Depression and Diabetes in Women: A Bidirectional Association

More than 10% of the adults in the United States have diabetes; in those aged ≥60 years of age, the prevalence is 23%. Approximately 14.8 million Americans aged ≥18 years are affected by major depressive disorder (MDD) in a given year. The lifetime incidence of MDD is estimated as >12% in men and >20% in women. The possible association between MDD and diabetes in middle-aged and elderly women has been observed in several studies, but to date the hypothesis that the diabetes–depression association is bidirectional has been addressed in only a few prospective studies. To address the possible bidirectional relationship of diabetes and depression, researchers recently utilized 10 years of follow-up of repeated measurements of lifestyle risk factors and occurrences of diabetes and depression in a large prospective cohort. They reported study results in Archives of Internal Medicine [2010;170(21):1884-1891]. The data were gathered from the Nurses’ Health Study cohort that was established in 1976 when 121,700 female registered nurses responded to a mailed questionnaire about their medical history and health practices. In 1996 questions regarding clinical depression were asked; the current study used 1996 as a baseline. After applying exclusion criteria, the present analyses included 65,381 women aged 50 to 75 years in 1996 who were observed until 2006. Clinical depression was defined as having diagnosed depression or using antidepressants. Depressed mood was defined as having clinical depression or severe depressive symptoms (Mental Health Index [MHI-5] score of ≤52). Presence of diabetes was self-reported and confirmed with a supplementary questionnaire validated by a review of medical records. At baseline, compared with those with MHI-5 scores of 86 to 100 (referents), women with higher levels of depressive symptoms were more likely to be younger, have no spouse, and smoke cigarettes. They were less likely to consume alcohol and be physically active. Those with depressed mood had higher body mass index (BMI) scores compared with those who were least depressed. There were 2844 incident cases of diabetes documented during the 10-year follow-up (531,097 person-years). Compared with the referents, age-adjusted relative risks (RRs) of developing type 2 diabetes for women with MHI-5 scores of 75 to 85 and 53 to 75 and depressed mood were 1.07 (95% confidence interval [CI], 0.97-1.17), 1.24 (95% CI, 1.11-1.38), and 1.42 (95% CI, 1.28-1.58), respectively (P for trend <.001). By including marital status and family history into the model, the RRs were slightly attenuated; after controlling for lifestyle factors, particularly physical activity and BMI, the RRs were “remarkably” attenuated but still significant (RR, 1.17; 95% CI, 1.05-1.30) for those with depressed mood (P for trend .002). Participants using antidepressants were at an increased risk of incident type 2 diabetes (1.25; 95% CI, 1.10-1.41) compared with the referents. Participants with only severe depressive symptoms or diagnosed depression were not at increased risk. In a parallel analysis, the researchers determined that participants with diabetes were more likely to be older than nondiabetic women. Patients with diabetes were also more likely to be without a spouse and be less likely to consume alcohol and be physically active. Compared with nondiabetic participants, those with diabetes had a higher BMI. There were 7415 incident cases of clinical depression documented during 10 years of follow-up. Compared with nondiabetic subjects, the RR of developing clinical depression in those with diabetes was 1.44 (95% CI, 1.33-1.57) in the age-adjusted model. Following adjustment for covariates, the RR was 1.29 (95% CI, 1.18-1.40). Compared with women without diabetes, for diabetic women without medications, the RR of developing clinical depression was 1.36 (95% CI, 1.19-1.55); for those with oral hypoglycemic agents, the RR was 1.42 (95% CI, 1.25-1.60); for those with insulin therapy, the RR was 1.78 (95% CI, 1.47-2.15); P for trend <.001. When major comorbidities were added to the analyses, the RRs decreased but remained statistically significant. In conclusion, the researchers said, “our results provide compelling evidence that the diabetes–depression association is bidirectional.”