Air pollution may increase the risk of dementia

In:It’s no secret that air pollution can contribute to a number of health conditions, including heart and respiratory disease. Less well known, it may also play a role in cognitive decline.

in a study published in BMJResearchers at Harvard’s TH Chan School of Public Health present what they call the “best estimate” of how much air pollution may contribute to dementia risk. Analyzing more than 50 studies that tracked air pollutants and the incidence of dementia, scientists found that the risk of dementia increased by 4% for an increase of 2 mcg/m3 of air particles per year. When they focused on more rigorous studies that actively followed people by regularly testing them for dementia, instead of retrospectively examining their electronic health records, that risk rose to 17% to 42%.

“This is based on evidence for the role of air pollution in dementia,” said Mark Weiskopf, professor of environmental health and epidemiology at the Harvard TH Chan School of Public Health and lead author of the study. a Lancet The 2020 report was the first to identify air pollution as a contributing factor to dementia, Weisskopf said. “In that report, it was remarkable that the experts had a hard time putting numbers on the risk, because there was no such data. That’s partly why we did this analysis. The more data we can provide to doctors to make them aware of this link, the more people will understand how pollution may contribute to dementia risk.”

Most of the research Weisskopf analyzed focused on the concentration of fine particles less than 2.5 micrometers in diameter (3% of the diameter of a human hair), which are the most dangerous to human health. The US Environmental Protection Agency currently sets 12 mcg/m3 (micrograms per cubic meter) as the acceptable annual standard, but announced in January that it plans to revise that standard to 9 to 10 mcg/m3. (The proposal is currently open for public comment before the agency sets its final policy.)

read more: Eye disease is another health problem associated with air pollution

It’s unclear how much of a difference it will make when it comes to the contribution of pollution to dementia, Weisskopf says, because the data show there’s no safe threshold below which the risk drops to zero. Even at lower particle concentrations, “it’s still a problem,” he says.

Exactly how airborne particles may contribute to dementia is not known, but experts have several leading theories. One has to do with how pollution affects the heart, and how heart health in turn affects the brain. The pathway connecting the two pathways involves inflammation; the particles can trigger inflammatory reactions in tissues such as the heart and lungs, and when the cascade is unleashed and left unchecked, brain cells also become vulnerable to inflammatory damage. There is also growing evidence that particles can directly affect brain cells and cause inflammation of the nerves in the brain. “Neuroinflammation is a good response and protects cells,” says Weisskopf. “But if it goes on too long, it can cause damage, and it’s one strong candidate to explain how pollution affects dementia risk.”

Even if the risk of dementia is not completely eliminated by reducing the concentration of pollutants in the air, it can still reduce the risk, so it is important that doctors begin to raise awareness of the possible role of pollution with their patients. “What we’re trying to do is give this more meaning,” Weiskopf says. “I hope this risk is more likely to be included [discussions about dementia] in the future.”

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