A baseline questionnaire about medical history and health practices was completed and then repeated every 2 years through 2006. Self-reported symptoms of depression, use of antidepressant medication, and physician-diagnosed depression were used as measures of depression. Depressed mood was assessed using the 5-item Mental Health Index, with a score of 52 or less indicating severe depression.
Those who reported a diagnosis of type 2 diabetes mellitus had the diagnosis confirmed by means of a supplementary questionnaire validated by medical record review.
During the 10-year follow-up, 2844 women were diagnosed as having type 2 diabetes and 7415 developed depression.
The relative risk of developing type 2 diabetes among women who were depressed was 1.17 (95% confidence interval [CI], 1.05 – 1.30). Study participants using antidepressants had a relative risk of 1.25 (95% CI, 1.10 – 1.41).
After controlling for all covariates, the investigators found women with diabetes had a relative risk of 1.29 (95% CI, 1.18 – 1.40) of developing clinical depression.
In addition, the relative risk for depression in diabetic subjects taking no diabetic medication, oral hypoglycemic agents, and insulin was 1.25 (95% CI, 1.09 – 1.42), 1.24 (95% CI, 1.09 – 1.41), and 1.53 (95% CI, 1.26 – 1.85), respectively.
The results also showed that compared with their nondiabetic counterparts, women with diabetes were more likely to have a higher body mass index and less likely to be physically active, a finding that suggests these 2 risk factors could be “major mediating factors.”
Nevertheless, they note the association remained significant after controlling for body mass index and lifestyle factors, which suggests “depression has effects on incident diabetes independent of adiposity and inactivity.”
The finding that women taking antidepressant medications were at higher risk of developing type 2 diabetes compared with those with severe depressive symptoms or physician-diagnosed depression has at least 2 possible explanations — antidepressant medications may be a marker of more severe, chronic, or recurrent depression or the medications themselves may increase diabetes risk.
“Although antidepressant medication use might be a marker of severe depression, its specific association with elevated risk of diabetes warrants further scrutiny,” they write.
In addition, the study authors note that these findings reinforce the hypothesis that diabetes may be related to stress: “Depression may result from the biochemical changes directly caused by diabetes or its treatment, or from the stresses and strains associated with living with diabetes and its often debilitating consequences.”
“This large, well-established cohort study provides evidence that the association between depression and diabetes is bidirectional and this association is partially explained by, but independent of, other known risk factors such as adiposity and lifestyle variables. Future studies are needed to confirm our findings in different populations and to investigate the potential mechanisms underlying this association,” the investigators conclude.
The study was funded by the National Institutes of Health and the National Alliance for Research on Schizophrenia and Depression. The study authors have disclosed no relevant financial relationships.
Arch Intern Med. 2010;170:1884-1891.More