Breakthrough study shows higher BP more likely in children exposed to higher levels of pollution in utero

Elevated blood pressure (BP) may be more likely in children between the ages of 3 and 9 years who were exposed to higher levels of air pollution in the third trimester of their mother’s pregnancy, according to results from one of the first studies to show the negative health effects of exposure to air pollution during pregnancy. The results were published in the journal Hypertension.

“Ours is one of the first studies to show breathing polluted air during pregnancy may have a direct negative influence on the cardiovascular health of the offspring during childhood,” said senior author Noel T. Mueller, PhD, MPH, assistant professor of epidemiology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD. “High BP during childhood often leads to high BP in adulthood, and hypertension is the leading cause of cardiovascular disease.”

Previous studies have shown that direct exposure to fine-particulate air pollution, which is comprised of fine particulate matter of 2.5 µm (PM_2.5) or less and produced by motor vehicles and burning oil, coal, and biomass, is associated with increased BP in both children and adults. The fine particulate matter enters the circulatory system and is a major contributor to illness and premature death throughout the world.

Dr. Mueller and his fellow researchers included 1,293 women and their children from the Boston Birth Cohort study. They estimated exposure to air pollution in each trimester of pregnancy using the residential addresses of each woman and data from the nearest US Environmental Protection Agency’s (EPA) air quality monitor.

At each childhood physical exam, BP was measured. Researchers defined elevated systolic BP as in the highest 10% for children of the same age according to national data. Results were adjusted for other risk factors known to affect childhood BP, including birthweight and maternal smoking.

Dr. Mueller and colleagues observed that children in the top third level of exposure to ambient fine-particulate pollution in the womb during the third trimester were 61% more likely to have elevated systolic BP in childhood, compared with those in the bottom third level of exposure. The result did not change when birthweight was factored into the analysis.

The significant impact of in utero exposure was highlighted by their finding that a woman’s exposure to fine particulate matter before pregnancy had no association with elevated BP in her children.

“These results reinforce the importance of reducing emissions of PM_2.5 in the environment. Not only does exposure increase the risk of illness and death in those directly exposed, but it may also cross the placental barrier in pregnancy and effect fetal growth and increase future risks for high blood pressure,” said Dr. Mueller.

Also important to note is their finding that PM_2.5 concentrations in the highest category of exposure in their study ( ≥ 11.8 µg/m³) were associated with high BP in childhood. This measurement is below the 12 µg/m³ standard set by the EPA’s National Air Quality Standard and highlights the need to maintain or even decrease this benchmark.

“The science on the health effects of air pollution is under review by the EPA. The findings of our study provide additional support for maintaining, if not lowering, the standard of 12 µg of PM_2.5 per cubic meter set in 2012 by the National Ambient Air Quality Standards under the Clean Air Act. We need regulations to keep our air clean, not only for the health of our planet but also for the health of our children,” concluded Dr. Mueller.

The Boston Birth Cohort received grant support from The March of Dimes Birth Defects Foundation, the National Institute of Child Health and Human Development, and the Maternal and Child Bureau of the Health Resources and Services Administration.