Rapidly developing multimorbidity and disability in older adults: does social background matter?

Background. Multimorbidity is among the most disabling geriatric conditions. In this study, we explored whether a rapid development of multi morbidity potentiates its impact on the functional independence of older adults, and whether different sociodemographic factors play a role beyond the rate of chronic disease accumulation. Methods. A random sample of persons aged >= 60 years (n = 2387) from the Swedish National study on Aging and Care in Kungsholmen (SNAC-K) was followed over 6 years. The speed of multimorbidity development was estimated as the rate of chronic disease accumulation (linear mixed models) and further dichotomized into the upper versus the three lower rate quartiles. Binomial negative mixed models were used to analyse the association between speed of multimorbidity development and disability (impaired basic and instrumental activities of daily living), expressed as the incidence rate ratio (IRR). The effect of sociodemographic factors, including sex, education, occupation and social network, was investigated. Results. The risk of new activity impairment was higher among participants who developed multi morbidity faster (IRR 2.4, 95% Cl 1.9-3.1) compared with those who accumulated diseases more slowly overtime, even after considering the baseline number of chronic conditions. Only female sex (IRR for women vs. men 1.6, 95% Cl 1.2-2.0) and social network (IRR for poor vs. rich social network 1.7, 95% Cl 1.3-2.2) showed an effect on disability beyond the rate of chronic disease accumulation. Conclusions. Rapidly developing multimorbidity is a negative prognostic factor for disability. However, sociodemographic factors such as sex and social network may determine older adults' reserves of functional ability, helping them to live independently despite the rapid accumulation of chronic conditions.