Dose-response interplay between light and moderate-to-vigorous physical activity on all-cause mortality risk: a causal inference analysis

OBJECTIVE: We employed a causal inference framework to estimate the counterfactual dose-response effects of light-intensity physical activity (LPA) on mortality across low, medium and high moderate- to vigorous-intensity physical activity (MVPA) levels, and the lower and higher thresholds of current MVPA recommendations. METHODS: Eligible participants from the UK Biobank (n=71 715) were included in the current study. LPA and MVPA were measured via accelerometers, and mortality data were derived from death registry. Flexible parametric survival models were used under the counterfactual framework to estimate the marginal predicted probability of death after 10 years of follow-up. RESULTS: During a median follow-up period of 8.0 years, 2195 deaths occurred. A non-linear dose-response effect of LPA on all-cause mortality was evident, and the effect diminished as MVPA level increased. If all participants achieved the lower threshold of the WHO recommended 22 min/day of MVPA, the 10-year probability of death would be expected to decrease from 9.5% at 60 min/day LPA to 4.2% at 360 min/day. If all participants achieved the higher threshold of 44 min/day of MVPA, the 10-year probability of death would be expected to decrease from 6.6% at 60 min/day of LPA to 3.7% at 345 min/day. Across the MVPA values examined, the optimal dose for LPA ranged from 195 to 225 min/day. CONCLUSION: LPA may complement MVPA to reduce risk of all-cause mortality, particularly among those with low MVPA or those unable to engage in higher-intensity activities. Our study highlights the potential for integrating LPA into public health strategies and future physical activity guidelines.