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Childhood Asthma and Traffic-Related Air Pollution

By Roberta Attanasio

“I explain it to people like you are breathing through a coffee stirrer straw, and you just can’t get enough breath. The attacks can happen so quickly and out of nowhere, so I feel like I’m really not in control of my own body. Not being able to breathe in and out the way my body is designed to do is quite scary” says one of the 19 million adults who currently have asthma in the US.

Asthma is a chronic disorder that causes swelling and inflammation in the lungs—the airways narrow and produce extra mucus, making breathing difficult and causing coughing, shortness of breath and wheezing, a high-pitched whistling sound made while breathing. Asthma attacks, in absence of appropriate treatment, can be life-threatening. Exposure to various irritants and substances that trigger allergies—as for example pollen, dust mites, mold spores, pet dander, smoke and certain medications—can also trigger signs and symptoms of asthma. However, asthma triggers are different from person to person.

According to the National Center for Health Statistics, asthma also affects 6.2 million children in the US. Indeed, childhood asthma is the most common serious chronic disease in infants and children. Alarmingly, asthma is now the most commonly reported non-communicable disease among children worldwide.

Children are especially vulnerable to air pollution, one of the major triggers of asthma attacks. Research indicates that air pollutants suppress genes that regulate the immune system’s ability to differentiate harmless substances from dangerous viruses or bacteria. The immune system then sets up an inflammatory response which leads to asthma.

Notably, results from a recent study show that millions of children worldwide develop asthma annually due to a specific type of pollution—traffic-related air pollution. The study, based on data from 2010 to 2015, focuses on a particular type of traffic-related pollutant—nitrogen dioxide, or NO2—and estimates that 64 percent of these new cases of asthma occur in urban areas. NO2 is one of a group of gases called nitrogen oxides. While all of these gases are harmful to human health and the environment, NO2 is of greater concern. It forms from emissions from cars, trucks and buses, power plants, and off-road equipment, and irritates airways in the human respiratory system. For the study, researchers used a method that takes into account high NO2 exposures occurring near busy roads. They were then able to estimate the number of new pediatric asthma cases attributable to NO2 pollution in 194 countries and 125 major cities worldwide.

Of the 125 major cities, the highest traffic-related air pollution effects on asthma were found in Lima, Peru; Shanghai, China: Bogota, Colombia; Beijing, China; and Toronto, Canada. However, the problem also concerns cities in the US—Los Angeles, New York, Chicago, Las Vegas and Milwaukee were the top five cities with the highest percentage of pediatric asthma cases linked to polluted air.

Susan Anenberg, senior author of the study, said: “Our findings suggest that millions of new cases of pediatric asthma could be prevented in cities around the world by reducing air pollution. Improving access to cleaner forms of transportation, like electrified public transport and active commuting by cycling and walking, would not only bring down NO2 levels, but would also reduce asthma, enhance physical fitness, and cut greenhouse gas emissions.”

The World Health Organization (WHO) calls air pollution “a major environmental risk to health” and has therefore established Air Quality Guidelines for NO2 and other air pollutants. The study findings suggest that the WHO guideline for NO2 may need to be re-evaluated to make sure it is sufficiently protective of children’s health.

For their study, the researchers used NO2 as a marker of the complex mixture of emissions from traffic. They believe that additional studies must be done to more conclusively identify the causative agent within this complex mixture.

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Author: Roberta Attanasio

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19 Comments

  1. There are several ways air pollution can be reduced to prevent and improve many asthma cases in children. I strongly agree that reducing NO2 levels can be achieved by increasing cleaner forms of transportation, specifically cycling and walking. This second article assessed and reported the “beneficial effects of increased physical activity are substantially larger (3–14 months gained) than the potential mortality effect of increased inhaled air pollution doses (0.8–40 days lost) and the increase in traffic accidents (5–9 days lost)”.

    Societal shifts from driving to cycling and walking will not only improve the air quality over time by reducing emissions, but it can also improve the individual’s health in various ways. The physical activity achieved from cycling and walking can help the body to flush out bacteria from the lungs and airways that are suppressing genes that differentiate harmful and dangerous bacteria, preventing an inflammatory response. There are several studies that support regular exercise having a positive effect on the immune system. Unfortunately reducing childhood asthma by decreasing air pollutants would require both time and efforts from the population at large. A societal shift this large will require community education and awareness on the harmful effects of pollution on the human immune system. This would likely also require a change in government policy promoting cleaner transportation and banning transportations that cause excessive emissions.

