We know that air pollution is bad for our lungs and heart and that globally it reduces our life expectancy by more than two years — but that’s just the start of our pollution problems. Now, health advisers to the UK government concluded it can also be linked to dementia and cognitive decline — something scientists have been warning about for years, but couldn’t quite prove it until now.

The Committee on the Medical Effects of Air Pollutants (COMEAP) reviewed about 70 epidemiological studies and concluded that the evidence suggests a connection between exposure to air pollutants and an “acceleration of the decline in cognitive function often associated with ageing, and with the risk of developing dementia.”

The researchers said they couldn’t estimate the number of older people who had seen a mental decline linked to air pollution because of a scarcity of studies that might provide causal evidence. However, they mentioned a 2018 study that found that 60,000 of the 209,600 new cases of dementia in the UK alone every year could be due to air pollution.

“It’s known that air pollution can affect the heart and the circulatory system, including circulation to the brain. These effects are linked to a form of dementia (vascular dementia) caused by damage to the blood vessels in the brain. Therefore, we think it likely that air pollution contributes to mental decline and dementia,” the report reads.

Dementia and air pollution

Dementia is an umbrella term for a range of conditions that affect how the brain works, reducing the ability to remember, think, and reason. It affects especially older people and it gets more severe over time. Several lifestyles and health factors, such as smoking and high blood pressure, can raise the risk of developing dementia.

In recent years, there has been growing interest in the possibility that exposure to outdoor air pollution could increase the risk of dementia. Studies from several countries have tried to find links between the two, measuring fine particulate matter in the brain and the body. However, the evidence hasn’t been fully conclusive so far, despite tantalizing clues.

The new report in the UK found three ways through which air pollution could be accelerating mental decline. The main one is the damage caused to the blood vessels by small particulate matter, which can affect the blood supply to the brain. In fact, there are several human studies showing the effect air pollution can have on blood vessels.

Other explanations, although more tentative, include the brain’s immunological system being activated after exposure to air pollution and the small particles reaching the brain through the nasal passage and the olfactory bulb. Evidence for these mechanisms is slimmer, and the committee is more confident in the blood vessels hypothesis.

Air pollution is made up of different components, such as gases, metals, chemical compounds and small particles known as particulate matter. Long-term exposure or exposure to high levels of air pollution can be very dangerous. The effects of air pollution are associated with seven million premature deaths per year, the WHO also mentions.

The full report by the committee can be accessed here.