Dirty air could increase your chances of dementia

By Cara Murez HealthDay Reporter

FRIDAY, April 7, 2023 (HealthDay News) — Exposure to air pollution may increase the risk of developing dementia, according to a review of previous research.

“There really hadn’t been, in my view, a good synthesis of all the data or all the literature that was out there and, in particular, the literature that included some of the more recent studies that involved a slightly different approach to do this study,” said the study’s co-author Marc Weisskopf. He is a professor of environmental epidemiology and physiology at the Harvard TH Chan School of Public Health, Boston.

The researchers scanned more than 2,000 studies in their review, finding 51 that examined an association between ambient air pollution and clinical dementia. These studies have been published within the last 10 years.

Sixteen studies met their criteria after assessing bias using what is called the risk of bias in non-randomised exposure studies (ROBINS-E). Weisskopf explained that with environmental exposure issues, biases can be subtle and don’t lend themselves to easy measurement. ROBINS-E allows for a more thorough assessment of the possibility of bias.

The meta-analysis found consistent evidence for an association between PM2.5 and dementia.

This was true even when exposure was below the current limit set by the U.S. Environmental Protection Agency (EPA) – 12 micrograms per cubic meter of air (μg/m3) – a level that the EPA announced that it could lower.

The researchers found a 17% increase in the risk of developing dementia for each 2 μg/m3 increase in average annual PM2.5 exposure.

Associations also existed between nitrogen dioxide and nitrogen oxide and dementia. For nitrogen oxide, there was a 5% increase in risk for every 10 μg/m3 of annual exposure. For nitrogen dioxide, this was a 2% increase in risk for each 10 μg/m3 increase in annual exposure.

Many theories exist as to why dirty air could increase the risk of dementia. This may simply be because pollution affects cardiovascular health and this in turn affects brain health.

Another theory involves the impact of inflammation. Pollution can act directly on nerve cells or other brain cells, Weisskopf said, interfering with general brain function.

Although smoking is considered a bigger risk factor for dementia than air pollution, it could still have massive population-level implications because everyone has to breathe, Weisskopf noted.

“It’s unclear what mechanisms lead to this connection, but it’s hypothesized that the very small pollutant particles enter our body and enter our circulatory system, which helps fuel the brain,” he said. Rebecca Edelmayer, senior director of science engagement for the Alzheimer’s Association. Edelmayer did not participate in the study.

She noted that the results should be interpreted with caution due to limitations when performing a “meta-analysis” of observational studies.

“These data show that there are many factors across the lifespan that can contribute to our risk of dementia, and that includes the environment. We can control some of these factors, like what we eat and how often we exercise, but some are more difficult to control on an individual level, like where we live and the quality of the air around us,” said Edelmayer said.

She called on federal and local governments, as well as businesses, to take action to reduce air pollutants.

Weisskopf said agencies like the EPA could use the findings because they support the public health importance of tougher pollution limits.

A big uncertainty is when pollution exposure matters most in terms of association with dementia, Weisskopf noted.

“Most of these studies looked at the year or a few years before the onset of dementia, but it could be earlier in life, it could be throughout life. And so until we understand that better, those numbers are going to fluctuate quite a bit,” he explained.

Americans could potentially reduce some of the pollution they absorb through the choices they make, said Dr. Afif El Hasan, a Kaiser Permanente pediatrician in Southern California and a volunteer medical spokesperson for the American Lung Association. El-Hasan was not involved in this study.

“Obviously we have to go out. As a pediatrician, I want people to exercise,” he said.

El-Hasan suggested being aware of pollution levels, noting that many cities and states have websites offering information on today’s air quality or even variations at different times of the day.

“If possible, and we know it’s not always possible, take a look and schedule outdoor activities for times when there is less pollution, especially if you have a lung disease or other issues,” he said.

Use a filter that purifies the air in the house, he said. Do not smoke.

If the world is an unhealthy place, it can not only make medical problems worse, but will also have an economic impact, El-Hasan noted.

“I just hope the study will remind everyone that we are very affected by the world around us. It’s not independent. These are long-term effects, and it can have devastating effects on our whole body,” he added.

The results of the study were published on April 5 in BMJ.

SOURCES: Marc Weisskopf, PhD, ScB, professor, environmental epidemiology and physiology, Harvard TH Chan School of Public Health, Boston; Afif El-Hasan, MD, pediatrics, Kaiser Permanente San Juan Capistrano Medical Offices, California; Rebecca Edelmayer, PhD, senior director, science engagement, Alzheimer’s Association, Chicago; BMJApril 5, 2023

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