Older women who ate more than 1-2 servings of fish or shellfish per week had greater volumes of white matter than those who had a low intake of fish. The findings suggest that omega-3 fatty acids, which can be easily sourced from fish and shellfish, may counteract the effects of air pollution on the brain.

Previous research has shown that omega-3 fatty acids relieve inflammation and help conserve brain structure in aging individuals.

Omega-3 also reduces brain damage due to neurotoxins such as lead and mercury. However, many toxins found in noxious fumes and other air pollution can also have a neurodegenerative effect on the brain. Could omega-3 offer protection against air pollution too? This is what researchers at Columbia University set out to investigate.

“In previous studies, fish oil reduced the brain damage caused by exposures to various environmental neurotoxins, including lead, organic solvents, and methyl mercury. PM_2.5 exposure (particulate matter smaller than 2.5 microns) is a risk factor for cognitive decline and reduced brain volumes. But, no study has examined whether fish oil offers similar protection against PM_2.5 exposure. Thus,  we started this investigation in the Women’s Health Initiative Memory Study (WHIMS) study. We found that higher blood omega-3 levels attenuated the toxicity of PM_2.5 exposure on white matter volumes in elderly US women. Similar protection was seen for dietary intakes of omega-3 and non-fried fish,” Ka He, a researcher at Columbia University in New York and lead author of the new study, told ZME Science.

For their study, 1,315 women with an average age of 70 and no prior history of dementia at the start of the study, had to fill in a questionnaire about their diet, physical activity, and medical history.

“Elderly people are in higher risk of cognitive decline and neurodegeneration, compared to younger adults. Increasing evidence in elderly populations supports that ambient air pollution, including PM_2.5 exposure, may be a novel environmental risk factor for cognitive impairments. Therefore,  we identified the WHIMS cohort as a well-characterized and geographically-diverse population unique for our research questions with comprehensive data on omega-3, PM_2.5, and MRI scanning,” He wrote in an email.

From their dieting data, the researchers calculated the average amount of fish each woman consumed on a weekly basis. This includes broiled or baked fish, canned tuna, tuna salad, tuna casserole, and non-fried shellfish. Fried fish and shellfish were not taken into account due to research showing deep-frying destroys the omega-3- fatty acids.

Blood was also drawn from the subjects in order to measure the amount of omega-3 fatty acids in their red blood cells. Based on their omega-3 fatty acids serum content, the participants were divided into four groups.

In order to assess air pollution exposure, the women’s home addresses were compared to three-year average measurements of air pollution in their respective areas.

Finally, all participants underwent brain scans with magnetic resonance imaging (MRI) in order to measure the structural health of various areas of the brain, with a focus on white matter and the hippocampus (the part of the brain responsible for storing and processing memory).

After adjusting for age, education, and other environmental factors, the team of researchers found that the women with the highest levels of omega-3 fatty acids in their bloodstream also had a greater volume of white matter when compared to those with the lowest levels. The average difference in brain volume between the two groups was 7 cubic centimeters.

Additionally, women with the highest levels of omega-3 fatty acids in the blood showed greater hippocampus volumes.

It’s important to note that the findings uncovered an association between brain volume and eating fish. This correlation does not prove any cause and effect relationship, although the researchers have some ideas.

“White matter may be a novel target of PM_2.5 neurotoxicity. On the other hand, omega-3 protects the cells responsible for the production and maintenance of myelin in the white matter. They can also help resolve local inflammation and promote remyelination in the white matter, thereby facilitating white matter repair. Therefore, high levels of omega-3 may alleviate myelin damage and the subsequent white matter abnormalities induced by PM_2.5 exposure,” He said.

It’s also not a good idea to stock up on all the fish products you can find in the supermarket. Many species of fish — several of which end up on our plates — are displaying increasing levels of methylmercury, a very toxic substance. This is why it’s better to consult with your doctor before going all-in on a fish diet.

“Future laboratory studies may elucidate the underlying mechanisms, and clinical trials may demonstrate the effects of fish oil supplementation as one of the critical strategies for preventing PM_2.5-induced neurotoxicity. Since environmental pollution is unavoidable, these findings provide helpful insight regarding how healthy diet could reduce the adverse effects of air pollution on cognitive decline and neurodegeneration,” He concluded.

The findings were reported in the journal Neurology, published by the American Academy of Neurology.