Diabetes itself doesn't up risk of depression

NEW YORK (Reuters Health) - Although people with diabetes have a higher risk of being diagnosed with depression than other people, a large new study has found that much of that increase can be accounted for by their more frequent contacts with the medical system, rather than the diabetes itself.

"Our results are consistent with the hypothesis that having a diagnosed chronic condition increases the frequency of a depression diagnosis," write Dr. Patrick J. O'Connor of HealthPartners Research Foundation in Bloomington, Minnesota, and his colleagues. "Our data suggest, however, that patients with diabetes are no more affected by this susceptibility than patients with other chronic conditions who have frequent outpatient visits."

Previous research had suggested a higher likelihood of being depressed among diabetic individuals, O'Connor and his team write in their report, while other studies have had mixed results. One analysis of 42 studies found that people with diabetes were twice as likely to have depression than non-diabetics, they point out in the Annals of Family Medicine.

But few studies of the issue have accounted for the number of primary care visits that patients make, O'Connor and his team add, which could influence both whether or not a person had diabetes and whether they were diagnosed with and treated for depression.

To investigate, the researchers looked at records from a large medical group that treated about 225,000 patients between 1997 and 2003. They compared 2,932 people who received a diagnosis of diabetes during that time and 14,144 diagnosed with diabetes before 1997 to two different control groups. The first was matched by age and sex, while the second group was matched by age, sex and number of primary care visits.

For every group of patients, the likelihood of being newly diagnosed with depression fell as the number of times they visited the doctor increased. Among patients who already had diabetes, those who had few physician visits during the study period were 46% more likely to be newly diagnosed with depression during the course of the study.

But for the diabetic patients who had more than 10 physician visits during the study period, the risk of a new depression diagnosis was similar to that of non-diabetic individuals who visited their physicians equally often.

The reason why people -- diabetic or not -- who visit the doctor less often are more likely to be depressed isn't clear, the researchers say. "These data might indicate that primary care clinicians are good at recognizing depression after only a few visits," they write. "Other explanations are possible, however; perhaps physician who do not recognize depression early are not likely to diagnose it later."

SOURCE: Annals of Family Medicine, July/August 2009.