Long-term exposure to fine particulate matter ≤2.5 μm in diameter (PM_2.5), which is below current regulatory thresholds in the U.S., may contribute to increased hypertension risk, according to a national cohort study published April 15 in JACC. These findings emphasize the need to reconsider existing air quality standards to protect public health.

Yechi Zhang, MPH, et al., used the Medicare database to develop a cohort of adults aged ≥65 years in the U.S. residing in ZIP codes where annual PM_2.5 concentrations concisely remained below the U.S. Environmental Protection Agency annual standard of 9 μg/m³ throughout the study period of Jan. 1, 2017 to Dec. 31, 2022. Daily concentrations of ambient PM_2.5 at 1 km × 1 km spatial resolution across the contiguous U.S. were obtained from the USHighAirPollutants dataset. A total of 26,774,588 beneficiaries residing in 19,488 ZIP codes were included in the analysis.

Study results showed a 2.8% increase in hypertension-related hospitalization among all beneficiaries, which was associated with each 1-μg/m³ increase in the annual PM_2.5 concentration and comparable with estimates from conventional quasi-Poisson regression models.

Notably, greater vulnerability was observed among women, individuals in more socioeconomically deprived neighborhoods, individuals living in rural or suburban areas, and residents of the Midwest and Northeast regions of the U.S. A stronger association was also found among White and Other racial groups.

Despite study limitations including the possibility of exposure misclassification, lack of individual-level factors and limited detailed clinical information, the authors believe their findings "contribute to the growing body of evidence suggesting that adverse health effects may occur even below the existing regulatory standards." They emphasize the need for future studies "to disentangle and better characterize the distinct and overlapping biological pathways underlying short-term and long-term effects of PM_2.5 exposure..."