FRIDAY, July 21, 2023 (HealthDay News) -- Scientists have reported a link between air pollution and dementia risk, but they haven't had a good understanding of the mechanisms behind this association. Now, a new study provides some answers.

“In this study, we found that two types of vitamin B-related amino acids played a role in increasing or decreasing the risk of dementia caused by air pollution,” said Dr. Giulia Grande, co-author of the report recently published in the journal Neurology. She is a postdoctoral researcher at the Karolinska Institute in Stockholm, Sweden.

The study found that higher levels of these vitamin B-related amino acids may be linked to the risk of dementia associated with air pollutants called fine particulate matter, or PM2.5.

Researchers looked at this fine particulate matter and two amino acids, methionine and homocysteine.

Methionine is an essential amino acid involved in normal brain functions. It is found in foods such as meat, fish, dairy, beans and eggs.

Homocysteine is an amino acid produced in the cells that can be transformed to methionine through a reaction that requires vitamin B12 and folate. It is important for red blood cell formation and for healthy cell growth and function.

The study included more than 2,500 adults, average age 73, living in central Stockholm. Researchers followed them for up to 12 years using interviews, questionnaires and blood tests.

A total of 376 people in the study developed dementia.

Researchers calculated annual average levels of PM2.5 at the home addresses of the participants.

Those who developed dementia had an average exposure to PM2.5 pollution of 8.4 micrograms per cubic meter (µg/m3), compared to 8.3 µg/m3 for the people who did not develop dementia.

These annual average levels of PM2.5 were low compared to the average level of PM2.5 in the rest of Europe, which is 13.8 μg/m3.

Researchers found the risk of dementia increased by 70% for every one µg/m3 increase of PM2.5 exposure during the five years before the start of the study.

They also found that about half of the increased risk of dementia due to PM2.5 was due to an interaction between air pollution and high homocysteine levels or low methionine levels.

“Our results indicated that raised homocysteine levels and low methionine values played a role in determining the dementia risk related to air pollution, but also showed that a substantial direct effect of air pollution on dementia exists, suggesting that air pollution affects the development of dementia through multiple pathways,” Grande said in a journal news release. “This highlights the need for further research into the exact biological mechanisms behind the brain damage of air pollution."

The study included only the small Kungsholmen district of Stockholm, which is a limitation. Also, comparisons regarding air pollutants were limited.

More information

The U.S. Environmental Protection Agency has more on PM2.5.

SOURCE: Neurology, news release, July 19, 2023