    (Article): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2920084/

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  2. Even though many emitted gases from trucks, cars, etc. are harmful to children’s respiratory systems, nitrogen dioxide is a key player to increasing cases of childhood asthma according to recent studies. My question is are there
    preventative methods that can be implemented before the development of asthma in highly concentrated polluted areas. Current evidence that suggests breast feeding can have short term and long term protective effects from air pollution exposure. It showed that children that were breastfed had a lower risk of developing asthma and that the duration of being breastfed also was related to the lower risk of developing asthma despite exposure. Breast milk is composed of long chains of unsaturated fatty acids, vitamins, antioxidants, immunoglobulins, and cytokines which contribute to its protective effects. Possible mechanisms suggest that when breast milk is ingested these components may reduce inflammation when exposed to pollutants and boost the immune system and that breast feeding is associated with better lung function. Because the time period these protective effects is still unknown, more research needs to be done to come to a conclusion. But, research has also suggested that women exposed to pollutants carry these pollutants in their system and this will carry on to the fetus and into a newborn child once breastfeeding starts. This suggests that in order for breastfeeding to be effective, reduction of air pollution, offering cleaner forms of transportation, etc. needs to be implemented while trying to use this type of preventative method. Obviously, further research needs to be conducted in order to be able to securely implement this preventative method, but based on current research it is possible.

    https://www.ncbi.nlm.nih.gov/pubmed/31671856

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    • That’s a very fascinating approach towards preventative methods of childhood asthma and more research should be done on that. I also took a similar approach and looked at diet and asthma. Although we generally associate things like obesity, type 2 diabetes and cardiovascular disease with diet it may also be a causal factor in asthma. Especially in the western world, the study mentioned that the western diet which is high in refined grains and processed red meats have pro-inflammatory effects which can contribute to asthma. Other diets such as a Mediterranean diet which is rich in fruits and vegetables may be more beneficial because its anti-inflammatory responses. More research needs to be done on possible nutrition therapy to aid in asthma treatments as diet can play a role in asthma.
      https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5707699/

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    • You bring up a good point, Genevieve.Your post intrigued my attention, and I could not help but add on to your comment. I found a study that questioned if breastfeeding associated with a lower risk of impaired lung function in children exposed to air pollution. Zhang Et. al, studied 6740 Chinese children aged 7-14 years. The children were breastfed for longer than three months. They found that exposure to greater air pollution increased the risk of developing lung function impairment. In breastfed children, there were fewer lung function impairments compared to children who were breastfed. This study shows the association between breastfeeding and decreased the risk of lung function impairment. I have to agree with you that further research should be conducted to encourage breastfeeding to all mothers.

      Link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6632134/

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    • Great post Genevieve, however, I respectfully challenge your point. Though breast milk has many healing properties because it contains essential compounds crucial for proper development of a child, it is also at risk for containing toxins and metals that the mother is exposed to. An article I found titled “The impact of environmental pollution on the quality of mother’s milk” states that breast milk is “a biofluid which can contain environmental pollution, which can have effects on immune system and consequently on the various body organs”. In the article, they studied polychlorinated biphenyls which are organic pollutants which have been detected in human milk and other dangerous pollutants found in breast milk. These polychlorinated biphenyls “have lipophilic properties, so they can penetrate to fatty milk and ultimately to neonate digestive track”. Human milk also contains an alarming amount of heavy metals such as arsenic, lead, cadmium, and mercury. These heavy metals in a certain concentration were shown to cause immunological disorders which correlates to health problems in children such as “allergy, disorders in the endocrine system, end even neurodevelopment delay and disorder”, more specifically, exposure to metals like arsenic in contaminated breast milk to newborns can cause an increase in asthma development. With the conclusion from your supported article and mines, it seems as though breast feeding can lead to a decrease in asthma and other immunological diseases only if the mother has been exposed to a low level of metals and dioxins/other pollutants. More research is needed to form an accurate conclusion pertaining to the immune system and breast milk in a developing offspring.

      https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6447517/

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      • A lot of good points here. It is a complex problem to try to deal with, but piece-meal reduction in pollutant exposures, while important to do, just will not get the job done as fast as needed for the masses of folk harmed and the vast number of contaminants at given sites. And exercise, to reduce harmful effects would be beneficial of course, but only if the exercise were done elsewhere where there were far fewer pollutants. Exercise increases respiration rates, which greatly increases the amount of pollutants entering the lungs. I’m afraid that as long as people stay trapped within the high risk environments, with high air pollution concentrations, It may just be that exercise often just makes things worse too frequently. Many urban environments are probably just too polluted to be able to expect that these areas can readily be cleaned up enough fast enough. Migration needs to be kept in mind as an important option for those lucky folk with the means available to move to far less polluted sites. And, very regrettably not a good option for far too many folk, thus the rich get richer and the poor get poorer relentlessly.

