Overview
- Meeting recommended activity levels was linked to about a 30% lower risk of death overall, but this fell to roughly 12–15% where annual PM2.5 exceeded 25 μg/m³ and weakened further above 35 μg/m³, with cancer protection no longer robust at the higher level.
- The pooled study combined seven cohorts tracked for over a decade across multiple countries, including three unpublished datasets and individual‑level re‑analyses for three cohorts.
- Nearly half of the global population lives above the 25 μg/m³ threshold and about 36% lives above 35 μg/m³, placing many people in zones where exercise benefits are diminished.
- Authors emphasize that physical activity still confers health gains in polluted settings and advise practical steps such as checking air quality, choosing cleaner routes, or easing intensity on bad‑air days.
- Limitations include a dataset weighted toward high‑income countries and missing indoor‑air and diet information, with context noting UK averages near 10 μg/m³ but seasonal urban spikes that can surpass 25 μg/m³.