By Tarun Sai Lomte Reviewed by Lauren Hardaker Dec 3 2025 A large multi-country study identifies the air pollution levels at which the health benefits of regular physical activity start to decline, offering clearer guidance for staying active in areas with rising PM2.5 exposure. Study: Does ambient PM2.5 reduce the protective association of leisure-time physical activity with mortality? A systematic review, meta-analysis, and individual-level pooled analysis of cohort studies involving 1.5