<p>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 7047 adults aged 50+ in the English Longitudinal Study of Ageing, we explore associations between diverse aspects of social connections and both older subjective age and accelerated physiological age using a validated physiological ageing combining cardiovascular, respiratory, haematologic and metabolic indicators. Doubly robust estimations using inverse-probability-weighted regression adjustment estimators show that living alone, low social integration and low social support are risk factors for physiological age acceleration. However, weak social connections did not have a statistically significant association with older subjective age. Analyses are robust to multiple sensitivity analyses and maintained four years later. We propose the hypothesis that accelerated physiological ageing may be a mechanism underpinning the relationship between weak social connections and age-related morbitidy and mortality.</p>