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  3. The World Health Organization calls air pollution “a major environmental risk to health” this statement is very accurate. My question is how disturbing would air pollution affect prenatal during pregnancy. Would the air pollution affect the newborns with respiratory attacks, or would the newborns be immune to the pollution that would not affect their breathing. Rosa mentioned in this article, they are supporting evidence that links the early life asthma development. I believe that effects of stress in pregnancy and during early development on the onset of asthma-related phenotype across childhood. According to the article, maternal anxiety or depression increase the risk for childhood respiratory disorders. Changes is necessary to prevent chronic respiratory disease such as improving transportation this will help reduce the amount of NO2 in the air this will benefit children growing up and preventing respiratory disease.

    https://www.ncbi.nlm.nih.gov/pubmed/29369067

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    • Great line of thinking Niyati! I too was interested in the effects on genetics. A study by Gregory et. al. showed that there is indeed a transgenerational effect (in mice models). Just a SINGLE exposure of diesel exhaust particles on pregnant mice showed an effect, not just on their offspring (F1 generation), but also the F2 and (to a lesser degree) F3 generation. The offspring had greater susceptibility to asthma (demonstrated by elevated eosinophil counts, and increased levels of IL-5 and IL-13.)

      https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5582941/

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    • Thinking on the same line as you, I was curious if its possible for mothers to confirm protection to their children through breastfeeding. We have read about antibodies from the breast milk being beneficial for the child and I was curious if they can help to protect children from asthma due to pollution. I was pleasantly surprised to find that the answer is yes!

      In a 2019 cross-sectional study of over 6000 Chinese children exposed to pollution, researchers compared lung function in children who had been breastfed for longer than 3 months versus those who were not. An electronic spirometer was employed to assess lung function. They found that in children who were not breastfed, they had approximately one interquartile range higher forced vital capacity (FVC) and also impairment in forced expiratory volume during the first second of exhalation. Children who were not breastfed also had higher incidents of coughing, wheezing, and asthma diagnosis. This protection does seem to decline as the child gets older.

      https://www.ncbi.nlm.nih.gov/pubmed/31125097

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      • I completely agree with the above comment. In accordance with that there was another study carried out which negate with the comment. A study conducted in China showed that children with normal birth rate and without any maternal disease during pregnancy, the factor of male sex, high birth rate and father smoking status all increased the risk of asthma. Also unlike exclusive breastfeeding, breast plus formula feeding increased fair risk but pure formula had opposite effects.

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  4. As mentioned in the article, the researcher considered nitrogen dioxide as a marker or the main causative agent in causing childhood asthma. My question is that how this is validated that nitrogen dioxide is the main player. One cohort study in Korea studied the interaction between environmental factors and the host factor alleviates the asthma severity. It is important to evaluate the factor associated with greater asthma severity in children. In their study, they included 667 children and they were diagnosed with the basic symptoms. They showed that the prevalence of mild persistent asthma was highest followed by mild intermittent asthma and severe persistent asthma. A history of bronchiolitis in the infant was inversely associated with greater asthma severity. No usage of an air purifier during exposure to high levels of outdoor air pollution showed a decreasing trend. It was showed a factor affecting the greater likelihood of severe asthma was exposure to ETS. The positive association between current exposure to ETS which result in greater asthma severity. Hence, there can be different markers associated with asthma severity and an early onset of childhood asthma and which need to be addressed.

