An estimated 3.3 million deaths worldwide are caused by outdoor air pollution, according to a study published in September 2015 in the journal Nature. Of those deaths, about 75 percent are from heart attacks or strokes, while about 25 percent are from lung-related ailments, Live Science previously reported.
The majority of these deaths — about 75 percent — happen in Asia, where air pollution is particularly severe, especially in China and India. Much of this pollution results from burning fossil fuels, and global carbon emissions are on track to reach record highs worldwide in 2017, according to a report released Nov. 13, 207, by the Global Carbon Project.
The link between cardiovascular health and air pollution is well-known, but recent studies are providing a growing body of evidence that polluted air can have a range of negative impacts on physical and mental health, leading to ailments that can in some cases prove lethal.
Poor quality sperm
Elevated levels of air pollution have been linked to lower sperm quality, according to a study from Taiwan published Nov. 13 in the journal Occupational and Environmental Medicine.
Researchers investigated sperm production, activity and appearance over a series of three-month periods, in nearly 6,500 men living in Taiwan that were between the ages of 15 and 49. They then estimated how the subjects' sperm would be affected over a two-year period.
The scientists found an association between exposure to fine particulate matter in the air and abnormal sperm shape and size, they reported in the study. However, the amount of sperm produced tended to be higher when air pollution was present, perhaps to compensate for the compromised morphology of the individual sperm cells, the study authors noted.
Fractures from bone density loss
In older people, osteoporosis — age-related bone density loss — is the most common cause of bone fractures, leading to approximately 8.9 million fractures in people around the world each year, according to the International Osteoporosis Foundation. And there may be a link between air pollution and greater vulnerability to broken bones from osteoporosis, scientists reported in a study published Nov. 9, 2017, in the journal The Lancet: Planetary Health.
Researchers first evaluated data from 9.2 million people over the age of 65, investigating hospital admissions for bone fractures in the northeast and mid-Atlantic United States from January 2003 to December 2010. They compared their findings about patients with broken bones to levels of particulate matter in the air — a component of air pollution — and found that the risk of bone fractures increased when pollution levels were higher, particularly in low-income communities.
In a second stage of analysis, the researchers looked at 692 middle-age men in the Boston area, examining the impacts of their exposure to air pollution over time. They observed that men living in regions where pollution from car emissions was higher, had lower levels of parathyroid hormone, which contributes to building and maintaining bone mass. The men in highly polluted areas also had greater drops in their bone density levels than study subjects living in less polluted neighborhoods, the scientists reported.
Strokes kill an estimated 5 million people worldwide each year — they are the fifth leading cause of death in the United States and are a major cause of long-term disability, according to the Centers for Disease Control and Prevention. And incidences of stroke are on the rise, leading a team of researchers to question whether environmental factors could be to blame.
Scientists reviewed 94 studies reporting 6.2 million stroke cases in 28 countries around the world, occurring between 1948 and 2014. They were looking for associations between short-term exposure to air pollution — evaluating pollution from gasses and from particles in the air — and hospital admission or death resulting from a stroke.
They discovered a "marked and close association" between short periods of exposure to certain levels of air pollution and "adverse stroke outcomes" — disabilities and deaths — which they described in a study published in May 2015 in the journal BMJ. Though only 20 percent of the studies represented developing countries, air pollution levels tended to be highest there, and the number of strokes reported were also disproportionately high, the scientists wrote in the study.
A recent study of U.S. veterans suggested that air pollution exposure could be connected to declining kidney function, the emergence of kidney disease and even kidney failure. In the study, which was published online on Sept. 21 , 2017, in the Journal of the American Society of Nephrology, researchers reported that even low levels of air pollution could affect the kidneys, and its impact would increase linearly as pollution levels rose.
The scientists analyzed medical data representing over 2 million U.S. veterans and spanning more than eight years. They also collected information on the air pollution levels in areas where the veterans lived, which was gathered by NASA satellites. Their findings noted that air pollution levels below the recommended levels established by the Environmental Protection Agency (EPA) could be linked to kidney deterioration, with thousands of new cases of kidney disease or failure developing each year in areas where pollution levels were higher than the recommended limit, the study authors wrote.
"Even levels below the limit set by the EPA were harmful to the kidneys," Dr. Ziyad Al-Aly, director of clinical epidemiology at the Veterans' Affairs Saint Louis Health Care System, said in a statement.
"This suggests that there is no safe level of air pollution," Al-Aly added.
High blood pressure
A study of over 41,000 people living in Spain, Germany, Denmark, Sweden and Norway, found that air pollution could increase the risk of developing high blood pressure, or hypertension, as much as being overweight would. The study — published in October 2016 in the European Heart Journal — was part of an ongoing project known as "European Study of Cohorts for Air Pollution Effects" (ESCAPE), which is exploring how human health in Europe is affected by long-term exposure to air pollution.
