Background: Psychological and social well-being are emerging as major determinants in preserving health in old age. We aimed to explore the association between these factors and the rate of decline in physical function over time in older adults.

Methods: Data were gathered from the Swedish National study on Aging and Care in Kungsholmen (SNAC-K). The study population consisted of 1,153 non-demented, community-dwelling men and women free from multimorbidity or impairments in basic or instrumental activities of daily living at baseline. They were followed over 12 years to capture the rate of decline in physical function, which was measured by combining data on walking speed, balance, and chair stands. The association between baseline psychological and social well-being and decline in physical function was estimated through linear mixed models, after multiple adjustments including personality and depressive symptoms.

Results: Higher levels of psychological (beta = .007; p = .037) and social (beta = .008; p = .043) well-being were significantly associated with a decreased rate of decline in physical function over the follow-up. There was a significant three-way interaction between psychological well-being*time*sex (female vs male) (beta = .015; p = .047), showing that a slower decline in physical function was observed only among women and not in men. The association was strongest for individuals with high levels of both psychological and social well-being (beta = .012; p = .019).

Conclusion: High levels of psychological and social well-being may slow down the age-related decline in physical function, which confirms the complexity of older adults' health, but also points towards new preventative strategies.