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Explained: Can a diet of fish protect the brain from air pollution?

New study suggests that older women on a regular diet of baked or broiled fish (but not fried) may be consuming enough omega-3 fatty acids to counteract the effects of air pollution on the brain

Written by Mehr Gill , Edited by Explained Desk | New Delhi | Updated: July 19, 2020 11:34:12 am
fish, fish diet, benefits of fish, fish air pollution, health benefits of fish, fish effect on brain Food background, sliced portions large salmon fillet steaks on chopping board on dark blue concrete table, copy space, top view. (Source: Getty/Thinkstock)

New research has suggested that eating fish may help protect the brain from the effects of air pollution. The circumstances are specific, however: The study was conducted on a group of older women who ate more than one to two servings a week of baked or broiled fish or shellfish. Fried fish is not thought to bring the same benefits. The study is published in the journal Neurology, published by the American Academy of Neurology.

What is the connection between fish and air pollution?

Previous research had found that air pollution can affect the brain. Fish are known to be a source of omega 3 fatty acids. These fatty acids play an important role in the human diet and in human physiology, and have several health benefits.

The research investigated whether regular consumption of omega 3 fatty acids counteracts the effect of air pollution on the brain. Specifically, they measured omega 3 fatty acid levels and brain volumes of participants, and correlated these with their fish intake as well as PM2.5 levels in their home areas.

“Omega-3 fatty acids have been shown to fight inflammation and maintain brain structure in ageing brains. They have also been found to reduce brain damage caused by neurotoxins like lead and mercury. So we explored if omega-3 fatty acids have a protective effect against another neurotoxin, the fine particulate matter found in air pollution,” study author Ka He of Columbia University said in a statement released by the American Academy of Neurology.

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How was the study conducted?

It enrolled 1,315 women between ages 65 and 80 who were free from dementia at the start of the study, from 1996-1999. The researchers used the women’s addresses to determine their three-year average exposure to air pollution.

The women completed questionnaires about diet, physical activity, and medical history. From the diet questionnaire, researchers calculated the average amount of fish each woman consumed each week. This included broiled or baked fish, canned tuna, tuna salad, tuna casserole and non-fried shellfish, but fried fish was not included because deep frying is known to damage omega-3 fatty acids.

Participants were given blood tests. Researchers measured the amount of omega-3 fatty acids in their red blood cells.

The women underwent structural brain MRIs in 2005-2006 to determine the impact of PM2.5 on their brain volumes.

What were the findings of the new study?

Among women who lived in areas with high air pollution and had the lowest levels of omega-3 fatty acids, the researchers found more brain shrinkage than among those with higher levels of omega-3 fatty acids. In other words, women with higher levels of omega-3 fatty acids had greater volumes of white matter and hippocampus.

“Our findings suggest that higher levels of omega-3 fatty acids in the blood from fish consumption may preserve brain volume as women age and possibly protect against the potential toxic effects of air pollution,” said He.

What does it mean for the brain to shrink?

Ageing causes the brain to shrink in volume in humans and also tends to affect cognition. According to an article in the Postgraduate Medical Journal, as humans age, the chances of stroke, white matter lesions and dementia also rise, along with a level of memory impairment. Other factors such as stress may also cause certain areas of the brain to shrink in size.

A 2011 study published in PNAS said that while some age-related changes in the brain were observed in other species, a decrease in brain volume, particularly of the hippocampus and the frontal lobe, could be associated with humans alone. Researchers found that some areas of the brain shrunk by almost 25% by age 80.

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What are the limitations of the findings?

The researchers have cautioned that their study has only established an association between levels of omega-3 fatty acids and brain volumes. It does not directly prove that eating fish preserves brain volume.

Among other limitations, most participants were older white women, so the results cannot be generalised to others. Also, researchers were only able to examine exposures to later-life air pollution, not early or mid-life exposures. The researchers have suggested that future studies look at exposures to air pollution across a person’s lifespan.

Have the benefits of fish consumption for the brain not been studied previously?

A study published in March 2020 in the Frontiers of Aging Neuroscience said that fish intake may improve cognitive ability and affect the brain structure in healthy people.

In 2008, another study in Neurology reported that eating tuna and other types of fish may help in lowering cognitive decline and stroke in healthy older adults. This study found that people who ate broiled or baked fish high in omega-3 fatty acids three times or more per week had a nearly 26% lower risk of having silent brain lesions that can lead to stroke or dementia, compared to people who did not eat fish regularly.

How does PM2.5 impact the brain?

A 2019 study published in Ecotoxical and Environmental Safety reported PM2.5’s effects on the central nervous system which it can reach through a variety of pathways. For instance, PM2.5 can destroy the integrity of the blood-brain barrier and reach the central nervous system. Alternatively, PM2.5 could enter the brain through the olfactory nerve.

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