Does Eating Fish Protect the Brain Against Air Pollution?

Moderate dietary intake of omega-3 polyunsaturated fatty acids in the form of one to two servings of fish weekly may help counteract the potential harmful effects of air pollution on the brain, a new study suggests.

Among older women living in areas with high levels of air pollution, brain shrinkage was greater among those with the lowest blood levels of omega-3 fatty acids than among their counterparts who had the highest levels.

"We found that higher blood omega-3 levels attenuated the toxicity of PM2.5 exposure on white matter volumes in elderly US women. Similar protection was seen for dietary intakes of omega-3 and nonfried fish," Cheng Chen, PhD, from Columbia University Irving Medical Center in New York City, told Medscape Medical News.

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

The study was published online July 15 in Neurology.

Preserving Brain Volume

Previous studies have suggested that long-chain omega-3 polyunsaturated fatty acids (LCn3PUFAs) reduce brain damage caused by exposures to various environmental neurotoxins, including lead, organic solvents, and methyl mercury.

However, until now, no study has examined whether LCn3PUFAs offer similar protection against the neurotoxic effects of PM2.5 exposure.

Chen's team investigated whether blood LCn3PUFA levels modify the association between PM2.5 exposure and brain structure using data from the Women's Health Initiative Memory Study (WHIMS).

Participants included 1315 women aged 65 to 80 years who were free of dementia at enrollment between 1996 and 1999. The women completed questionnaires about diet, physical activity, and medical history.

The researchers used the women's home addresses to gauge their average PM2.5 exposure over 3 years prior to undergoing structural brain MRI between 2005 and 2006.

After adjusting for multiple potential confounding factors that could affect brain volume, the investigators found that white matter and hippocampus volumes were significantly greater in women whose blood levels of LCn3PUFA were higher.

For each interquartile increment (2.02%) of omega-3 index, the average volume was 5.03 cm³ (P < .01) greater in the white matter and 0.08 cm³ (P = .03) greater in the hippocampus.

Higher LCn3PUFA levels attenuated the inverse associations between PM2.5 exposure and white matter volumes in the total brain and multimodal association areas (frontal, parietal and temporal; all P for interaction < .05).

Chen said, "Future laboratory studies may help elucidate the underlying mechanisms how omega-3 alleviates the brain damages induced by PM2.5 exposure, and clinical trials may demonstrate the effects of fish oil supplementation as one of the critical strategies for preventing PM2.5-induced neurotoxicity."

Experts Weigh In

Commenting on the results for Medscape Medical News, Lilly Jung Henson, MD, chief of neurology at Piedmont Healthcare in Stockbridge, Georgia, said this is "an ingenious look at the potential benefits of fish consumption on environmental risk factors for dementia.

"As you would expect from mining data from a large cohort like this, there is a fair amount of extrapolation and interpretation of data, but it's a great way on a macro level to sort out variables such as diet and environmental exposures that might influence brain health," said Jung Henson.

Also weighing in on the results, Katrina Hartog, RD, clinical nutrition manager, Lenox Hill Hospital, New York City, cautioned that data on supplemental use of fish oil were collected but data on frequency of use and dosage were not available.

"This is a major limitation, as many studies showcase this as a very effective way to increase omega-3 fatty acid intake," she told Medscape Medical News.

"More research is needed on the topic of what amounts of high omega-3 foods or fish oil specifically will mitigate exposure to environmental particle matter as related to brain and cognitive health," said Hartog.

"We know that higher consumption of omega-3 polyunsaturated fatty acids have positive impact on both brain and heart health. The Academy of Nutrition and Dietetics as well as the American Heart Association recommend eating fish twice per week to give you a heart-healthy amount of omega-3 fatty acids," Hartog said.

On the basis of these findings, individuals "should consider including more omega-3 fatty acid foods into their diets, and better yet, substituting these foods for red and processed meats. The best sources of omega-3's are herring, mackerel, salmon, flax seeds, and chia seeds," said Hartog.

The study was funded by the National Institutes of Health. Chen, Jung Henson, and Hartog have disclosed no relevant financial relationships.

Neurology. Published online July 15, 2020. Abstract

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