By now, we all know that a world powered by fossil fuel combustion not only threatens the integrity of our ecosystems through greenhouse gas-driven climate change, but also directly jeopardizes human health by poisoning the air. Yet sometimes that abstract concept needs to be put into concrete terms to really get through to people. And a new study by the Johns Hopkins Bloomberg School of Public Health may do just that.
As reported in the journal Hypertension, 3 to 9-year-old children born to mothers who were exposed to polluted air during their third trimester were significantly more likely to have high blood pressure (BP) than those whose mothers lived in regions with cleaner air, regardless of their exposure in the intervening years.
The investigation is among the first to show that inhalation of fine particulate matter (PM), known to induce a host of severe medical conditions – including hypertension – in adults, also has lasting transgenerational effects.
"We need regulations to keep our air clean, not only for the health of our planet but also for the health of our children," study co-author Dr Noel Mueller told CBS News.
"We know that blood pressure tracks through life. Children who have elevated blood pressure in childhood have a higher probability of having hypertension later in life and cardiovascular diseases."
Mueller and his colleagues used data from 1,293 American mother-child pairs who had been followed since the child was born as part of a larger ongoing study. Exposure to fine PM was determined by averaging the daily concentration of particles recorded by the US Environmental Protection Agency air quality monitoring station nearest to the mother’s home.
Also known as PM2.5, this category of pollutants includes any liquid droplets and solid particles 2.5 micrometers in diameter (about one-thirtieth the width of a human hair) or smaller that have become aerosolized. Most PM2.5 particles are the result of chemical interactions between molecules emitted by engines, fires, and combustion-based processes at industrial plants and construction sites. Inhalation of these substances is known to cause serious short and long-term health problems and has been directly linked to millions of premature deaths each year.
According to the World Health Organization’s Air Quality Guidelines, the safe limit for PM2.5 exposure is no more than 10 µg/m3 per day averaged across the year, and no more than 25 µg/m3 during one 24-hour period.
Though the biological mechanism remains mysterious, the team believes that a PM2.5 concentration of 13 μg/m3 represents some sort of pollution threshold – children whose mothers lived in areas with concentrations at this level or above were 80 percent more likely to have elevated BP, defined as systolic pressure in the 90th percentile or higher, compared with those whose mothers lived in areas with less than 13 μg/m3 of pollution during the third trimester.
After adjusting for other factors, the researchers found that every 5-μg/m3 increment in ambient PM2.5 is associated with a 47 percent increase in risk.
Why the effect appears to be based only on third-trimester exposure, not first, second, preterm maternal, or early childhood exposure remains unknown.
The authors concede that the study shows only correlation, not causation, and it is limited by relying on only one blood pressure reading from each child. They argue, however, that the magnitude of their findings call for a whole lot more research.
