Abstract
BACKGROUND: Although light-intensity physical activity (LPA) has been suggested to be associated with a lower risk of mortality, the minimal and optimal volumes of LPA remain unclear. We aimed to examine the minimal and optimal volumes of LPA associated with the risks of mortality and disease incidence (i.e., cardiovascular diseases and cancer). METHODS: Data were derived from the population-based UK Biobank cohort study, including 69,492 adults aged 43-78 years. Accelerometer-measured LPA was defined using a validated, published machine learning-based Random Forest activity method, which was categorized into 4 quartile groups. All-cause and cause-specific mortality (cardiovascular disease- and cancer-specific) were determined according to the International Classification of Diseases, 10th version codes. Disease incidence was defined based on primary care, hospitalization, or death records. RESULTS: During a median follow-up period of 8.04 years, 2024 adults died from all causes, 539 from cardiovascular disease, and 1175 from cancer. For all-cause mortality, compared with participants in the lowest quartile of LPA (<3.9 h/day), the hazard ratios (HRs) and 95% confidence intervals (95%CIs) were 0.82 (95%CI: 0.73‒0.93) for those with 3.9 to <5.0 h/day, 0.75 (95%CI: 0.66‒0.85) for those with 5.0 to <6.1 h/day, and 0.77 (95%CI: 0.68‒0.88) for those with ≥6.1 h/day, respectively. There was an inverse non-linear dose-response association between LPA and all-cause mortality, with an optimal dose of 5.72 h/day (95%CI: 5.45‒6.41; HR = 0.63, 95%CI: 0.56‒0.71) and a minimal dose of 3.59 h/day (95%CI: 3.53-8.56; HR = 0.81, 95%CI: 0.78‒0.86), with the 5th percentile as the reference. Similar patterns were observed for cause-specific mortality and disease incidence (cardiovascular disease and cancer). CONCLUSION: Engaging in LPA for ∼3.5 h/day was conservatively associated with lower risk of mortality and disease incidence, with further risk reductions observed up to an optimal dose of ∼6.0 h/day. These findings suggest that sufficient LPA offers important health benefits, which can inform the development of future PA guidelines.