- Children exposed to pollution during their mother's third trimester were 60 percent more at risk of high blood pressure
- Fine particles of pollution from cars and industrial processes get into the lungs, raising risks for respiratory trouble and illnesses
- New research from Johns Hopkins University found that pollution begins wreaking havoc even before birth
Unborn babies exposed to high levels of harmful air pollution in the womb are nearly two thirds more likely to suffer higher blood pressure in childhood, a study warned.
Those exposed to fine specks of soot spewed out in traffic fumes or from burning oil, coal and wood during the third trimester were 61 percent more likely to have elevated systolic blood pressure.
Previous research has shown fine particulate matter of 2.5 microns or less known as PM2.5 can enter the circulatory system and negatively affect human health.
The new research from Johns Hopkins University found that the damage done by the fine particles begins before birth.
Direct exposure to fine air pollution was associated with high blood pressure in both children and adults and is a major contributor to illness and premature death worldwide.
Assistant professor of epidemiology Dr Noel Mueller at the Johns Hopkins University Bloomberg School of Public Health in Baltimore said: '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
Under pressure
'High blood pressure during childhood often leads to high blood pressure in adulthood and hypertension is the leading cause of cardiovascular disease.'
The study looked at 1,293 mothers and their children who were part of the large, ongoing Boston Birth Cohort study.
Blood pressure was measured at each childhood physical examination from the ages of three to nine.
A systolic (top number) blood pressure was considered elevated if it was in the highest 10 percent for children the same age on national data.
Researchers also adjusted for other factors known to influence childhood blood pressure, such as birthweight and maternal smoking.
It found children exposed to higher levels - the top third- of ambient fine-particulate pollution in the womb during the third trimester were 61 percent more likely to have elevated systolic blood pressure in childhood compared to those exposed to the lowest level - the bottom third.
Higher exposure to air pollution in the third trimester, when fetal weight gain is the most rapid, was already known to influence lower birth weight, but the new research found the association with elevated blood pressure regardless of whether a child was of low, normal or high birth weight.
A woman's fine-particulate matter exposure before pregnancy was not associated with blood pressure in her offspring.
This provided evidence of the significant impact of in-utero exposure.
Dr Mueller added: '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 fetal growth and increase future risks for high blood pressure.'
Air pollution was measured by looking at the mother's address and readings from the nearest air quality monitoring stations to estimate exposure in each trimester of pregnancy.
In the study concentrations of PM2.5 in the highest category at 11.8 micrograms per cubic meter or higher were slightly lower than the US Environmental Protection Agency's National Air Quality Standard of 12 mg per cubic meter).
Dr Mueller said: '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 micrograms of PM2.5 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.'
The study was published in the American Heart Association's journal Hypertension.
