Air pollution in London is linked to higher blood pressure in teenagers, particularly for girls, according to a new study by King’s College London.

Long-term exposure to a pollutant known as PM2.5 is associated with higher blood pressure in secondary school children aged 11-16. The findings show how exposure to high levels of air pollution in childhood can raise the risk of hypertension, heart attacks and strokes in adulthood.

The study also found that exposure to high levels of nitrogen dioxide (NO2) is associated with lower blood pressure.

The study, one of only a few to look at the effects of air pollution in adolescents, is published in PLOS One. The researchers say there is an urgent need to understand how pollution affects the cardiovascular health of children over the long term.

Air pollution particles are inhaled into the body and can get into the bloodstream, causing damage to blood vessels and airways. PM2.5 are tiny pollutants which come from car exhaust fumes, as well as building and industrial materials.

Previous research has shown NO2 may have damaging effects on the respiratory system, but the impacts of the pollutant on the cardiovascular system are less clear. For children, the period between 11-16 is critical as their bodies are growing and developing, and adverse effects on their organs at this stage can lead to life-long complications.

The researchers looked at the long-term exposure in children attending 51 schools across the capital, with 80% of the cohort from ethnic minority groups who are exposed to higher annual average concentrations of pollutants at residential postcodes than their White peers. Data from 3284 adolescents was analysed with researchers measuring the children's systolic and diastolic blood pressure at ages 11-13 and following up at 14-16 years old.

The results show high levels of PM2.5 in the air were associated with higher blood pressure across all ages. A 1 μg/m3 increase in PM2.5 was associated with a 1.34 mmHg increase in systolic BP for girls and a 0.57 mmHg increase in systolic blood pressure for boys.

Even though minority ethnic groups were exposed to more pollution at home, the impact of pollution on blood pressure was the same across all ethnicities.

Professor Seeromanie Harding from King’s College London said: ‘Given that more than one million under 18s live in neighbourhoods 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.’

NO2, a pollutant from diesel traffic, was associated with lower blood pressure across all ages and ethnicities.

Dr Andrew Webb, a co-author of the study from King's College London, said that the effect of NO2 on blood pressure is similar to research on the impact of ingesting green leafy vegetables or beetroot juice.

He explained: ‘These are rich in dietary nitrate, which increases circulating nitrite concentration in the blood and lowers blood pressure. As NO2 also increases circulating nitrite concentration, this provides a potential explanation as to why elevated NO2 appears to be associated with lower blood pressure in adolescents over years.’