Relationships between comorbidity, physical activity and frailty: findings from the Southampton Longitudinal Study of Ageing (SaLSA)

Background Comorbidity in older adults is linked to lower physical activity and increased risk of frailty, but the role of sociodemographic factors that feed into this relationship, through association with lifestyle modifications, is underexplored. We examined this in the Southampton Longitudinal Study of Ageing. Methods 448 community-dwelling older participants completed a questionnaire which ascertained sociodemographic characteristics (relationship status, educational attainment), number of comorbidities and physical activity (Physical Activity Scale for the Elderly). Frailty components ascertained included: weight loss; self-reported exhaustion; low physical activity; low self-reported walking speed; and difficulty carrying 10 lb. Number of comorbidities in relation to physical activity and number of frailty components was examined using sex-stratified linear and Poisson regression respectively, with additional stratification by relationship status and educational attainment. Analyses were adjusted for age, BMI and smoking status. Results Among females, higher comorbidity was related to lower physical activity and a greater number of frailty components: difference in physical activity (95% CI) and multiplicative increase in number of frailty components (95% CI) per additional comorbidity was − 0.10 (-0.17,-0.03) and 1.25 (1.16,1.34) respectively. Effect sizes for physical activity and number of frailty components were similar among females when stratified according to relationship status and educational attainment. Associations were weak among males in all analyses (p > 0.27 for all associations). Conclusions Comorbidity level may have a sex-specific association with lower physical activity and increased risk of frailty, with stronger relationships observed among females, persisting across different sociodemographic groups. Females with multiple comorbidities may require targeted health interventions, regardless of their social circumstances.