For centuries, Alzheimer’s and related dementias — debilitating diseases that cause memory loss over time, particularly in the elderly — have caused grief and pain in millions of families around the world.

According to the Alzheimer’s Association, 6.7 million Americans are currently living with Alzheimer’s. By 2050, that number is expected to rise to nearly 13 million. While most of these cases exist in those aged 65 or older, about 200,000 Americans under 65 years old currently live with Alzheimer’s or other dementias.

Scientists have long been on the hunt for one root cause of Alzheimer’s and dementia, but what they’ve found instead is that a variety of factors can increase one’s risk for those diseases. Now, according to a 2021 research review, they can add air pollution to that list.

How Does Alzheimer’s Affect the Brain?

While it’s normal for the brain to shrink in size as one ages, the brain does not typically lose mass amounts of neurons when that shrinking occurs, according to the National Institute of Health.

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However, in cases of Alzheimer’s and other dementias, the brain undergoes a massive loss of neurons and neuronal connections — specifically those in the parts of the brain involved with memory. As time goes on, other portions of the brain are damaged, as well.

It’s important to note that Alzheimer’s is a specific type of brain disease that can be categorized as dementia. However, dementia is a more general term for brain deterioration that causes memory loss.

Risk Factors for Alzheimer’s Disease and Dementia

According to the Alzheimer’s Association, the most common risk factors for Alzheimer’s — as well as other ailments associated with the development of Alzheimer’s and other forms of dementia — are heart disease, diabetes, stroke, high blood pressure and high cholesterol.

Numerous studies indicate that brain health and heart health are heavily connected. The risk of developing Alzheimer’s seems to be increased in those who have suffered damage to the heart and its surrounding blood vessels. According to the CDC, the risk for “vascular dementia”, a type of dementia that results from a series of mini-strokes in the brain, can also increase due to bad heart health.

“A lot of the [risk factors] are the same risk factors for living a long and healthy life,” says Erin Bennett, a senior research associate at George Washington University. “One of the major risk factors [for dementia] is any type of cardiovascular disease prevention, so making sure your blood pressure is at a healthy level, making sure you don’t have diabetes, a good BMI, stuff like that [is important].”

While these risk factors are common for other diseases too, there are also certain risk factors that are specifically associated with dementia, including level of education.

“Making sure everybody is able to graduate high school would be really, really helpful,” says Bennett.

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On top of that, both hearing loss and repeated traumatic brain injury are also risk factors for dementia. The latter is a key reason why there is so much research surrounding the brains of former NFL players, according to Bennett.

How Air Pollution Increases Risk Factors for Dementia

Researchers have continued to make progress in determining risk factors for dementia. In 2021, further evidence emerged to suggest that air pollution — specifically, fine particles of matter in the air that have a diameter of smaller than 2.5 micromoles — can lead to dementia.

The 2021 review analyzed 66 different research articles, all of which were required to meet specific criteria in order to be included. According to the review, eligible articles measured the association between long-term, outdoor air pollution exposures and dementia-related outcomes in certain samples of adults.

The results of the review found that this particulate matter had far more adverse associations with dementia than any other air pollutant studied. In other words, it was the air pollutant most associated with dementia development.

It is these recent developments that has led many dementia researchers to recognize air pollution as a legitimate risk factor for dementia.

“There’s just been tremendous growth in this area, and I think that’s really what has sort of propelled different organizations to officially recognize air pollution as a modifiable risk factor,” says Bennett, one of the authors of the 2021 analysis research, who adds that the Lancet Commission on dementia added air pollution to their list of modifiable risk factors in 2020.

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Increased Risk of Dementia in Certain Populations

With certain areas of the planet dealing with more air pollution than others, it is possible that some populations face a higher risk of developing dementia and Alzheimer’s than others.

“Black people and Hispanic/LatinX people are at a higher risk for dementia and carry most of the dementia burden in the United States,” says Bennett. While it is not confirmed that higher risks are tied to air pollution, it is a possibility.

A 2021 study from the Keck School of Medicine at the University of Southern California found that data increasingly shows that elderly people living in areas with higher levels of fine particulate matter are more likely to develop dementia. The study also noted that Black and African American individuals were more likely to live in these polluted areas.

It’s also important to note that poorer communities, regardless of race, tend to be exposed to higher levels of air pollution, according to the American Lung Association. In the United States, air pollution inequality research often focuses on race, but worldwide, it focuses more on social class.

However, Bennett adds that not as much dementia data exists outside of the United States, so it’s not clear whether certain trends persist worldwide.

An Emerging Field of Research

While it may seem like plenty of research has been conducted on air pollution and its links to dementia, it’s a relatively new field, with most of the research coming in the last 15 years, according to Bennett.

“I think a lot of this research is focused on dementia prevention,” says Bennett. “We know that if we can delay dementia onset for like five years, we can reduce so much human suffering and so much caregiver burden across the world.”

The key to that may just be reducing air pollution, specifically this type of particulate matter. By doing so, dementia may become easier to treat, not only in the United States, but worldwide.

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