In a UK Biobank cohort of 490,114 adults aged 40–69, followed from 2006 to 2022, social isolation was associated with a 34% higher hazard of all-cause mortality (HR 1.34, 95% CI 1.31–1.38) and a 49% higher hazard of cardiovascular mortality (HR 1.49, CI 1.41–1.57). Crucially, the mode of non-commute transportation modified these risks: socially isolated adults who relied exclusively on public transport faced a 17% greater cardiovascular mortality risk compared with car-only users (interaction HR 1.17), while those using a car in combination with active or public transport showed a modest but significant attenuation of all-cause mortality risk relative to car-only users (interaction HR 0.93).
This is one of the largest prospective examinations of how transportation behavior shapes social isolation's lethality. The finding that mixed transport — not car-only or public-transport-only — offers the greatest buffer is intriguing: it may reflect incidental social contact during varied travel or simply greater mobility and autonomy. The result aligns with growing evidence that built-environment factors mediate the social-connection–health pathway, complementing studies on walkability and community design. Limitations include self-reported transport mode, a single baseline measurement of isolation, and the observational design, which precludes causal inference. As a preprint not yet peer-reviewed, findings could shift materially after scrutiny. Nonetheless, the practical signal is noteworthy: encouraging transport diversity — particularly pairing car access with active or public modes — may be a modifiable lever for reducing isolation-related mortality in middle-aged adults.