Prospective Disability in Different Combinations of Somatic and Mental Multimorbidity.

Background: Multimorbidity (multiple co-occurring chronic conditions) may be an important contributor to disability and poor health-related quality of life. The functional consequences of specific combinations of somatic and mental health conditions are unclear. Methods: Nationally representative prospective cohort study using the National Health and Aging Trends Study data of Medicare beneficiaries. We included 4,017 participants aged 65 years or older interviewed in 2013 and 2014. The primary outcome was prospective activities of daily living (ADL)-instrumental ADL (IADL) index (range = 0-11) assessed in 2014. All other measures were assessed in 2013. Chronic conditions included heart disease, hypertension, stroke, diabetes, arthritis, lung disease, osteoporosis, cancer, depression, and cognitive impairment. Analyses were adjusted for age, sex, education, race/ethnicity, body mass index, and baseline ADL-IADL. Results: Thirty-four percent of multimorbidity combinations included depression, cognitive impairment, or both. Relative to multimorbidity combinations of exclusively somatic conditions, combinations that included both depression and cognitive impairment were associated with 1.34 times greater ADL-IADL in adjusted models (95% confidence interval [CI]: 1.09, 1.64). Relative to combinations of both depression and cognitive impairment, combinations of cognitive impairment and somatic conditions were associated with 0.84 times lower ADL-IADL in adjusted models (95% CI: 0.74, 0.96); combinations of depression and somatic conditions were associated with 0.72 times lower ADL-IADL in adjusted models (95% CI: 0.62, 0.85). Conclusions: Depression and/or cognitive impairment was identified in one-third of older adults with multimorbidity, and these combinations were associated with substantially greater prospective disability than combinations comprised exclusively of somatic conditions. This argues for identifying and managing mental health conditions that co-occur with somatic conditions.