We know air pollution is harmful to the environment and our bodies, but we are still learning the depth of the problem. There's the risk of respiratory diseases, fatigue and headaches, anxiety, cardiovascular damage, harm to reproductive organs, damage to the liver, spleen, blood and even the nervous system, according to Active Sustainability.
Long-term exposure to air pollution can lead to emphysema, a chronic lung condition most often linked to smoking, a study published in the Journal of the American Medical Association found. Exposure to air pollution — especially ground-level ozone — is like smoking a pack of cigarettes every day for decades.
"The increase in emphysema we observed was relatively large, similar to the lung damage caused by 29 pack-years of smoking and 3 years of aging," said senior author R. Graham Barr, M.D., professor of medicine and epidemiology at Columbia University Irving Medical Center, in a statement. (One pack-year means smoking a pack of cigarettes a day for a year.)
And while lung damage may seem obvious, there are more insidious connections.
"Environmental risks like air pollution are not large in magnitude — their importance comes because everyone in the population is exposed," Scott Weichenthal from Canada's McGill University, told The Guardian. Weichenthal was the lead author on a study that linked air pollution nanoparticles to brain cancer for the first time. "So when you multiply these small risks by lots of people, all of sudden there can be lots of cases. In a large city, it could be a meaningful number, particularly given the fact that these tumors are often fatal."
There are also a number of other ways pollution harms our health that aren't as well known. Here are just a few:
1. Pollution and intelligence
When we think of the toll air pollution takes on our health, we usually think about it in terms of its physical impact. But, studies have shown that this goes beyond physical health; our cognitive skills can be affected as well.
A study conducted in China and published in PNAS, the Proceedings of the National Academy of Sciences, found that breathing unsafe air for too long can create an effect that's equal to losing a year's worth of intelligence, reports The Guardian. According to the collected research, those who are consistently exposed to polluted air can experience a large drop in language and arithmetic scores.
"Polluted air can cause everyone to reduce their level of education by one year, which is huge," said team research member Xi Chen at Yale School of Public Health. "But we know the effect is worse for the elderly, especially those over 64, and for men, and for those with low education. If we calculate [the loss] for those, it may be a few years of education."
The researchers examined language and arithmetic tests administered as part of the China Family Panel Studies to 20,000 people throughout China between the years of 2010 to 2014. The results were studied in correlation to the amount of nitrogen oxide and sulphur dioxide pollution levels in the air at the time.
The longer individuals were exposed to the harmful air, the larger the loss of cognitive functioning. Language abilities took a bigger hit than arithmetic abilities.
2. Pollution and dementia
Researchers in the United Kingdom discovered that air pollution can potentially raise dementia risks by 40%, according to a study published in BMJ Open.
The research team examined a population of 131,000 Londoners aged 50 to 70 who were registered patients of local doctors' practices.
The team looked at the postal codes of participants to get a rough estimate of their exposure to nitrogen dioxide, ozone pollution, traffic and road noise pollution, as well as heavy amounts of particulate matter (all the fine particles in the air that are toxic).
Participants exposed to the highest levels of nitrogen dioxide had a 40% higher risk of developing dementia than those with lower exposure.
"As air pollution has been linked with vascular problems in other studies including heart disease and stroke and thus, if anything, we expected to see a link with vascular dementia," Dr. Iain Carey, lead study author of St. George's, University of London, told Newsweek.
"However when we looked at specific diagnoses, we only saw a link with Alzheimer's disease, not vascular dementia in this study," said Carey.
So, while the link isn't definite, it's certainly a possibility.
The team looked at 7 million adults aged 20 to 85 living in Ontario by using their postal codes. Researchers considered people who lived near highways and roads with heavy traffic, and compared the data with the number of individuals who developed some sort of neurodegenerative condition — like Alzheimer's and Parkinson's diseases.
They found that those living within 50 meters (165 feet) of a major highway or roadway had a 4% increased risk of developing dementia. The further a person lived from major highways and roadways, the risk decreased. Once someone's home was beyond 200 meters (650 feet) from major roads, there appeared to be no risk.
A study published in the journal Translational Psychiatry suggests that women living in areas with unsafe levels of particulate matters are possibly at twice the risk of developing dementia.
3. Air pollution and mental disorders
A study conducted by Hong King Polytechnic University revealed that those with mental and behavioral disorders have a higher chance of dying on days when air pollution reaches extreme heights, The Guardian reports. The research was published in Environmental International.
Researchers looked at a decade's worth of death records and statistics, and found that death risks increase 16% on the first day of heavy haze, and rise to 27% on the second day. In the event that heavy ozone pollution is added to the mix, the mortality risk rises to 79%.
This most recent research somewhat ties into earlier research that examined increased air pollution and instances of suicide.
"Although we do not yet understand how pollutants inhaled into the lung affect cognitive function, these new findings from Asia are compatible with a recent Belgian study that reported an association between short-term increases in air pollution and suicide," Johnathan Grigg of Queen Mary University told The Guardian. Grigg didn't participate in the study.
