Air pollution linked to childhood hypertension

Research hints at the cause
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Third-trimester exposure to airborne particulate matter (PM) smaller than 2.5 mcm in size (PM2.5) has been linked to higher levels of systolic blood pressure during childhood.

Mingyu Zhang of Johns Hopkins Bloomberg School of Public Health, Baltimore, and his associates found that the highest tertile exposure was tied to an increased likelihood of childhood elevated BP, defined as systolic blood pressure higher than the 90th percentile, compared with those in the lowest tertile (relative risk, 1.60; 95% confidence interval, 1.12-2.27).

Previous studies have shown a relationship between exposure to PM2.5and elevated BP in children and adults. Mouse models suggest that PM2.5 may interfere with in utero development of the cardiovascular system. One previous study found evidence that third-trimester exposure to PM2.5was linked to heightened BP in newborns, while a retrospective analysis showed no association with BP in adolescents.

A pregnant woman's belly Copyright fotolia
The researchers analyzed data from 1,293 mothers in the Boston Birth Cohort, who were enrolled between 1998 and 2012, as well as from children who had follow-up visits between ages 3 and 9 years.

They identified PM2.5 exposure by matching the mother’s residential address to the U.S. Environmental Protection Agency’s local air quality monitors, from which they extracted daily PM2.5 values.

For every 5 mcg/m3 increment in PM2.5 exposure, the relative risk for heightened BP in a child at a single visit was 1.46 (95% CI, 1.17-1.83). The relative risk increased after independent additions to the confounder model of birth weight (RR, 3.39; 95% CI, 0.63-6.15), gestational age (RR, 3.08; 95% CI, 0.33-5.82), and child body mass index (BMI) z score (RR, 2.75; 95% CI, 0.01-5.50).

A multivariable-adjusted cubic spline model revealed a significant increase in risk of elevated BP at a cutoff threshold of 13 mcg/m3 (RR, 1.80; 95% CI, 1.33-2.44).

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A paper recently published by the same group outlines a possible mechanism by which PM2.5 might cause harm – specifically, an increase in placental intrauterine inflammation. The study adds evidence to the case that air pollution is linked to hypertension as it includes more economically disadvantaged subjects, children of color, preterm births, and small-for-gestational-age births. Overall, the study imaginatively made use of pediatric data in a disadvantaged urban setting to better understand how air pollution affects an important physiological outcome.

Diane Gold, MD, and Antonella Zanobetti, PhD, are at the Harvard T.H. Chan School of Public Health, Boston.

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