January 21, 2020
Could air pollution contribute to memory decline and other symptoms of Alzheimer’s disease? New findings suggest it might.
The research, published in the journal Brain, looked at 998 women in their 70s and 80s who were free of Alzheimer’s disease or other forms of dementia at the study’s start. Researchers followed them for an average of 11 years.
The researchers, from the University of Southern California, found that women exposed to higher levels of air pollutants experienced greater declines in memory than their counterparts who breathed cleaner air. Women who breathed dirtier air also had more of the brain wasting, or atrophy, typical of Alzheimer’s disease.
“This is the first study to really show, in a statistical model, that air pollution was associated with changes in people’s brains, and that those changes were then connected with declines in memory performance,” said Andrew Petkus, assistant professor of clinical neurology at the Keck School of Medicine at USC. “Our hope is that by better understanding the underlying brain changes caused by air pollution, researchers will be able to develop interventions to help people with or at risk for cognitive decline.”
Little can be done at present to stop the progression of Alzheimer’s disease. Drugs may ease symptoms for a time, but do not stop the underlying disease process. And researchers still do not understand what causes Alzheimer’s disease.
This study found that tiny airborne pollutants called PM2.5 particles, which are about 1/30th the width of a human hair, were responsible for the brain changes. The particles are found in traffic exhaust and industrial smoke and are easily inhaled into the lungs, where they can enter the bloodstream and find their way into the brain.
Air pollution has already been tied to asthma, lung disease, heart disease and early death. These findings suggest they may also be bad for the brain.
For the study, researchers analyzed data from 998 women ranging in age from 73 to 87. All were part of a large study called the Women’s Health Initiative.
The women got regular MRI brain scans that looked for brain changes similar to those that occur in Alzheimer’s disease. None of the women actually had Alzheimer’s disease, though they showed varying degrees of memory decline during the course of the study. The researchers also had data about where the women lived and typical levels of air pollution in those areas.
When all that information was combined, researchers could see the association between higher pollution exposure, brain changes and memory problems. The researchers adjusted for such factors as differences in income, education, and whether the women smoked. They found that the greater the women’s exposure to PM 2.5 particulate, the lower their scores on tests of learning and memory skills.
It is difficult to establish a direct link between air pollution or other environmental toxins and a disease like Alzheimer’s, because so many factors are involved, and correlation does not equal causation. But “this study provides another piece of the Alzheimer’s disease puzzle by identifying some of the brain changes linking air pollution and memory decline,” Dr. Petkus said.
Earlier studies have suggested that exposure to polluted air contributed to the equivalent of about a two-year decline in brain function. Brain wasting might lead to an earlier onset of Alzheimer’s and other forms of dementia.
Animal studies have also recorded higher levels of brain inflammation in animals exposed to polluted air. Increasingly, scientists believe that inflammation may play a role in Alzheimer’s and heart disease.
By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Marc Flajolet, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.
Source: Diana Younan, Andrew J. Petkus, Keith F. Widaman, et al: “Particulate matter and episodic memory decline mediated by early neuroanatomic biomarkers of Alzheimer’s disease.” Brain, Nov. 20, 2019