Temperature variability, extreme temperature events, and arthritis risk in older adults: interaction with PM2.5 chemical components.

Ambient temperature and fine particulate matter (PM2.5) are important environmental determinants of chronic disease, yet their joint effects remain insufficiently understood. This study investigated the joint effects of long-term temperature-related exposures (annual mean temperature, diurnal temperature range [DTR], heatwaves, and cold spells) and PM2.5 chemical components on arthritis risk among 11,057 older adults in China. Cox proportional hazards models with time-varying exposures were applied to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). We assessed multiplicative interactions between temperature-related exposures and PM2.5 components. Over the follow-up period, 3,042 (27.5%) participants developed arthritis. A 1°C increase in annual temperature was associated with a 4.3% lower risk of arthritis (HR 0.957, 95% CI 0.946 to 0.968), while a 1°C increase in DTR was associated with an 8.5% higher risk (HR 1.085, 95% CI 1.050 to 1.121). Cold spells were likewise associated with elevated arthritis risk. Notably, higher PM2.5 component levels attenuated the temperature-related risks (P for interaction <0.05 for most components). These findings suggest that colder temperature patterns and greater diurnal variability are important environmental risk factors for arthritis, and that temperature and air pollution should be considered jointly in relation to arthritis risk.