New study explains how air pollution increases the risk of dementia
Low concentrations of air pollutants are associated with poorer health, and previous research has found a link between air pollution and dementia risk. Researchers at Karolinska Institutet, among others, have now investigated this connection. The study, published in the journal Neurology, contributes to a better understanding of the biological mechanisms that might explain why air pollution seems to increase the risk of developing dementia.
"There is a significant indirect effect of air pollution on dementia," says Giulia Grande, researcher at the Department of Neurobiology, Care Sciences and Society, Karolinska Institutet and the study's first author.
In the study, researchers at, among others, Karolinska Institutet, Danderyd Hospital, and Oxford University, UK, studied more than 2,500 adults, with an average age of 73 and living in central Stockholm, for up to 12 years.
The participants underwent clinical examinations and blood tests as well as extensive evaluations from doctors, nurses and psychologists.
Before the study began, the annual average levels of PM2.5 were calculated at the participants' home addresses. PM2.5 is a term used to describe very small airborne particles that can have adverse health effects.
70 percent increased risk
The results showed that very small increases in PM2.5 mean a 70 percent increased risk of developing dementia. At the beginning of the study, the researchers also looked at the level of two vitamin B-related amino acids, homocysteine and methionine, in the participants' blood. The researchers then examined whether these amino acids altered the risk of dementia related to air pollution.
The researchers found that the risk of developing dementia was partly due to an interaction between air pollution and homocysteine and methionine, respectively.
Protective amino acids
The role played by homocysteine was observed only in participants who had developed cardiovascular disease, while the protective role of methionine was probably independent of the development of cardiovascular disease.
"These amino acids played a role in increasing or decreasing the risk of dementia caused by air pollution," says Debora Rizzuto, the study's last author and senior researcher at the Department of Neurobiology, Care Sciences and Society, Karolinska Institutet. "This suggests that air pollution affects the development of dementia in several ways."
The next step in the research is to continue to map the mechanisms by which air pollution causes dementia.
"There is still a long way to go, but our results suggest that several pathways are in place to determine dementia risk linked to air pollution and this underlines the need for further research into the exact biological mechanism," says Giulia Grande.
The study was funded by, among others, the Ministry of Health and Social Affairs, the Swedish Research Council and the Swedish Research Council for Health, Working Life and Welfare. The researchers do not report any conflicts of interest.
“Association of long-term exposure to air pollution and dementia risk: the role of homocysteine, methionine and cardiovascular burden”, G Grande, B Hooshmand, DL Vetrano, AD Smith, H Refsum, L Fratiglioni, P Ljungman, J Wu, A Bellavia, K Eneroth, T Bellander, D Rizzuto. Neurology, online July 19 2023, doi: 10.1212/WNL.0000000000207656.