A growing body of evidence demonstrates that air pollution is linked to an increased risk of dementia or Alzheimer’s disease.
Dementia affects roughly 50 million people worldwide, according to the World Health Organization (WHO).
Alzheimer’s disease, the most common cause for dementia, is an irreversible, degenerative neurological disorder that causes memory loss and cognitive decline. It makes up approximately 60–80 percent of dementia cases.
A new study from the University of California, Davis adds to the growing body of evidence demonstrating a link between traffic-related air pollution and an increased risk of age-related dementia, such as Alzheimer’s disease.
The researchers set up a mouse vivarium near a heavily used traffic tunnel in Northern California for their recently published study. They created this to simulate the pollutants that people would encounter while stuck in traffic.
“A fundamental difference between this research and earlier efforts,” according to Dr. Pamela Lein, a professor of neurotoxicology at the University of California, Davis.
“Experimental animal studies have been necessary to confirm causality since epidemiologic studies can give data indicating the intensity of connection between exposure and outcome but cannot demonstrate a cause-effect relationship,” she said.
“However, much of the published animal data so far has been criticized since the exposures utilized have not precisely replicated human exposures,” Dr. Lein stated. This is because the animals were exposed to a subset of the components that make up traffic-related air pollution, and/or because the animals were exposed to extremely high concentrations of traffic-related air pollutants, typically for short periods.”
The researchers experimented on male and female rats for up to 14 months, exposing them to either filtered or contaminated air. They took dirty air from the busy tunnel in real-time and provided it to the animals in its original state.
The rats were divided into two groups: those that expressed Alzheimer’s disease risk genes that are relevant to humans, and those that were wild-type rats.
This experiment was carried out on rats aged three, six, ten, and fifteen months. They used hyperspectral imaging and behavioral testing to quantify the manifestation of Alzheimer’s disease features.
The researchers discovered that chronic traffic-related air pollution accelerated and aggravated Alzheimer’s disease-related features in rats who were genetically sensitive to the disease. A similar impact was observed in wild-type rats.
Dr. Lein told MNT, “Our research indicated that traffic-related air pollution shortens the time to onset and lengthens the severity of disease in rats with genetic risk factors for Alzheimer’s disease.”
“Different exposure histories may contribute to the varied clinical profiles observed in individuals with comparable genetic backgrounds,” she explained.
Dr. Heather Snyder, the Alzheimer’s Association’s vice president of medical and scientific relations, told MNT that the researchers behind this study are “looking at what might be a mechanism, what might be the molecular underpinnings” that lead to the beginning of Alzheimer’s disease.
She stressed that it is too soon to predict how the findings may affect humans. “Alzheimer’s disease, and indeed all forms of dementia, are […] complex diseases, and there are certainly a variety of factors that contribute to a person’s risk,” Dr. Snyder stated.
“Is it the particulate matter, the gases, or a combination of the two? Is it more important to promote Alzheimer’s disease phenotypes with components from light-duty (most cars) or heavy-duty (trucks, including diesel trucks) vehicles? The answer to this question will be crucial for regulatory policymaking.”
Dr. Lein also stated that she and the other researchers working on this project are keen to learn how traffic-related air pollution affects Alzheimer’s disease symptoms. They also wish to understand more about sensitivity windows.
“Do traffic-related air pollution exposures throughout childhood produce brain changes that show as [Alzheimer’s disease] phenotypes later in life?” she wondered. “Or are just exposures [in] middle and late-life crucial for increasing risk? Or do you need to be exposed to traffic-related air pollution for the rest of your life to witness the impacts on your brain?”
Dr. Lein told MNT that the purpose of her research is to discover specific environmental factors linked to an increased risk of Alzheimer’s disease. After all, these are less difficult to resolve than hereditary risk factors.