Long-term exposure to air pollution linked to blood clots in veins that supply blood to the heart

A large study has found that greater exposure to long-term air pollution is linked to an increased risk of blood clots that can occur in deep veins and, if left untreated, can block blood flow and cause serious complications and even death.

These findings came from a longitudinal study that included 6,651 American adults who were followed for an average of 17 years between 2000 and 2018. Participants lived in or near one of six major metropolitan areas: New York, Baltimore, Chicago, Los Angeles, Minneapolis, and Winston-Salem, North Carolina. The findings are published in Blood.

During the study, 248 adults, 3.7% of the study population, developed blood clots in deep veins that required hospital care. The likelihood of this outcome was associated with a risk of 39% to a more than twofold increased risk based on long-term exposure to three different types of air pollutants.

Blood clots in deep veins, collectively known as venous thromboembolism (VTE), include deep vein thrombosis, which occurs when a blood clot forms in a deep vein of the legs, arms, or an internal organ, and pulmonary embolism, which occurs when a blood clot arises. blood clot breaks off from a deep vein and travels to the lungs.

Exposure to air pollution, which can trigger inflammation and contribute to blood clotting, has long been linked to cardiovascular and respiratory diseases. Although previous research has also suggested a link with VTE, this is the largest and most comprehensive US study reporting the link with three different types of air pollutants.

This included exposure to small air pollution particles equal to or smaller than 2.5 micrometers, which can be inhaled from a variety of sources, including smoke from coal-fired power stations, forest fires and motor vehicle exhaust. Participants with greater overall exposure to these types of air pollution had a 39% increased risk of VTE compared to people exposed to lower levels.

People with increased exposure to nitrogen oxides and nitrogen dioxide, pollutants most commonly found in vehicle exhaust, had an increased risk of 121% to 174%, respectively.

To arrive at these findings, the researchers analyzed the relationship between patients hospitalized for VTE and air pollution levels collected through extensive biweekly monitoring at the community level, including samples taken from participants’ homes. They then compared those with the highest exposure levels – the top 75% – with those with the lowest exposure – the bottom 25%.

They also conducted multiple analyzes to control for variables associated with VTE, such as age, tobacco exposure, and underlying respiratory and other health problems.

VTE affects up to 900,000 Americans each year. Many cases occur after surgery, but other factors, such as age, long periods of inactivity, heart disease, pregnancy and genetics, can increase the risks.

The research is part of the Multi-Ethnic Study of Atherosclerosis (MESA).