symptoms of affected individuals. But we can state with certainty that depression is more common among diabetics and that any individuals with a family history of diabetes should be particularly sensitive to signs of depression – it will intensify their symptoms if left unchecked.