Social connections are differentially related to subjective age and physiological age acceleration amongst older adults

Human social connections are complex ecosystems formed of structural, functional and quality components. Weak social connections are associated with adverse age-related health outcomes, but we know little about the ageing-related processes underlying this. Using data from 7,047 adults aged 50+ in the English Longitudinal Study of Ageing, we explored associations between diverse aspects of social connections and both older subjective age and accelerated physiological age, which provide complementary psycho-behavioural and biological mechanistic explanations. We created and validated a novel physiological ageing index using clinical indicators pertaining to the cardiovascular, respiratory, haematologic, metabolic and cognitive systems using principal component analysis. Doubly-robust estimations using inverse-probability-weighted regression adjustment estimators showed that living alone, low social integration and high social isolation were risk factors for physiological age acceleration, with those who lived alone on average 1.4 years older than those who lived with others (95% CI 0.7-2.2 years older; 50% greater age acceleration than people who live with others). However, weak social connections were not related to older subjective age. Analyses were robust to multiple sensitivity analyses and maintained four years later. We use the findings to generate a novel hypothesis that accelerated physiological ageing may be a mechanism underpinning the relationship between weak social connections and age-related morbitidy and mortality outcomes.