    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4465283/

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    • I completely agree with your thoughts. I found an interesting article that studied the number of childhood asthma cases in 609 different families from 4 urban areas. It concluded that “asthma in the US appears to more frequent in ethnic minorities and in children growing up in poor urban neighborhoods and is least common in rural areas in combination with farm animal exposure”. The participants resided in Baltimore, Boston, New York, and St. Lewis. I would be very interested to read about studies comparing the percent of children with asthma from different countries. The US is not as strict as other countries when it comes to pollution emissions. I would love to see if there is an increase in children with asthma in the US than there is in a cleaner country with tighter control on their emission standards.
      (Article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2860857/)

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  5. From this post, it’s clear that NO2 doesn’t seem to do anything positive for the lungs, especially in asthmatic individuals. Diving deeper into what NO2 does once it enters the lungs is even more evidence as to why it’s such a harmful inhaled chemical. A study looked into pro-inflammatory cytokines taken from normal human bronchial epithelial (NHBE) in vitro and exposed them to a brief high concentration to of NO2 were assessed. The cytokines that were looked into were: IL-8, TNF-a, IFN-g and Il-1B. The cells were treated with these pro-inflammatory cytokines alone or in combination with NO2 and it showed an increase in TNF-a and IFN-g causing increased cell death by 28-36%, and it also showed that IL-8 may have a more synergistic role of inflammatory mediators. This may suggest an increased sensitivity of cytokines in response to NO2. Since the cytokine response to air pollution is an important role in people who have healthy lungs, but these cytokines may seem more harmful to people who have asthma, since one of the main problems of asthma is a response to air pollutants triggering an IgE response with an increased release of cytokines in the lungs. We already have drugs on the market that help with asthma such as the monoclonal antibody “omalizumab” and how it interacts with IgE and FcεRI and FcεRII on mast cells, so my question is should we research and target the over production of pro-inflammatory cytokines within asthmatic individuals, or try to inhibit the cytokines that are released during an asthmatic response? Would this type of immunotherapy be a positive or negative benefit, since the balance of cytokines within the body are extremely important? Because too much or too little of certain cytokines can cause massive problems within the body.

    Article:
    https://www.ncbi.nlm.nih.gov/pubmed/15003325

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  6. It was mentioned in the article that air pollution suppresses the genes that regulate the immune system’s ability to differentiate harmless substances from viruses or bacteria. My question is: would these changes be permanent from generation to generation? What if a child who was born in a heavily polluted area, and then were transferred to a new area with better air quality, how would they do? My guess is that physiologically their lungs would improve without the particulate matter in the air, but I am unsure about if the epigenetic effects would linger, and possibly be transferred to another generation. Epigenetic mechanisms control gene expression without affecting the DNA sequence itself, e.g. DNA methylation (which leads to inactivation) or histone modifications. They may also affect post-transcriptional gene regulation via alternative splicing, or microRNA. Epigenetics can be tricky because sometimes all these patterns (such as methylation) are wiped out (i. e. reprogramming) or sometimes they’re left in.
    For example, a study in Italy showed that steel workers sustained DNA damage just hours after exposure to air pollutants. This damage showed methylation of genes thought to be tumor suppressors. Damage is immediate, but is it long lasting? How does this relate to immunity? In 2012 Patricia Silveyra and Joanna Floros reported that lung alveolar type II cells (specifically SP-A) are altered in several diseases such as cystic fibrosis and pneumonia (leading to a susceptibility to environmental air pollutants). SP-A has been shown to enhance phagocytosis, attract alveolar macrophages to the site of infection, induce proliferation of immune cells, modulate the generation of reactive oxygen species, and stimulate pro-inflammatory cytokine production. We know that an over-reaction of cytokines and inflammation is associated with asthma. To bring this all together, environmental effects such as particulate matter, cigarette smoke, and ozone, all affect epigenetics. Epigenetics then affects SP-A expression, which affects the innate immunity.

    Article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3601480/

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    • I liked your approach on how air pollution can affect the epigenetic side of the lung immune system, and I would theorize that it is probably one factor of many that affects the lung immune system. A study was done on animals who inhaled varying amounts of NO2 for different amounts of time of exposure. A single exposure of high NO2 concentration for 5-6 hours produced intense cellular proliferation, but would regress after 48 hours in all parts of the lungs, except for the bronchiole and alveoli, which would last 4-7 days. These are also the main areas that are affected in asthmatic patients. Long exposure of lower amounts for 20-22 hours for a 7 days/week, would lead to a much longer period of tissue recovery (3+ months after exposure removal). Phospholipids are protein synthesis were depressed, Lecithin was increased, synthesis of proteases from lung macrophages were increased when exposed to NO2, and mirrored the lung macrophages found in smoker’s lungs.

