Can air pollution increase your risk of dementia?

With wildfire season and the resulting air quality alerts upon many of us, air pollution has been prominent in the news and on people’s minds. Air pollution is clearly harmful for overall health, but can it also harm brain health?

The WHO estimates that 6.7 million people a year die prematurely because of air pollution [1]. Air pollution is linked to a variety of health conditions such as cardiovascular disease, respiratory issues, and cancer. Air pollution is also linked to dementia. In 2020, the Lancet Commission on Dementia Prevention, Intervention, and Care added air pollution to their list of twelve potentially modifiable risk factors for dementia that, if addressed, could collectively prevent or delay up to 40% of dementia cases [2].

The Lancet Commission findings have spurred research into the connections between air pollution and dementia. Four different meta-analyses, some including millions of patients, have been published in 2023 so far [3; 4; 5; 6]. The studies all found similar results: greater exposure to air pollution appears to be associated with a higher risk of dementia. Some studies have also found links between higher air pollution and faster rates of cognitive decline, both in healthy elderly adults and in patients with Alzheimer's disease [7; 8]. It appears that air pollution may be a particular risk for people who are carriers of APOE4, a genetic risk factor for Alzheimer’s disease [9].

There are many different kinds of air pollutants, though they are often produced from the same process: combustion of fuels, whether in cars, factories, or wildfires. Air pollutants include:

• Particulate matter: Particulate matter contains a mix of small particles, many smaller than the width of a human hair. Research indicates that exposure to these particles is particularly linked to cancer, heart disease, and dementia. Wearing an N95 mask can help block inhalation of and therefore damage from these particles. Air purifiers with HEPA filters can also help remove these particles from the air.
• Noxious gases such as carbon monoxide, sulfur oxides, nitrogen oxides, and ground level ozone (smog): These pollutants are associated with respiratory problems. Avoidance is the main way to protect yourself from these gases. Air purifiers with activated carbon filters may also help remove some of these gases from the air.

Air pollution is thought to increase risk of dementia in many ways. Some are indirect, such as by increasing risk of cardiovascular disease, which is also a risk factor for dementia. Air pollutants can also directly affect the brain. Different particles that make up air pollution can penetrate the brain and appear to cause brain changes that resemble dementia, as well as causing body-wide inflammation [10; 11; 12].

If you are concerned about your exposure to air pollution, there are concrete steps you can take to protect your health and your brain.

• Monitor air pollution levels, which vary locally, daily, seasonally, and even by time of day. You can do so online at sites like the EPA’s AirNow or with different apps. Consider staying indoors on days with particularly high air pollution. If you need to go outside on a day with poor air quality, wearing a well-fitting N95 mask or respirator can provide some protection from air pollutants. Cloth and surgical masks do not offer the same kind of protection for this health hazard.
• Protect your indoor spaces from outdoor air pollutants. Many outdoor pollutants such as fine particulate matter, ozone, and sulfate toxins can penetrate into buildings. Use portable (e.g., air purifiers) or central air cleaning systems to help reduce those levels [13].
• Control indoor air pollution sources. Do not allow smoking in your home or vehicle. Use an exhaust fan that vents outdoors while cooking and avoid using a wood stove or fireplace. More helpful tips can be found at public health resources like the EPA and NYC Health.
• Minimize exposure to car exhaust. Exposure to air pollution often peaks while driving in traffic. The California Environmental Protection Agency recommends that drivers close vents and windows while in heavy traffic with periodic air-outs to avoid build-up of CO2, 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 [14].
• Shift exercise routes away from high-traffic roads or other areas with higher air pollution —even moderate exercise can cause a 5-fold increase in the deposition of ultrafine particulate matter in the lungs. On days with poor air quality, exercise indoors if possible. If the option is to work out outdoors or not at all, then opt to work out. The benefits of exercise likely outweigh the risk of air pollution, for example, when commuting by bicycle along busy roads [15].

Air pollution can increase the risk of dementia, and researchers are working to better understand how air pollution affects brain health and how we can reduce air pollution and its deleterious effects. In the meantime, we can mitigate some of the personal risks through strategies like those listed above.

1. WHO (2022) Ambient (outdoor) air pollution.
2. Livingston G, Huntley J, Sommerlad A et al. (2020) Dementia prevention, intervention, and care: 2020 report of the Lancet Commission. Lancet  396, 413-446.
3. Wilker EH, Osman M, Weisskopf MG (2023) Ambient air pollution and clinical dementia: systematic review and meta-analysis. BMJ  381, e071620.
4. Abolhasani E, Hachinski V, Ghazaleh N et al. (2023) Air Pollution and Incidence of Dementia: A Systematic Review and Meta-analysis. Neurology  100, e242-e254.
5. Tang J, Chen A, He F et al. (2023) Association of air pollution with dementia: a systematic review with meta-analysis including new cohort data from China. Environ Res  223, 115048.
6. Gong Y, Zhang X, Zhao X et al. (2023) Global ambient particulate matter pollution and neurodegenerative disorders: a systematic review of literature and meta-analysis. Environ Sci Pollut Res Int  30, 39418-39430.
7. Kulick ER, Elkind MSV, Boehme AK et al. (2020) Long-term exposure to ambient air pollution, APOE-epsilon4 status, and cognitive decline in a cohort of older adults in northern Manhattan. Environ Int  136, 105440.
8. Lee YG, Yoon SJ, Yoon SH et al. (2023) Air pollution is associated with faster cognitive decline in Alzheimer's disease. Ann Clin Transl Neurol  10, 964-973.
9. Cacciottolo M, Wang X, Driscoll I et al. (2017) Particulate air pollutants, APOE alleles and their contributions to cognitive impairment in older women and to amyloidogenesis in experimental models. Transl Psychiatry  7, e1022.
10. Calderon-Garciduenas L, Avila-Ramirez J, Calderon-Garciduenas A et al. (2016) Cerebrospinal Fluid Biomarkers in Highly Exposed PM2.5 Urbanites: The Risk of Alzheimer's and Parkinson's Diseases in Young Mexico City Residents. J Alzheimers Dis  54, 597-613.
11. Schraufnagel DE, Balmes JR, Cowl CT et al. (2019) Air Pollution and Noncommunicable Diseases: A Review by the Forum of International Respiratory Societies' Environmental Committee, Part 1: The Damaging Effects of Air Pollution. Chest  155, 409-416.
12. Schraufnagel DE, Balmes JR, Cowl CT et al. (2019) Air Pollution and Noncommunicable Diseases: A Review by the Forum of International Respiratory Societies' Environmental Committee, Part 2: Air Pollution and Organ Systems. Chest  155, 417-426.
13. EPA Guide to Air Cleaners in the Home.
14. CaliforniaAirResourcesBoard Reduce Your Exposure to Particle Pollution.
15. Salmond JA, Tadaki M, Vardoulakis S et al. (2016) Health and climate related ecosystem services provided by street trees in the urban environment. Environ Health  15 Suppl 1, 36.

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