Additive and interactive effects of comorbid physical and mental conditions on functional health

Objective: To understand the role of cognitive impairment and depressive symptoms on functional outcomes of stroke and diabetes. Evaluation approaches to functional outcomes have rarely focused on the presence of specific comorbidities, particularly those involving mental health disorders. Methods: Data are from the AHEAD cohort of the Health and Retirement Study (HRS), a nationally representative panel of persons 70+ years of age in 1993. Analyses are limited to 5,646 self-respondents for whom functional outcome data are available in 1995. Additive and interactive multiple regression models are compared for each outcome and focal condition combination. Results: The additive model is sufficient for the majority of outcome and focal condition combinations. The interaction term is significant in 4 of 12 comparisons. Discussion: Stroke, diabetes, cognitive impairment, and depressive symptoms exhibit strong independent effects on physical functioning. Support for the hypothesis that cognitive impairment and depression exacerbate the impact of stroke and diabetes is more limited.