      My interpretation of this is that it the lung microenvironment is definitely affected from air pollutants, but it seems like the tissue will eventually heal itself, so your comment about: “What if a child who was born in a heavily polluted area, and then were transferred to a new area with better air quality, how would they do?” From this paper, it seems like they could possibly benefit from moving out of the dirty air quality of the city and moving to a cleaner air environment. It seems that the tissue is always fighting an uphill battle of trying to repair itself, since were constantly exposed to it and that you can possibly remove yourself from the environment and actually start to heal damaged tissue. However, it may take a long time to recover depending on the constant rate and length of exposure to air pollutants

      Article:
      https://www.ncbi.nlm.nih.gov/pubmed/844614

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  7. Childhood asthma has become a major issue and is rising with traffic-related air pollution from automobile emissions. Many studies have been done researching health effects on childhood asthma and traffic-related air pollution, but not much research has been done on childhood school commute. Its estimated that more 25 million American children commute via diesel-powered school buses and therefore experience elevated pollution levels contributing to traffic-related air pollution. The U.S Environmental Protection Agency (USEPA) passed some legislation to reduce the sulfur levels in diesel fuel and also sparked a retrofit initiative to install cleaner air technologies in school buses. Those policies of implementing cleaner air technologies have reduced particle emissions by an estimated 20-50%. The study also illustrated that lower in-vehicle exposures and improved pulmonary health of children that rode on school buses that adopted the cleaner air technologies. Also, cleaner air technologies weren’t just associated with improved pulmonary health benefits but also reductions in on-board pollution. Using cleaner air technologies paired with cleaner commuting like cycling and driving green can help reduce traffic-related air pollution. Ultimately reducing the levels of Nitrogen dioxide (NO2) in the air, and reducing asthma levels.

    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4476560/
    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4083079/

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    • European birth cohort studies have examined the association between traffic-related air pollution and development of allergy and asthma in children. City with black smoke and NO2 were examined to provide exposure for young children developing allergy and asthma. The air quality has positive association between NO2 and causes asthma. This ties with your feedback to reduce sulfur levels in fuels to implement cleaner air technologies and could lead to improving the healthcare of children and reduce asthma level

      https://www.ncbi.nlm.nih.gov/pubmed/18079765

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  8. I found an article supporting this post that states, “current levels of air pollution are consistently associated with asthma development and morbidity among children, suggesting that current regulatory policies may be insufficient”. There are several ways air pollution can be reduced to prevent and improve many asthma cases in children. I strongly agree that reducing NO2 levels can be achieved by increasing cleaner forms of transportation, specifically cycling and walking. This second article assessed and reported the “beneficial effects of increased physical activity are substantially larger (3–14 months gained) than the potential mortality effect of increased inhaled air pollution doses (0.8–40 days lost) and the increase in traffic accidents (5–9 days lost)”.

    Societal shifts from driving to cycling and walking will not only improve the air quality over time by reducing emissions, but it can also improve the individual’s health in various ways. The physical activity achieved from cycling and walking can help the body to flush out bacteria from the lungs and airways that are suppressing genes that differentiate harmful and dangerous bacteria, preventing an inflammatory response. There are several studies that support regular exercise having a positive effect on the immune system. Unfortunately reducing childhood asthma by decreasing air pollutants would require both time and efforts from the population at large. A societal shift this large will require community education and awareness on the harmful effects of pollution on the human immune system. This would likely also require a change in government policy promoting cleaner transportation and banning transportations that cause excessive emissions.

    (Article 1): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2740858/

    (Article 2): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2920084/

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    • I agree with you totally.
      It is known that asthma attacks are triggered by multiple criteria pollutants, basides nitrogen dioxide (NO2) mentioned in the paragraph above, other factors such as particulate matter (PM), ozone (O3), sulfur dioxide (SO2), and carbon monoxide (CO) all can be triggers to cause asthma.
      Presently, short-term exposures to ozone, nitrogen dioxide, sulphur dioxide, PM2•5, and TRAP is thought to increase the risk of exacerbations of asthma symptoms. Increasing amounts of evidence also suggest that long-term exposures to air pollution, especially TRAP and its surrogate, nitrogen dioxide, can contribute to new-onset asthma in both children and adults.
      Young children with asthma, especially those growing up in economically disadvantaged neighbourhoods, are at increased risk of adverse effects from exposures to air pollution.
      Improved air quality to prevent exacerbations and new cases of asthma will require strong governmental efforts to move economies in both developed and developing countries away from combustion of fossil fuels for transportation and energy production; this approach is also needed to mitigate climate change.

      https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4465283/

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