Long-term exposure to PM2.5 is related to increased blood pressure, with stronger connections reported in girls, according to a study of teenagers in London between the ages of 11 and 16.
The findings also show that exposure to high levels of nitrogen dioxide is associated with lower blood pressure in this group.
Researchers from the Faculty of Life Sciences & Medicine’s study team examined the potential consequences of prolonged exposure to air pollution in children attending 51 schools in the city in a report that was published on February 8th, 2023, in PLOS One.
This longitudinal study provides a unique opportunity to track exposures of adolescents living in deprived neighborhoods.
Professor Seeromanie Harding, Study Senior Author and Head, Population Health Sciences, Kings College London
She added, “Given that more than 1 million under 18s live in neighborhoods where air pollution is higher than the recommended health standards, there is an urgent need for more of these studies to gain an in-depth understanding of the threats and opportunities to young people’s development.”
When airborne pollution particles infiltrate the body through the lungs and enter the bloodstream, the blood vessels and airways become damaged. Although the impact of air pollution on blood pressure in adults is widely established, only a small amount of longitudinal research has focused on teenagers.
The period between 11-16 years of age is particularly important as adolescents continue to grow and develop. Negative effects on their organs at this stage could lead to life-long complications.
Researchers studied data from 3284 teenagers who were tracked from 11 to 13 and 14 to 16 years old. They measured systolic and diastolic blood pressure at participants schools.
According to the findings, Particulate Matter (PM2.5), a type of airborne particle that is caused by factors like construction and industrial materials and car exhaust fumes, is linked to higher blood pressure in people of all ages but is especially noticeable in girls (a μg/m3 increase in PM2.5 was linked to an increase in systolic blood pressure of 1.34 mmHg in girls and 0.57 mmHg in boys).
Adulthood hypertension, heart attacks, and strokes are all risks that are increased by high blood pressure.
It is interesting that nitrogen dioxide (NO2), a pollutant mostly caused by diesel traffic in London, was linked to decreased blood pressure. When NO2 concentration increased from a low to a high level, it nearly doubled, and the systolic blood pressure dropped by 5 mmHg for boys and 8 mmHg for girls.
Previous studies have indicated that NO2 can harm the pulmonary system, but the pollutant’s effects on the cardiovascular system are less certain.
However, a recent study from this group found that healthy adult volunteers’ blood pressure was sharply reduced by about 5 mmHg while they were seated adjacent to a lighted gas cooker, which releases NO2. A rapid rise in the blood’s circulating nitrite (NO2–) content was used to explain that impact.
The effect of NO2 on blood pressure is similar to what we and other researchers have observed previously after ingesting green leafy vegetables or beetroot juice.
Dr. Andrew Webb, Study Co-Author and Clinical Senior Lecturer, School of Cardiovascular Medicine and Sciences, Kings College London
He added, “These are rich in dietary nitrate (NO3–) which increases circulating nitrite (NO2–) concentration in the blood and lowers blood pressure, an effect which may also be sustained over weeks or months with continued ingestion of nitrate-rich vegetables. As NO2 also increases circulating nitrite (NO2–) concentration, this provides a potential explanation as to why elevated NO2 appears to be associated with lower blood pressure in the adolescents over years.”
Researchers also discovered that teenagers from ethnic minority groups experienced higher yearly average pollution concentrations at home than their white UK peers, although the effects of pollutants on blood pressure were unaffected by racial background, body mass index, or socioeconomic level.
A study in 2021 found that 3.1m children across England go to schools in areas exceeding WHO limits on PM2.5 and 98 per cent of schools in London are in areas exceeding World Health Organization pollution limits.
The findings highlight the potential detrimental role of exposure to higher concentrations of particulate matter on adolescents’ blood pressure levels. Further studies following the same adolescents over time in different socio-economic contexts are needed to understand whether and how exposure to higher pollutant concentrations may affect differently the cardiovascular health of children and adolescents.
Dr. Alexis Karamanos, Study Corresponding Author and Research Associate, Kings College London
The DASH study, a multi-ethnic longitudinal study that captures London’s diversity, provided the data. DASH is one of the few studies in the world that incorporates data on blood pressure monitoring in infancy and adolescence. Its goal is to determine what factors lead to ethnic disparities in physical and mental health throughout a person’s life.