Tiny particles such as those released from vehicle exhausts can pose a health risk, an Edinburgh study suggests.
They can work their way into the blood stream, potentially raising the risk of heart attack and stroke, researchers have found.
The findings build on previous studies that have found that air pollution is associated with an increased risk of cardiovascular disease. Researchers caution, however, that the cause remains unproven.
Experts have shown for the first time that inhaled nanoparticles can gain access to the blood stream in healthy people and those at risk of stroke.
The particles tend to build up in diseased blood vessels, where they could worsen coronary heart disease, the study found.
Lead researcher Dr Mark Miller said only a small proportion of inhaled particles can get into our blood where they can be carried to different organs of the body. However, if reactive particles like those in air pollution reach susceptible areas of the body then even a small number of particles might have serious consequences.
Researchers used gold nanoparticles for the study because it is not currently possible to measure environmental nanoparticles.
They used a range of specialised techniques to track the fate of the harmless particles after they had been breathed in by study volunteers.
The team found the gold particles migrated from the lungs into the bloodstream within 24 hours of exposure. They were still detectable in blood and urine samples three months later.
In participants at high risk of stroke, they found that gold particles had accumulated within fatty plaques that grow inside blood vessels. These plaques – which are linked to heart attack and stroke – were analysed after surgical removal as part of routine care.
We have always suspected that nanoparticles could escape from the lungs and enter the body, but until now there was no proof. These findings are of wide importance and we must now focus our attention on reducing emissions and exposure to airborne nanoparticles.
Air pollution is responsible for millions of deaths from heart attack and stroke each year. It is not known how particles that are breathed into the lungs can affect blood vessels and the heart.
The findings from this study add to a large body of evidence that inhaled particles can damage our heart and blood vessels in many different ways.
Professor Jeremy Pearson, Associate Medical Director at the British Heart Foundation, says that it is not enough for people to avoid polluted areas. He has called on the Government to put forward measures to protect the population from harm.
This study brings us a step closer to solving the mystery of how air pollution damages our cardiovascular health. More research is needed to pin down the mechanism and consolidate the evidence, but these results emphasise that we must do more to stop people dying needlessly.
The study is published in the journal ACS Nano. It was funded by the British Heart Foundation, the Colt Foundation, the Dutch Ministry of Infrastructures and Environment and the UK Department of Health.