Is air pollution linked to a higher risk of dementia?

(CNN) – Scientists have known for a long time that breathing dirty air can be detrimental to your health, including the health of your brain.

Today, a study published Tuesday in the medical journal BMJ Open shows how exposure to high concentrations of air and noise pollution could be linked to an increased risk of dementia.

The study found that among London's seniors, people living in areas with the highest annual concentration of air pollution in the region were at higher risk of dementia compared to those living in areas where the quantity was the lowest.

Specifically, those who were in the fifth exposure group were "40% more likely to be diagnosed with dementia in the study" than those in the fifth, even after adjusting for dementia. other risk factors such as smoking or socioeconomic status. Senior Lecturer in Epidemiology at the Institute of Population Health Research at St. George University, London, lead author of the paper.

"Although the results should be treated with caution, the study is an important addition to the growing evidence of a possible link between traffic pollution and dementia," Carey said.

The study "should encourage further research to study this issue," he added.

According to the World Health Organization, dementia is the seventh leading cause of death in the world. The syndrome involves the loss of cognitive functioning and behavioral abilities, and Alzheimer's disease is the most common cause of dementia in the elderly.

In the United States, about 5.7 million Americans live with Alzheimer's disease, according to the US-based Alzheimer's Association. In the UK, approximately 850,000 people with dementia, according to the UK-based Alzheimer Society. According to WHO, the number of people with Alzheimer's disease and other dementias worldwide is estimated at 47 million, and is expected to increase to 75 million by 2030 and is expected to almost triple by 2050, according to WHO.

& # 39; We were surprised & # 39;

For the new study, researchers estimated the amount of air pollution in different areas around Greater London in 2004, using a modeling system called KCLurban. They also estimated noise levels of road traffic using a model called TRAffic Noise Exposure.

Next, researchers looked closely at diagnoses of dementia between 2005 and 2013 in a sample of 130,978 adults aged 50 to 79, whose various primary care practices and residential postal codes were in the US. Great London.

During the study, 2,181 adults or 1.7% in total were first diagnosed with dementia. The anonymous electronic health records for adults came from a non-profit government service called Clinical Practice Research Clinic.

Using their models, the researchers then estimated traffic noise and air pollutants, such as nitrogen dioxide from vehicles and power plants, as well as fine particles, a complex mixture of small particles. and liquid droplets. would have been exposed each year. The researchers ranked the postal code of each adult in fifths, based on the areas with the highest and lowest air and noise pollution.

After analyzing models of air pollution and noise as well as health records, the researchers found that patients with annual exposure to nitrogen dioxide in the fifth of exposures had a marked increase risk.

Even when independent risk factors for dementia – such as hypertension or obesity – have been taken into account, this association has remained.

"We were surprised to find a potential link with dementia, however, other recent discoveries, including a large study in Canada, have begun to report a possible effect of life near the main roads," he said. Carey.

The new study had certain limitations. "The main limitations of the study concern the uncertainty of exposure where we assume that traffic pollution levels to a person can adequately represent their long-term exposure." The under-diagnosis of dementia in patients' electronic files ".

The study was conducted only in London. Further research is therefore needed to determine if similar results could emerge in other parts of the world.

Overall, the study adds to a growing body of research on this potential link between air pollution and dementia.

Similar results in the United States, Canada and China

"It's probably the sixth or seventh serious regional study on air pollution and cognition that has been published in the last three years," said Caleb Finch, leading Alzheimer's disease specialist and professor. at the Leonard Davis School of University of California. Gerontology in Los Angeles.

Finch, who did not participate in the study, said the findings align with separate research that explored the links between air pollution and aging.

"They have a large population, and their conclusions are analyzed with the utmost care and perfectly in line with the overall conclusion, be it the United States, whether it is Ontario, Canada or China," she said. he declared.

This Canadian study, published last year in Environment International, found a positive association between fine particle exposure and the incidence of dementia in approximately 2.1 million seniors living in Ontario.

Finch co-directed a study, published last year in the journal Translational Psychiatry, which found a link between exposure to airborne particles and cognitive impairment in older women .

This study analyzed data on 3,647 women aged 65 to 79 in 48 states. The study also involved experiments conducted on animals.

In this study, the researchers found that residing in areas where the quality of EPA was above the norm was associated with an increased risk of overall cognitive decline and all-cause dementia, by 81% and 81%, respectively. 92%.

Another study, published last month in the Proceedings of the National Academy of Sciences, showed that long-term exposure to air pollution in China can hinder cognitive performance in verbal and mathematical tests.

For this study, researchers examined data from the National Longitudinal Survey of Chinese Family Panels, mapping the cognitive test scores of nearly 32,000 people aged 10 between 2010 and 2014 against the US. exposure to short- and long-term air pollution.

These researchers found that verbal and mathematical scores "decreased with increasing cumulative exposure to air pollution," with lower verbal scores being particularly pronounced among older, less educated men.

What is behind the link between pollution and dementia?

In general, additional research is needed to determine what might be the link between environmental factors such as air pollution and the risk of dementia and whether there is a cause-and-effect relationship, said Dr. Thomas Wisniewski, Director NYU Langone Health Cognitive Neurology Center in New York, which did not participate in the new study.

"It's just a very intriguing association, which is biologically quite plausible, but certainly requires further study in other populations," Wisniewski said.

"These environmental and lifestyle factors may account for one-third or more of the attributable risk," he said. "It is quite logical that various environmental and lifestyle issues may affect the prevalence and incidence of dementia and Alzheimer's disease."

In the end, Finch's lab is pursuing separate research on the specific mechanisms that underlie the association between air pollution and dementia, he said.

"My lab and several others are analyzing the mechanisms using rodent models," Finch said.

"Air pollution in a rodent model under highly controlled conditions increases the production of the toxic A-beta peptide, amyloid beta, which is a fundamental part of the neurodegeneration of Alzheimer's disease, which increases in the brain. ", he said.

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