For the study, researchers examined the link between death risk and haze days. Haze days are when the level of pollutants in the air are high enough that the sky's visibility is obscured.
"Although a hazy day generally has 2.9% higher risk [of death] than a day without haze, a very intense adverse effect is found on the mortality associated with mental and behavior disorders," says the research team. "A combined influence of haze, extreme weather/air quality and urban environment can result in extremely high mortality."
Research team member Lin Yang of Hong Kong Polytechnic University told The Guardian. "Haze days are very likely to trigger an acute depression response in people. This has been shown in surveys in Indonesia, where there was a big disaster of haze from forest fires."
Further research proves how pervasive the problem is. In a meta-analysis published in Environmental Health Perspectives, scientists reviewed research compiled from January 1974 to September 2017. The data revealed a strong statistical link between toxic air and depression and suicide. This was true across the globe.
While the scientists say they don't know that air pollution is causing depression, but they believe there is a connection.
"We've shown that air pollution could be causing substantial harm to our mental health, making the case for cleaning up the air we breathe even more urgent," Isobel Braithwaite, at University College London (UCL), who led the research, told The Guardian.
4. Pollution and mental illness in children and adolescents
Researchers in Sweden conducted a study that found a connection between air pollution and increased risk for mental illness in children, The Guardian reports. The study was published in the journal BMJ Open.
Researchers looked at the medical records of 500,000 Swedes under the age of 18 and found that more children and adolescents living in areas where air pollution was higher were prescribed drugs such as anti-psychotics and sedatives for various psychiatric disorders.
"The results can mean that a lower concentration of air pollution, first and foremost from traffic, may reduce psychiatric disorders in children and adolescents," study leader Anna Oudinof of Umea University said. "I would be worried myself if I lived in an area with high air pollution."
Professor Frank Kelly of King's College in London, who was not part of the study, noted that the research "builds on existing evidence that children are particularly sensitive to poor air quality probably because their lifestyles increase the dose of air pollution they are exposed too — i.e. they are more active — and that developing organs may be more vulnerable until they fully mature."
Interestingly, Sweden isn't known for high air pollution.
"This suggests that other countries and cities have an even bigger challenge, as they will have to make significant improvements to their air quality so that it is even cleaner than Sweden's," says Kelly.
5. Pollution and miscarriages
A study published in the journal Fertility and Sterility suggests that air pollution can increase the risk of miscarriage in the early stages of pregnancy by more than 10%. Researchers at the U.S. National Institute of Child Health and Development looked at records from a long-term study conducted by the National Institutes of Health which studied 501 couples between 2005 and 2009.
"We found that both ozone and particles in the air were related to an increased risk of early pregnancy loss," senior researcher Pauline Mendola told WebMD.
Of the 501 couples, women from 343 of the couples became pregnant; 98 of the 343 women (28%) had a miscarriage within 18 weeks of the pregnancy.
The researchers examined pollution levels in the areas where the couples lived to see if the pollution may have had some connection to the miscarriages.
They found that exposure to air pollution in the ozone increased miscarriage risk by 12%, and that exposure to airborne particles raised the risk to 13%.
It's not clear that air pollution was the direct cause of the miscarriages, but the researchers think there may be an association.
Mendola hypothesized that oxidative stress and inflammation due to air pollution can impede the development of both the fetus or placenta, or even cause problems with implantation of fertilized eggs.
Dr. Jill Rabin, co-chief of ambulatory care with Women's Health Programs-PCAP Services at Northwell Health in New Hyde Park, New York, suggests toxins may be able to directly penetrate the placenta and cause harm to the fetus.
"It's incomprehensible that something you're breathing in that's toxic wouldn't affect young developing tissue," Rabin told WebMD. "It's conceivable some of those toxins would be able to get through the placenta and to the baby."
6. Pollution and premature birth
A study published in Environmental International conducted by researchers at The Stockholm Environmental Institute at the University of York, saw that in 2010, roughly 2.7 million premature births worldwide (18%) were potentially linked to a harmful, atmospheric fine particulate matter known as PM2.5.
PM2.5 is fine particulate matter that mainly comes from agricultural waste-burning, forest fires, power plants, diesel vehicles and airplanes. PM2.5 is harmful to the lungs in particular.
"This study highlights that air pollution may not just harm people who are breathing the air directly — it may also seriously affect a baby in its mother's womb," Chris Malley, a researcher in SEI's York Centre at the University of York and lead author of the study, said in a release.
In 2010 about 14.9 million babies were born prematurely overall. Roughly 14 to 15% of these preterm births occurred in African and South Asian countries — regions where there are large concentrations of PM2.5.
The number of preterm births in South Asia and East Asia were exorbitant. About 1 million of the 2.7 million premature births believed to have a connection with high amounts of PM2.5 occurred in India, and 500,000 occurred in China.