None of the people who joined the study in 2008 suffered from hypertension when research began. But during follow-up visits with the scientists years later, 6,207 people — 15 percent of the study subjects — had developed hypertension or were taking medication to lower their blood pressure.
In the study, researchers discovered that in the cities' most polluted areas, one more person per 100 would be likely to develop high blood pressure, than in populations living in regions where the air was cleaner.
During three two-week periods between 2008 and 2011, scientists measured air pollution levels in 60 sites. They found the risk of hypertension in people that lived in the most polluted areas increased by 22 percent, compared to people living in areas where pollution was lowest.
"Our findings show that long-term exposure to particulate air pollution is associated with a higher incidence of self-reported hypertension and with intake of anti-hypertensive medication," study lead author Barbara Hoffman, a professor of environmental epidemiology at the Centre for Health and Society at Heinrich-Heine-University in Düsseldorf, Germany, said in a statement.
"As virtually everybody is exposed to air pollution for all of their lives, this leads to a high number of hypertension cases, posing a great burden on the individual and on society," Hoffman said.
Negative birth impacts
Recently, a study in mice found that exposure to air pollution during pregnancy could be connected to premature birth and low birth weight. These effects were found to be more likely to develop if exposure to polluted air occurred during the period of pregnancy in mice that was comparable to the first or second trimester in humans, according to research published on July 27 in the journal Environmental Health Perspectives.
In the study, the pregnant mice inhaled air containing invisible particles produced by burning fossil fuels, at levels that matched those in urban areas that are considered to be highly-polluted. The scientists discovered that exposure to polluted air during the earliest stage of pregnancy led to premature birth in 83 percent of the mice. If the mice were exposed to the pollutants from conception through the period marking the second trimester in a human mother, birth weight in 50 percent of the litters dropped by more than 11 percent.
"This first study of this problem in mice adds to the growing body of evidence that inhalation of particulate matter from implantation through the second trimester of pregnancy is potentially dangerous," study lead author Jason Blum, an assistant professor in the Department of Environmental Medicine at NYU School of Medicine, said in a statement.
Mental health issues
In addition to taking a toll on the body, air pollution can also fuel psychological distress, according to a study published in the November 2017 issue of the journal Health & Place.
For the study, researchers investigated air quality data from an air pollution database, alongside survey results from 6,000 participants from across the U.S. They assessed levels of psychological distress in participants using a scale that evaluated their descriptions of feelings of hopelessness, sadness, nervousness and other similar emotions.
The scientists found that as the amount of pollution in the air went up, so did the risk of the people in the study reporting instances of psychological distress. Scores representing distress were 17 percent higher in areas where air pollution was higher, and trends emerged when the study authors looked at the race of participants. In regions where the air was more toxic, the level of distress reported by black men was 34 percent higher than in white men, and the difference between black men and Latino men was even more pronounced — about 55 percent higher, the scientists reported.
And white women were especially susceptible to psychological upset in the presence of more toxic air. About 39 percent of the women in the study reported greater distress in response to rising levels of pollution, according to the study.
"This is really setting out a new trajectory around the health effects of air pollution," study co-author Anjum Hajat, an assistant professor of epidemiology in the University of Washington School of Public Health, said in a statement.
"The effects of air pollution on cardiovascular health and lung diseases like asthma are well established, but this area of brain health is a newer area of research," Hajat said.
Inhaling polluted air can cause heart inflammation and contribute to cardiovascular disease and an increased risk of death, according to the American Heart Association. In fact, air pollution causes as many heart attacks as alcohol, coffee or exercise, according to a study published in February 2011 in the journal The Lancet.
Researchers examined 36 studies describing people who had suffered non-fatal heart attacks in different countries between 1960 and 2010. They investigated various risk factors that can contribute to heart attacks, and assessed how often people came inot contact with the different factors, to determine which triggered heart attacks more frequently, Live Science previously reported.
The scientists found that air pollution accounted between 5 and 7 percent of heart attacks, while drinking alcohol or coffee accounted for about 5 percent of heart attacks apiece, and exercise covered about 6 percent.
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Mindy Weisberger is an editor at Scholastic and a former Live Science channel editor and senior writer. She has reported on general science, covering climate change, paleontology, biology, and space. Mindy studied film at Columbia University; prior to Live Science she produced, wrote and directed media for the American Museum of Natural History in New York City. Her videos about dinosaurs, astrophysics, biodiversity and evolution appear in museums and science centers worldwide, earning awards such as the CINE Golden Eagle and the Communicator Award of Excellence. Her writing has also appeared in Scientific American, The Washington Post and How It Works Magazine.