Dynamic changes in ambient PM 2.5 and body mass index among old adults: a nationwide cohort study.

Outdoor air pollution has been considered as a severe environmental health issue that almost affecting everyone in the world, and intensive actions were launched. However, little is known about the association between dynamic changes in ambient fine particulate matter (PM 2.5 ) exposure and body mass index (BMI) among old adults. To investigate the dynamic changes in ambient PM 2.5 and body mass index among the elderly, we included a total of 7204 participants from 28 provinces of China during 2011-2015 in the China Health and Retirement Longitudinal Study (CHARLS). Ambient fine particle matter (PM 2.5 ) was estimated using a well-validated space-time extremely randomized trees model. Change in PM 2.5 and BMI (ΔPM 2.5 and ΔBMI) were calculated as the value at a follow-up visit minus value at baseline. Linear mixed-effects models were applied to quantify the associations, controlling for sociodemographic factors. We found that per 1 μg/m 3 increase in PM 2.5 exposure was associated with a 0.031-0.044 kg/m 2 increase in BMI among the elderly. We observed an approximate linear concentration-response relationship of PM 2.5 and BMI in each visit. Each 1 μg/m 3 increase in ΔPM 2.5 exposure was associated with an increase in ΔBMI (β = 0.040, 95% CI 0.030, 0.049), while per 1 μg/m 3 decrease in the ΔPM 2.5 exposure level was associated with a decrease in ΔBMI (β = -0.016, 95% CI -0.027, -0.004). Our findings suggest that dynamic changes in ambient PM 2.5 was positively associated with changes in BMI among old Chinese population.