The association between diabetes and depression is bidirectional in middle-age women, with the presence of either disease significantly raising the risk that the other also will develop, a report shows.
Moreover, diabetes raises the risk of depression, and depression raises the risk of diabetes, independently of other known risk factors such as adiposity that are common to both diseases, said An Pan, Ph.D., of Harvard School of Public Health, Boston, and his associates.
To date, "only a few" studies have examined the association between diabetes and depression simultaneously, and their results have been inconsistent. "Therefore, we took advantage of repeated measurements of lifestyle risk factors and disease occurrences during 10 years of follow-up in a large prospective cohort"--the Nurses' Health Study--to address the bidirectional relationship.
The NHS involved female registered nurses residing in 11 states who were followed every 2 years via health questionnaires. Dr. Pan and his colleagues assessed a subset of 65,381 NHS participants who were aged 50-75 years in 1996 and were followed until 2006.
Depressive symptoms were categorized according to the women's scores on the Mental Health Index 5, whether depression had been diagnosed by a physician and whether they used antidepressants. Diabetes was categorized as requiring no medications, only oral hypoglycemic agents, or insulin therapy.
During follow-up, 2,844 incident cases of diabetes were documented. The risk of developing diabetes was significantly higher in women who had depressive symptoms than in those who did not.
In addition, this rise in diabetes risk showed a "dose-response relationship" with worsening depressive symptoms, such that diabetes risk increased significantly as scores on the MHI-5 rose.
This association between depression and diabetes remained significant, although it was markedly attenuated, when the data were adjusted to account for body mass index (BMI) and lifestyle factors, particularly physical activity.
In a separate analysis of the same data, 7,415 study subjects developed incident clinical depression during follow-up. Compared with women who did not have diabetes, women with diabetes had a relative risk of developing clinical depression of 1.44, the investigators said (Arch. Intern. Med. 2010;170:1884-91).
Controlling for major comorbidities such as hypertension and coronary heart disease attenuated this association, but it remained significant.
In addition, the risk of developing clinical depression also showed a dose-response relationship with worsening diabetes symptoms. Women with diabetes who were not taking any medication had a relative risk of 1. …