Depression often occurs with other medical disorders. The evidence supporting the overlap is especially strong with cardiovascular disorders. Recently I wrote about the example of hypertension and a research study showing that an integrated treatment program addressing both mood and blood pressure resulted in greater improvements in both high blood pressure and depression.

The very common type 2 form of diabetes, also called adult-onset diabetes, is another example of a disorder associated with depression. Research has shown that people with this type of diabetes are more likely to suffer with depression compared to similar people without diabetes. The opposite also is true — people who have been diagnosed with depression are more likely to have type 2 diabetes than are similar people without depression.

Which came first, the depression or the diabetes? That's an important question because the answer could have implications about the causes of both these disorders and might provide important insights regarding treatment.

According to a study recently published in the Journal of the American Medical Association, the answer to the question is "both." Researchers examined data from approximately 5,000 people ages 45 to 84 years for just over 3 years. Individuals were identified as depressed if they scored high on a depression scale or were treated with an antidepressant medication.

Fasting glucose levels were classed as normal, impaired, or high enough to represent diabetes type 2. The people in the highest glucose group or those already treated for diabetes were classed in the diabetes group.

The study showed that over the approximate 3-year follow-up period, the people who initially were treated for type 2 diabetes had a 54 percent increase in their risk of developing depressive symptoms compared to those not treated for diabetes. The analysis also showed that people starting off with depressive symptoms ultimately had a 42 percent greater likelihood of developing diabetes.

The take-home message is simple. People with diabetes should be screened to see whether they have depressive symptoms that should be treated. People with depression should be evaluated to determine whether they have any evidence of diabetes. Treating both conditions could make a big difference for patients.