7. Pollution and autism in children
A study conducted by The Harvard School of Public Health, suggests a connection between air pollution and autism risks for children. The study was published in Environmental Health Perspectives.
A child could be twice as likely to develop autism if he is born to a mother exposed to high levels of particulate matter during her pregnancy — especially during the third trimester of the pregnancy.
"Our data add additional important support to the hypothesis that maternal exposure to air pollution contributes to the risk of autism spectrum disorders," Marc Weisskopf, senior author of the study, said in a statement. "The specificity of our findings for the pregnancy period, and third trimester in particular, rules out many other possible explanations for these findings."
The children were all offspring of participants in the Nurses' Health Study II (Now the Nurses' Health Study III.) The Nurses' Health Study is among the largest prospective investigations into the risk factors for major chronic diseases in women.
The research team looked at data of the participants based on their place of residences and the U.S. Environmental Protection Agency (EPA).
Children who lived in areas where there is a higher concentration of PM2.5 were more likely to be diagnosed with autism. The connection between autism and PM2.5 exposure was considered before, during (including each trimester), and after pregnancy.
"The evidence base for a role for maternal exposure to air pollution increasing the risk of autism spectrum disorders is becoming quite strong," Weisskopf said. "This not only gives us important insight as we continue to pursue the origins of autism spectrum disorders, but as a modifiable exposure, opens the door to thinking about possible preventative measures."
8. Pollution and the development of babies' brains
In 2017, UNICEF published a report that found 17 million babies under the age of 1 living in South Asia are breathing in toxic air, which can cause a hindrance to their brain development, reports India Today.
The ways in which air pollution affects the brains of babies are mostly neurogenerative issues.
Particulate matter that is equal to or less than 2.5 micron (a micron is one millionth of a meter), can enter our bloodstreams with relative ease and make its way to the brain with little effort, harming the blood-brain barrier and causing damage. The blood-brain barrier is a brain membrane that helps to shield the brain from toxic substances.
Damage to the blood-brain barrier can cause neuroinflammation which can cause neurodegeneration conditions. While children aren't in danger of Alzheimer's at such a young age, exposure to anything causing neurodegeneration at a developmental stage can be seen as detrimental.
In addition, air pollution particles such as magnetite — the most magnetic of all naturally occurring minerals — are of such minuscule size that they are able to make their way into the body via the gut and olfactory nerve. Magnetite's toxicity is due to its magnetic charge which creates oxidative stress. Oxidative stress is also capable of causing neurodegenerative conditions.
Polycyclic Aromatic Hydrocarbons — pollutants formed from fossil fuels — have shown to cause harm to white matter in the brain. White matter is responsible for neural communication within the brain. Without white matter that functions properly, communication between neurons becomes difficult.
All three of these factors can cause significant challenges to the development of a healthy and functional brain.
9. Pollution and DNA changes
Heavy air pollution seemed to change DNA patterns. (Photo: Caroline Davis2010 [CC BY 2.0]/Flickr)
It's also been suggested that exposure to air pollution can causes changes in our DNA.
In another study, researchers at the University of British Columbia asked volunteers to sit in a walled-in aquarium where pollution levels of the world's most polluted cities were simulated, filling the room with diesel exhaust. The participants sat in the room for two hours.
The researchers took a blood sample from the participants before entering the room, and after exiting the room. While the participants' DNA wasn't completely changed after sitting in the smog-filled space, the researchers did notice that there was a difference in their DNA methylation patterns upon exiting the room. DNA methylation patterns are the layer of methyl molecules that turn genes on or off.
The results were the same across the board for all participants — meaning the connection between DNA alteration and heavy pollution is a strong possibility.
Does all this mean we need to pack up and move to areas where pollution is less present? Probably not — and that doesn't seem like it would fix much anyway. What all this information does signify, though, is that it's clear air pollution is a problem in many more ways than we may have previously thought.
In case you're curious as how to pollution levels are rising, taking a look at this interactive map, courtesy of The Revelator, which shows where pollution levels are headed country by country, and gives us a look at the state of things by the year 2100.
10. Pollution and bone health
Air pollution may make our bones weaker. After measuring levels of PM2.5 in Hyderabad, South India, researchers analyzed the health of 3,717 people who lived in 28 surrounding villages. They looked to see whether they had changes in bone mineral content, which is used to measure bone strength and diagnose osteoporosis.
“What we see overall is a quite consistent pattern of lower bone mineral content with increasing levels of air pollution,” co-author Cathryn Tonne at the Barcelona Institute for Global Health, told New Scientist.
The people in the study were exposed to average annual PM2.5 levels of 32.8 micrograms per cubic meters — that's three times higher than what is considered safe by the World Health Organizations. Researchers found that every additional 3 micrograms per cubic meters of PM2.5 was associated with relatively minimal, but still notable drops in bone mineral density in the spine and hip.
The research was published in the journal JAMA Network Open.
Editor's note: This story has been updated with new information since it was published in May 2019.