Effects of Pollution - Part 3

Part 1 of this series titled When Breathing is Bad for You explained how air quality is measured and the effects of air pollution on mortality. Part 2 described its effects on the fetus, the DNA damage incurred and the effects on the cardiovascular and respiratory systems. Part 3 continues the list of other effects of air pollution.

Ischemic stroke

While pollutants such as NO2, CO, O3 and SO2 did not have a significant effect, PM 2.5 did. Within hours of exposure to PM 2.5 levels considered safe by the EPA, the risk of ischemic stroke rises.1 The risk is not affected by co-morbid conditions including history of stroke, heart attack, atrial fibrillation, hypertension or age.

Cognitive ability

A study that examined both the cumulative and transitory exposure to air pollution found that long-term exposure negatively affected cognitive performance in both verbal and math tests.2 The decline was particularly noticeable in the elderly and especially so in less educated men.

Another study3 found that air pollution accelerated cognitive decline. Higher than usual levels of long-term exposure to particulate matter (PM 2.5 -10 and PM 2.5) caused a decline in cognitive function that was equivalent to aging by up to 2 years. The authors projected that a reduction in exposure to PM could delay the onset of Alzheimer’s disease by 2 years and consequently reduce the prevalence of cases by about 2 million over a 40 year period.

A Canadian study found that living near major roads adversely affect cognition.4 After adjusting for confounding factors such as socioeconomic status, education, body mass index, diabetes and brain injury, the study authors found that there was an association between distance to major traffic roads and an increased risk of dementia. It showed that the hazard ratio of incidence for dementia increased the closer they were to a major traffic road when compared with people who lived more than 300 meters from the road.

Hazard Ratio Distance

1.07 less than 50 meters

1.06 to 1.08 50 - 100 meters

1.02 101 - 200 meters

1.00 201 - 300 meters

A more recent retrospective cohort study used data from primary care centers of over 130,000 adults between the ages of 50 and 79. Pollution data was linked to electronic health records and dementia diagnoses including that of Alzheimer’s and vascular dementia, identified. The researchers found a “positive association between residential levels of air pollution and being diagnosed with dementia” even after accounting for confounding factors.5 A more recent observational study of 130,978 adults in London, UK, noted a positive exposure-response relationship between air pollution and dementia, both Alzheimer’s and vascular dementia.6 Those results replicated the results of a Canadian study, finding that exposure to even low levels was associated with a higher incidence of dementia.7

Neurological Disorder

Anywhere from 600,000 to 1 million adults in the US suffer from Parkinson’s Disease (PD) and about 60,000 patients a year are newly diagnosed with PD. PD is a degenerative disorder of the central nervous system that affects motor control. A recent study by Shin and fellow researchers used a 12-year span of data from adults who were free of PD at the beginning of the study. They looked at PM, Nitrogen dioxide and ozone. All three were found to have a positive association with PD but it was PM2.5 that was significantly associated with the PD. For every interquartile increase (3.8 mcg/m3) of PM2.5 there was a 4% increase in the incidence of PD.8

Reduction in life expectancy

Particulate matter (PM) smaller than 2.5 microns are known to enter deep into the lung and into the blood stream with the attendant risk of strokes, heart attacks, cancer and respiratory diseases. Researchers have shown that PM shortens survival on average by a year globally. In heavily polluted countries, the risk of death is higher than in less polluted countries.9

Another study looked at the impact of air pollution and mortality rates by age. It found that the average age of a victim of air pollution was 78.9 years and the average loss in life expectancy was 9 to 11 years.10

Metabolic dysfunction

Three major air pollutants, PM, nitrogen dioxide and NOx have been linked to metabolic dysfunction and an increased risk of Type 2 diabetes mellitus in both children and adults.11 A systemic review of recent studies also confirmed the association between air pollution and Type 2 Diabetes with the association stronger in females than males. It has also been shown to worsen diabetes and is associated with increased morbidity and mortality.12

Recent analysis of data from 1.7 millions US veterans has linked current ‘safe’ levels of outdoor air pollution to an increased risk of diabetes. This study from Washington University found a significant link between air pollution and diabetes even at low levels. It is thought to reduce the production of insulin and trigger inflammation thus preventing the conversion of blood glucose to energy – a requirement for maintaining health. The researchers estimated that air pollution results in 150,000 new cases of diabetes annually in the US with a resultant annual loss of 350,00 healthy years of life. They noted that the EPA’s safe level is 12 mcg/m3 of air yet they found a increased risk of diabetes at 2.4 mcg/m3. Risk levels for the development of diabetes were found to be 21% at 5 -10 mcg/m3 and increased to 24% at 11.9 to 13.6 mcg/m3.13


Air pollution has been linked to various cancers. A meta-analysis of over 300,000 members over a period of about 12 years found a statistically significant association between and air pollution and lung cancer. In studying the effects of long-term exposure to air pollution the researchers found that it was PM that contributed to the incidence of lung cancer.14 The Danish Diet Cancer and Health cohort provided data on the effects of NOx on over 54,000 participants for 10 years. It was found that residential NOx significantly increased the risk for brain cancer (RR2.28) and cervical cancer (RR 2.45).15 Air pollution also significantly increases the risk of lung cancer in non-smokers, particularly women. 16 PM and ozone have also been linked to an increased risk of mouth cancer.17

Economic costs

In the USA, a cost-benefit analysis was used with an estimate of every life saved being worth $7.4 million. Thus the associated economic costs of reduced life-expectancy is in the billions.10 There is the additional economic impact of reduced life expectancy, chronic disease, impaired work performance and resulting absence from work, all of which are considerable.

