Multimorbidity, Social Engagement, and Age-Related Cognitive Decline in Older Adults from the Rancho Bernardo Study of Healthy Aging.

Background: Multimorbidity is associated with increased rate of cognitive decline with age. It is unknown whether social engagement, which is associated with reduced risk of dementia, modifies associations between multimorbidity and cognitive decline.
Objective: To examine the associations of multimorbidity with longitudinal cognitive test performance among community-dwelling older adults, and to determine whether associations differed by levels of social engagement.
Methods: We used data from the Rancho Bernardo Study of Healthy Aging, a community-based prospective cohort study. Starting in 1992-1996, participants completed a battery of cognitive function tests at up to 6 study visits over 23.7 (mean = 7.2) years. Multimorbidity was defined as≥2 of 14 chronic diseases. Social engagement was assessed using items based on the Berkman-Syme Social Network Index. Multivariable linear mixed-effects models were used to test associations of multimorbidity and cognitive performance trajectories. Effect measure modification by social engagement was evaluated.
Results: Among 1,381 participants (mean age = 74.5 years; 60.8% women; 98.8% non-Hispanic White), 37.1% had multimorbidity and 35.1% had low social engagement. Multimorbidity was associated with faster declines in Mini-Mental State Examination (MMSE; β= -0.20; 95% CI -0.35, -0.04), Trail-Making Test Part B (β= 10.02; 95% CI 5.77, 14.27), and Category Fluency (β= -0.42; 95% CI -0.72, -0.13) after adjustment for socio-demographic and health-related characteristics. Multimorbidity was associated with faster declines in MMSE among those with low compared to medium and high social engagement (p-interaction < 0.01).
Conclusions: Multimorbidity was associated with faster declines in cognition among community-dwelling older adults. Higher social engagement may mitigate multimorbidity-associated cognitive decline.