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Omega-3 fatty acid levels appeared to weaken the inverse relationship between ambient fine particle exposure and brain aging, a prospective cohort study showed.

Older women exposed to high levels of air pollution who had the lowest levels of long-chain omega-3 polyunsaturated fatty acid in their blood had smaller brain volumes than women with the highest omega-3 fatty acid levels, reported Ka He, MD, ScD, of Columbia University in New York City, and co-authors.

Exposure to particulate matter 2.5 microns or less in width (PM_2.5) was tied to lower brain volume. Higher omega-3 fatty acid levels attenuated inverse associations between PM_2.5 exposure and white matter volumes in the total brain and in frontal, parietal, and temporal areas (all P for interaction <0.05), He and colleagues wrote in .

"Fine particle matters are very small; PM_2.5, for example is 30 times smaller than the width of a hair," explained the study's first author, Cheng Chen, PhD, also of Columbia University.

"Because these particles are so tiny, they can enter through the respiratory tract directly into the blood circulation system," she told MedPage Today. "With the blood flow to the body, they can cause damage to other systems, including the brain."

Fish oil has been shown to "reduce the brain damage caused by exposures to other environmental neurotoxins, including lead and methylmercury," Chen said. "But, no study has examined whether fish oil offers similar protection against PM_2.5 exposure. That's why we started this investigation."

Earlier research also has shown that were linked to smaller brain volumes and worse cognitive performance.

In this study, He and collaborators looked at data from participants in the Women's Health Initiative Memory Study-Magnetic Resonance Imaging (WHIMS-MRI) study. The group included 1,315 women with an average age of 70 at baseline (1996-1999) who were dementia-free and who underwent structural MRI in 2005-2006. Nine of 10 participants were white.

From baseline blood samples, the researchers analyzed erythrocyte membrane fatty acid composition, defining omega-3 index as the sum of membrane docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA).

The researchers also assessed omega-3 fatty acid intake and fish consumption at baseline screening using a semi-quantitative food frequency questionnaire. Fish consumption was divided into fried and non-fried fish groups. The team defined omega-3 intake as the sum of DHA and EPA intakes from diet. Information about frequency of use and dosage of fish oil supplements was not available.

Participant addresses were collected prospectively at each clinic visit and updated at least biannually. These were geocoded and used in a model that incorporated Environmental Protection Agency data to estimate the 3-year average PM_2.5 exposure before the MRI.

After adjusting for potential confounders, the researchers found that women with higher levels of long-chain omega-3 polyunsaturated fatty acid in red blood cells had significantly greater white matter and hippocampus volumes. For each interquartile increment (2.02%) in omega-3 index, the average volume was 5.03 cm³ (P<0.01) greater in white matter and 0.08 cm³ (P=0.03) greater in the hippocampus.

Women living in locations with higher ambient PM_2.5 exposure had significantly smaller white matter volume. For each quartile increase in PM_2.5levels, average white matter volume was 11.52 cm³ smaller in women with lower levels of omega-3 fatty acids and 0.12 cm³ smaller in women with higher levels (P<0.0001).

Consistent results were found for dietary intakes of omega-3 fatty acid and non-fried fish, the researchers noted. The study had limitations, they acknowledged: most participants were older white women, and only exposure to later-life air pollution was assessed, not exposure across the lifespan.

Nonetheless, the findings "provide helpful insight regarding how healthy lifestyles, like healthy diet, could reduce the adverse effects of air pollution on cognitive decline and neurodegeneration," Chen said.

"Future laboratory studies may investigate the underlying mechanisms of how omega-3 alleviates the brain damages induced by PM_2.5," she added. "In addition, future clinical trials may demonstrate the effects of fish oil supplementation as one of the critical strategies for preventing PM_2.5-induced neurotoxicity."

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