There are also costs incurred through increased emergency room(ER) visits. A recent USA study18 on air pollution and respiratory ER visits noted the effect of air pollution on patients of all ages. Previous studies emphasized the effects of air pollution on children and on the elderly. This study divided patients according to age – under 19, under 65 and over 65. The study showed an association between pollutants such as ozone and fine paniculata matter and ER visits for asthma, COPD, pneumonia and acute respiratory infections with the strongest association for asthma in adults under 65.

For every 10ppb increase in ozone the increase for children, adults and adults over 65 in ER visits was 1.7%, 5.1% and 3.3% respectively. For every 10mcg/m3 increase in PM 2.5 the respective increases were 2.4%, 0.8% and 0.02%.

Air pollution places a large burden both medically and economically on the population. Its costs on the individual’s health and quality of life, is reducible, though not completely avoidable. Thus, individuals with respiratory disease and others who are at risk should be warned of the dangers inherent in increased levels of air pollution. Information on local pollution levels is widely available on the Internet, television, newspapers and radio. Awareness is the key to health and in these times of major weather events and increased pollution, knowing what to do and when to do it can literally save lives.


CO carbon monoxide, COPD chronic obstructive pulmonary disease, FeNO fraction of exhaled nitric oxide, FEV1 forced expiratory volume in one second, FVC forced vital capacity, mcg/m3 micrograms per cubic meter, Nox nitric oxides, O3 ozone, ppb parts per billion, PM particulate matter 2.5 mcg, PAH polycyclic aromatic hydrocarbons, RR relative risk, SO2 sulphur dioxide


  1. Wellenius GA, Burger MR et al. Ambient air pollution and the risk of acute ischemic stroke. Arch Intern Med. 2012;172(3):229-234. doi:10.1001/archinternmed.2011.732

  2. Zhang Xin, Chen Xi, Zhang X. The impact of exposure to air pollution on cognitive performance. https://doi.org/10.1073/pnas.1809474115

  3. Weuve J, Puett RC et al. Exposure to particulate air pollution and cognitive decline in older women. Arch Intern Med. 2012;172(3):219-227. doi:10.1001/archinternmed.2011.683

  4. Chen H, Kwong JC et al. Exposure to ambient air pollution and the incidence of dementia: a population-based cohort study. Environ Int 2017;108:271–7.doi:10.1016/j.envint.2017.08.020

  5. Carey IM, Anderson HR et al. Are noise and air pollution related to the incidence of dementia? A cohort study in London, England. BMJ Open 2018;8:e022404. doi: 10.1136/bmjopen-2018-022404

  6. Carey IM, Anderson HR et al. Are noise and air pollution related to the incidence of dementia? A cohort study in London, England. BMJ September 2018 https://bmjopen.bmj.com/content/8/9/e022404

  7. Chen H, Kwong JC et al. Exposure to ambient air pollution and the incidence of dementia: A population-based cohort study. Environ Int. 2017 Nov;108:271-277. doi: 10.1016/j.envint.2017.08.020.

  8. Shin S, Burnett RT et al. Effects of ambient air pollution on incident Parkinson's disease in Ontario, 2001 to 2013: a population-based cohort study. Int J Epidemiol. 2018 Aug 16. doi: 10.1093/ije/dyy172.

  9. Apte JS, Brauer M et al. Ambient PM2.5 reduces global and regional life expectancy. Environmental Science & Technology Letters, 2018; DOI: 10.1021/acs.estlett.8b00360

  10. Mikael Skou Andersen. Co-benefits of climate mitigation: Counting statistical lives or life-years? Ecological Indicators, 2017; 79: 11 DOI: 10.1016/j.ecolind.2017.03.051

  11. Alderete TL, Chen Z, et al. Ambient and traffic-related air pollution exposures as novel risk factors for metabolic dysfunction and type 2 diabetes. Curr Epidemiol Rep. 2018 Jun;5(2):79-91. doi: 10.1007/s40471-018-0140-5

  12. Eze IC, Hemkens LG et al. Association between ambient air pollution and diabetes mellitus in Europe and North America: systemic review and meta-analysis. Environ Health Perspect. 2015 ;123(5):381-9. doi: 10.1289/ehp.1307823

  13. Bowe B, Xie Y, et al. The 2016 global and national burden of diabetes mellitus attributable to fine particulate matter air pollution. The Lancet Planetary Health, July 2018. DOI:https://doi.org/10.1016/S2542-5196(18)30140-2

  14. Raaschou-Nielsen O, Andersen ZJ, et al. Air pollution and lung cancer incidence in 17 European cohorts: prospective analyses from the European Study of Cohorts for Air Pollution Effects (ESCAPE). Lancet Oncol. 2013 Aug; 14(9):813-22.

  15. Raaschou-Nielsen O, Andersen ZJ, et al. Air pollution from traffic and cancer incidence: a Danish cohort study. Environ Health. 2011 Jul 19;10:67. doi: 10.1186/1476-069X-10-67.

  16. Air Pollution Increases Lung Cancer Risk in Nonsmokers - Medscape - Sep 25, 2018.

  17. Chu Y, Kao S et al. Association between fine particulate matter and oral cancer among Taiwanese men. Journal of Investigative Medicine, 2018; jim-2016-000263 DOI: 10.1136/jim-2016-000263

  18. Stronsnider HM, Chang HH et al. Age-specific associations of ozone and PM2.5 with respiratory emergency department visits in the US. Am J Respir Crit Care Med, 2018; DOI: 10.1164/rccm.201806-1147OC