Danger in the Air: Does Pollution Raise Your Dementia Risk?

Does air pollution contribute to the risk of dementia? And if so, what steps can you take to protect yourself?

A recent study published in The Lancet suggests that living near a major roadway may raise the risk of dementia. Researchers found that residents in Ontario had about 7% higher risk of developing dementia if they lived within 50 meters of a major roadway [1]. This recent study joins several other reports associating higher exposure to air pollution—such as that from car exhaust—with higher risk of dementia [2-5] or lower average cognitive function in older adults (reviewed in [6]).

This was an observational study, so the researchers can establish an association but not a cause and effect relationship between air pollution and dementia risk. It's possible that people exposed to more air pollution share other similarities, such as socioeconomic factors, which could cause harm. The researchers did, however, try to control for such factors and found no explanation other than air pollution for their results [1][6]. It's important to consider that in controlled laboratory experiments, air pollutants have caused damage consistent with Alzheimer's disease and other dementias [7-10].

The World Health Organization estimates that air pollution contributes to approximately 2.6 million premature deaths each year, mainly from heart disease, stroke, lung cancer, and respiratory illness. Even relatively low exposure may shorten average lifespan by several months, based on studies in European and North American countries [11]. Research has shown that harmful pollutants such as sulfur-dioxide, nitrogen dioxide, ozone, carbon monoxide, and fine particulate matter (PM2.5) can penetrate and lodge deep within the respiratory tract. Resulting respiratory illness or damage to the cardiovascular system can cause chronic inflammation that might also lead to increased risk of dementia [8][12].

If you are concerned about your exposure to air pollution, there are things you can do to protect your health and your brain. The drastic step of moving away from a major road is not always feasible, particularly if it means leaving a community you enjoy. Other steps can help you monitor and reduce your exposure to air pollution.

• Monitor air pollution levels, which vary locally, daily, seasonally, and even by time of day. You can do so online, with apps, and even with wearable devices and indoor air quality monitors. Personal devices are not as accurate as the monitors used by the EPA and other organizations, but they can still provide useful information about how levels change over time. At least one device, the Foobot, monitors VOCs, PM2.5, and CO2 levels and can turn on air purifiers or send an alert to your phone when pollution levels are high.
• Consider staying indoors on days with particularly high air pollution.
• Protect your home and office from outdoor air pollutants. Many outdoor pollutants such as fine particulate matter, ozone, and sulfate toxins can penetrate into buildings [13]. Use portable or central air cleaning systems (PDF) to help to reduce those levels.
• Keep car exhaust at bay. Exposure to air pollution often peaks while driving in traffic. The California Environmental Protection Agency (PDF) recommends that drivers close vents and windows while in heavy traffic (but air out the vehicle periodically to avoid a build-up of carbon dioxide), install a high efficiency particle filter if possible, avoid long warm-ups and unnecessary idling, keep vehicles tuned and maintained, and consider an electric, hybrid, or other low-emitting vehicle.
• Shift exercise routes away from highly polluted areas—even moderate exercise can cause a 5-fold increase in the deposition of ultrafine particulate matter in the lungs. But don't avoid exercise. The benefits of exercise likely outweigh the risk of air pollution, for example when commuting by bicycle along busy roads [13].
• Control indoor air pollution sources. Use an exhaust fan that vents outdoors while cooking and avoid using a wood stove or fireplace. The California Environmental Protection Agency has other helpful tips.
• Do not allow smoking in your home or vehicle.

While these steps can help, your exposure to air pollution is still affected by others. The good news is that air quality can be improved even as industry expands. For example, average PM2.5 levels in the US declined by 37% from 2000–2015, based on EPA measurements. Technological innovation is helping to lower emissions and reduce pollution. New approaches to old ideas, such as more vegetation in urban planning, could help as well. While common tactics such as occasional trees have minimal influence, one model predicted that ambitious vegetation planting in street canyons could reduce street-level concentrations of pollutants by up to 60% [14][15].

 

1. Chen, H., et al., Living near major roads and the incidence of dementia, Parkinson's disease, and multiple sclerosis: a population-based cohort study. Lancet, 2017.
2. Oudin, A., et al., Traffic-Related Air Pollution and Dementia Incidence in Northern Sweden: A Longitudinal Study. Environ Health Perspect, 2016. 124(3): p. 306-12.
3. Kioumourtzoglou, M.A., et al., Long-term PM2.5 Exposure and Neurological Hospital Admissions in the Northeastern United States. Environ Health Perspect, 2016. 124(1): p. 23-9.
4. Wu, Y.C., et al., Association between air pollutants and dementia risk in the elderly. Alzheimers Dement (Amst), 2015. 1(2): p. 220-8.
5. Jung, C.R., Y.T. Lin, and B.F. Hwang, Ozone, particulate matter, and newly diagnosed Alzheimer's disease: a population-based cohort study in Taiwan. J Alzheimers Dis, 2015. 44(2): p. 573-84.
6. Power, M.C., et al., Exposure to air pollution as a potential contributor to cognitive function, cognitive decline, brain imaging, and dementia: A systematic review of epidemiological research. Neurotoxicology, 2016. 56: p. 235-253.
7. Weuve, J., Invited commentary: how exposure to air pollution may shape dementia risk, and what epidemiology can say about it. Am J Epidemiol, 2014. 180(4): p. 367-71.
8. Fougere, B., et al., Air Pollution modifies the association between successful and pathological aging throughout the frailty condition. Ageing Res Rev, 2015. 24(Pt B): p. 299-303.
9. Yan, W., et al., NO2 inhalation causes tauopathy by disturbing the insulin signaling pathway. Chemosphere, 2016. 165: p. 248-256.
10. Cheng, H., et al., Nanoscale Particulate Matter from Urban Traffic Rapidly Induces Oxidative Stress and Inflammation in Olfactory Epithelium with Concomitant Effects on Brain. Environ Health Perspect, 2016. 124(10): p. 1537-1546.
11. Pinault, L., et al., Risk estimates of mortality attributed to low concentrations of ambient fine particulate matter in the Canadian community health survey cohort. Environ Health, 2016. 15: p. 18.
12. Shah, A.S., et al., Short term exposure to air pollution and stroke: systematic review and meta-analysis. BMJ, 2015. 350: p. h1295.
13. Laumbach, R., Q. Meng, and H. Kipen, What can individuals do to reduce personal health risks from air pollution? J Thorac Dis, 2015. 7(1): p. 96-107.
14. Pugh, T.A., et al., Effectiveness of green infrastructure for improvement of air quality in urban street canyons. Environ Sci Technol, 2012. 46(14): p. 7692-9.
15. Salmond, J.A., et al., Health and climate related ecosystem services provided by street trees in the urban environment. Environ Health, 2016. 15 Suppl 1: p. 36.

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