Associations between multiple air pollutants and insulin resistance in Chinese adults: the moderating role of physical activity.

BACKGROUND: Exposure to air pollution may worsen insulin resistance (IR), which is a central contributor to diabetes and other metabolic disorders. However, the effects of multi-pollutant mixtures remain unclear. We investigated the associations between exposure to multiple air pollutants and two IR indices—the Chinese Visceral Adiposity Index (CVAI) and the Metabolic Syndrome Insulin Resistance (METS-IR) Index—in Chinese adults. METHODS: Using data from 4,144 adults in the CHARLS database with two observations (baseline in 2011 and follow-up in 2015), we employed generalized linear mixed models to assess individual exposure to multiple pollutants, including PM1, PM2.5, PM10, O3, NO2, CO, and SO2, and their impacts on IR. The potential moderating role of physical activity (PA) levels on these associations was also analyzed. Additionally, we explored the combined exposure effects of air pollutants on IR using weighted quantile sum (WQS) regression. RESULTS: Among participants with two observations (baseline and follow-up), the mean change in CVAI was 6 (SD = 23), and the mean change in METS-IR was 0.1 (SD = 3.7). The primary outcomes were changes in CVAI (CVAI-D) and METS-IR (METS-IR-D), defined as follow-up minus baseline values. Each interquartile range (IQR) increase in PM2.5, PM1, NO2, and SO2 was associated with increases in CVAI-D of 2.428 (95% CI: 0.238, 4.619), 1.956 (95% CI: 0.466, 3.446), 4.169 (95% CI: 1.711, 6.628), and 2.024 (95% CI: 0.185, 3.863), respectively. Similar patterns were observed for METS-IR-D. Subgroup analyses suggested that participants with regular baseline PA were more strongly affected by the adverse effects of air pollution on IR (P for interaction < 0.05). The WQS index was positively associated with both CVAI-D and METS-IR-D. For each one-unit increase in the WQS index, CVAI-D increased by 2.925 (95% CI: 1.814, 4.036) and METS-IR-D increased by 0.369 (95% CI: 0.180, 0.559), with NO2 and CO receiving the highest weights. These estimates were generally robust in sensitivity analyses. CONCLUSIONS: Long-term exposure to several air pollutants, particularly as a mixture, was associated with worsening IR indices. These associations tended to be stronger among participants reporting regular PA. The findings highlight the potential importance of reducing long-term exposure to air pollution, particularly NO2 and CO, in strategies to prevent IR and related metabolic disorders.