MINNEAPOLIS, Minnesota, December 12, 2024 (ENS) – Greater exposure to long-term air pollution has now been linked with increased risks for blood clots that occur in deep veins. A large, long-term study of Americans has found that if left untreated, these clots can block blood flow and cause serious health complications, even death.
These findings emerge from a longitudinal study funded by the U.S. National Institutes of Health that included scientists from the University of Minnesota, the University of Washington, the University of Oklahoma, and the University of Vermont.
These scientists followed 6,651 U.S. adults 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 study, titled, “Air pollution is associated with increased risk of venous thromboembolism: The Multi-Ethnic Study of Atherosclerosis,” is published in the current edition of the journal “Blood.”
“This study is the most deeply characterized analysis of pollution and VTE to date that we are aware of, and adds to mounting evidence that air pollution adversely impacts health,” the authors write.
More than one million people each year develop blood clots in their veins. This condition, known as venous thromboembolism, affects more than 20 percent of cancer patients and can be particularly deadly for them.
“VTE is the leading cause of death in cancer patients after cancer itself,” said University of Minnesota School of Public Health Professor and VTE researcher Pamela Lutsey, who led the air pollution investigation. “It’s a serious, significant problem.”
Professor, Division of Epidemiology & Community Health, University of Minnesota School of Public Health, undated (Photo courtesy U. of Minnesota)
Blood clots in deep veins, known as venous thromboembolism, VTE, include two different types of conditions. Deep vein thrombosis occurs when a blood clot forms in a deep vein of the legs, arms, or an internal organ. VTE also includes pulmonary embolism, which occurs when a blood clot breaks off from a deep vein and travels to the lungs.
These deep vein blood clots affect up to 900,000 Americans each year. Many cases occur after surgery, but other factors, including age, long periods of inactivity, heart disease, pregnancy, and genetics, can increase risks.
Exposure to air pollution, which can set the stage for inflammation and contribute to blood clotting, has long been associated with cardiovascular and respiratory diseases.
Previous research has also suggested a link to VTE, and this is the largest, most comprehensive U.S. study to report that association.
Dangerous Air Pollutants
During the course of this study, 248 adults, 3.7 percent of the study sample, developed blood clots in deep veins that required hospital care. The likelihood of this outcome was linked to anywhere from a 39 percent to a more than two-times increased risk based on long-term exposure to three different types of air pollutants.
Four indices of air pollution updated each fortnight over follow-up were averaged to estimate participant-level chronic exposure. Three of them affected the study subjects, fine particulate matter ≤2.5 micrometers in diameter (PM2.5), oxides of nitrogen (NOx), and nitrogen dioxide (NO2). The fourth, ground level ozone, had no effect.
This included exposure to PM2.5, tiny air pollution particles equal to or less than 2.5 micrometers. These particles can be inhaled during exposure to smoke from coal-burning power plants, forest fires, and motor vehicle exhaust.
PM2.5 is also created by chemical reactions between other pollutants in the air. Additionally, PM2.5 is released by tobacco smoke and home heating sources, such as wood burning stoves and fireplaces.
Participants with greater overall exposure to PM2.5 particles had a 39 percent increased associated risk for venous thromboembolism, VTE, compared to people exposed to lower levels of exposure.
People with increased exposure to oxides of nitrogen, NOx, and nitrogen dioxide, NO2, had a respective 121 percent to 174 percent increased risk. These pollutants are most often emitted from the tailpipes of fossil-fueled vehicles.
To reach these findings, the researchers analyzed the relationship between patients hospitalized for VTE and levels of air pollution collected through extensive biweekly community-level monitoring, including samples taken from participants’ homes.
The researchers then compared those samples with the highest exposure levels, the top 75 percent – to those with the lowest exposure, the bottom 25 percent. They conducted multiple analyses to control for variables associated with VTE, such as age, exposure to tobacco, and underlying respiratory and other health conditions.
Air pollution has been linked to heart disease, diabetes, cancer, and early death, and evidence has suggested negative effects on pregnancy, cognitive development in kids, and mental health, experts say.
This research study, which is part of the Multi-Ethnic Study of Atherosclerosis, was funded by contracts and grants from NIH’s National Heart, Lung, and Blood Institute and National Center for Advancing Translational Sciences, and the U.S. Environmental Protection Agency.
