Background:
Reports from prior studies testing whether adults with comorbid depression and diabetes have higher mortality than adults with diabetes alone are inconsistent. Explanations may include sample sizes, inadequate follow-up, or populations selected based on disease status (e.g., post- CHD). In a large sample of adults free from prevalent CHD, we tested whether the presence of depressive symptoms in persons with diabetes led to higher mortality than what would be expected by either condition alone.
Methods:
Participants from the Coronary Artery Risk Development in Young Adults Study, Cardiovascular Health Study, Framingham Offspring Study and Multi-Ethnic Study of Atherosclerosis longitudinal cohort studies who had measures available to determine diabetes, depression and mortality were included in the analysis (n=17,160). Diabetes was determined based on medication use or fasting glucose > 126 mg/dL. Centers for Epidemiologic Studies Depression (CES-D) scores > 16 (> 8 short version) indicated high depressive symptoms. We tested whether comorbid depressive symptoms and diabetes exceeded what would be expected by the sum of the two conditions independently on the additive scale by calculating the Relative Excess Risk due to Interaction (RERI; > 0 indicates interaction).
Results:
Crude mortality was highest in participants who had high depressive symptoms and diabetes, followed by participants who had diabetes and low depressive symptoms. Despite a significantly elevated adjusted hazard ratios (HR) comparing participants with diabetes who had high vs. low depressive symptoms, the RERI was 0.058 (95% confidence interval [CI]: -0.298, 0.413) indicating an absence of additive interaction. Findings were similar across strata by sex, age (< 65, >65), race (non-white vs. white) and education (< high school vs. > high school).
Conclusions:
While comorbid diabetes and depressive symptoms do not act synergistically to increase mortality, death rates are highest in this subgroup of participants.
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