Children exposed to high levels of air pollution in late pregnancy are likely to develop high blood pressure.

Findings of a study published in the American Heart Association’s "Hypertension” journal reveals that such children are most vulnerable to the condition if air pollution affects them during the third trimester of their mother’s pregnancy.

When someone has high blood pressure or hypertension, the heart and arteries have a much heavier workload.

The heart has to pump harder and the arteries are under greater strain as they carry blood.

This puts affected children at a high risk of stroke, heart attack, kidney failure, loss of vision, and atherosclerosis (hardening of the arteries) if they do not receive effective treatment.

Children participating in the study were exposed to a type of air pollutant known as fine particulate matter weighing 2.5 micrometres or less (PM2.5). This weight is 30 times smaller than a single hair strand.

Fine particulate matter refers to air pollutants that are in the form of tiny particles or droplets. They are produced by motor vehicles or the burning of oil, coal and biomass.

They have been shown to enter the circulatory system and negatively affect human health, leading to illness and premature death worldwide.

According to the World Health Organisation (WHO), people living in cities such as Nairobi are the worst hit.

Based on previous studies, direct exposure to this type of pollution has been linked to high blood pressure in both children and adults.

However, this new study showed that children can suffer the effects of pollution through indirect exposure to the fine particles during pregnancy.

"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,” said Noel Mueller, senior author of the study and assistant professor of epidemiology at the Johns Hopkins University, Bloomberg School of Public Health in Baltimore, Maryland.

"High blood pressure during childhood often leads to high blood pressure in adulthood and hypertension is the leading cause of cardiovascular disease.” The researchers examined 1,293 mothers and their children in Boston, Massachusetts.

Childrens’ blood pressure was measured at three to nine years old. The results showed that children exposed to high levels of the fine particulate pollution during the third trimester were 61 per cent more likely to have elevated blood pressure compared to those exposed to lower levels.

However, the research found that a woman’s exposure to pollution before pregnancy was not associated with blood pressure in her offspring. This showed that the exposure is very critical during pregnancy.

"These results reinforce the importance of reducing emissions of PM2.5 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 foetal growth and increase future risks for high blood pressure,” Dr Mueller said.

"We need regulations to keep our air clean, not only for the health of our planet but also for the health of our children.”

Pregnant women can reduce their vulnerability to this type of pollution by not smoking as well as staying away from people doing so. This will cushion them from inhaling second-hand smoke. They are also advised to limit their use of fireplaces, wood stoves or charcoal jikos.

It is also important for motorists to switch to clean fuels such as low sulphur diesel that minimise air pollution. According to WHO, outdoor air pollution is a major cause of death and disease globally.

The health effects range from increased hospital admissions and emergency room visits to increased risk of premature death.

Agencies