The American Lung Association’s 2024 “State of the Air” report reveals that spikes in deadly particle pollution are the most severe they’ve been in the history of the report. The new report finds that people in the U.S. experienced the most days with “very unhealthy” and “hazardous” air quality due to particle pollution in 25 years. In total, the report finds that 131 million people – 39 percent of Americans – are living in areas with unhealthy levels of air pollution.
More Research, More Information
Air pollution affects everyone’s health, but certain groups may be harmed more than others. Almost nine out of 10 people who live in urban areas worldwide are affected by air pollution, previous research shows.
Research funded by the National Institute of Environmental Health Sciences (NIEHS) indicates there are racial or ethnic and socioeconomic disparities in air pollution emissions. This research found that people with annual incomes above $70,000 experience greater declines in emissions from industry, energy, transportation, and commercial activities than do people with lower incomes.
Women and Children
The NIEHS-funded Children’s Health Study at the University of Southern California is one of the largest studies of the long-term effects of air pollution on children’s respiratory health. Among its findings:
- Higher air pollution levels increase short-term respiratory infections, which lead to more school absences.
- Children who play several outdoor sports and live in high ozone communities are more likely to develop asthma.
- Children living near busy roads have an increased chance of developing asthma.
- Children who were exposed to high levels of air pollutants were more likely to develop bronchitis symptoms in adulthood.
- Living in communities with higher pollution levels can cause lung damage.
Breathing PM 2.5, even at relatively low levels, may alter the size of a child’s developing brain, which may increase the risk for cognitive and emotional problems later in adolescence.
- In a large-scale study that looked at more than one million birth records, prenatal PM2.5 exposure was associated with an increased risk of cerebral palsy. While this finding adds to knowledge about environmental risk factors for cerebral palsy development and how to reduce the chance of it developing, further studies are needed.
- Prenatal exposure to PAHs was associated with brain development effects, slower processing speed, attention-deficit and hyperactivity disorder (ADHD) symptoms, and other neurobehavioral problems in urban youth.
- Prenatal exposure to air pollution may play a role in the development of ADHD-related behavior problems in childhood.
- Prenatal exposure to particulate matter was associated with low birth weight.
- Women exposed to high levels of fine particulate matter during pregnancy, particularly in the third trimester, may have up to twice the risk of having a child with autism.
- Second and third trimester exposure to PM2.5 might increase the chance of those children having high blood pressure in early life.
- A large study of more than 300,000 women found long-term exposure to air pollution, especially ozone and PM2.5, during and after pregnancy increases the risk of postpartum depression.
- The study with data on more than 5 million babies assessed associations between prenatal exposure to wildfire smoke and the risk of preterm birth. The researchers found that exposure to high levels of wildfire particulate matter during any period of pregnancy was associated with a greater chance of preterm birth.
Older adults
- NIEHS-funded researchers at the University of Washington identified a link between air pollution and dementias. This study adds evidence that ambient air fine particles increase risk of dementias. Additionally, a multi-year study published in 2022 shows improved air quality is associated with lower risk of dementia in older women. The researchers said this decline in dementia risk was equivalent to taking nearly 2 1/2 years off the ages of the women studied.
- A large, nationally representative study looked at PM2.5 from many sources and incident dementia. Emissions from agriculture, traffic, coal combustion, and wildfires, in particular, were associated with increased dementia rates.
- Air pollution was linked to a greater chance of developing neurological disorders, including Parkinson’s disease, Alzheimer’s disease, and other dementias. Hospital admissions data from 63 million older adults in the U.S., obtained over 17 years (2000-2016), was analyzed along with estimated PM2.5 concentrations by zip code. Another study with data from 10-year long exposures also found a relationship between CO and PM2.5 and an increased chance of developing Parkinson’s disease.
- Osteoporosis affects women more than men. A large study associated high levels of air pollutants with bone damage, particularly in the lumbar spine, among postmenopausal women. This study expands previous findings linking air pollution and bone damage.
- Nutrients may counter some harmful effects from air pollution. A 2020 study found omega-3 fatty acids, obtained by eating certain fish, may protect against PM2.5-associated brain shrinkage in older women.
Featured image: Polluted air hangs of the city of Minneapolis, Minnesota, Summer 2022 (Photo courtesy Minnesota Pollution Control Agency)
