Dirty air is the curse of urban living, and studies have shown that breathing it in harms the brains of men and women alike.
But a new study suggests that diet can help reverse the damage: Older women who regularly ate fish rich in omega-3 fatty acids seemed to better withstand the neurological effects of smog.
"Omega-3 fatty acids have been shown to fight inflammation and maintain brain structure in aging brains," explained study author Dr. Ka He, of Columbia University in New York City. "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."
To do so, He's team had more than 1,300 women, averaging 70 years of age, complete questionnaires about their diet, physical activity and medical history. None of the women had dementia at the beginning of the study.
Then, based on blood tests, the women were divided into four groups based on the amount of omega-3 fatty acids in their blood.
The women also underwent brain scans to assess the health of various areas of their brains, including white matter — which is composed of nerve fibers that send signals throughout the brain — and the hippocampus, which is associated with memory.
The women's home addresses were used to determine their three-year average exposure to air pollution.
Among women who lived in areas with high levels of air pollution, those with the lowest levels of omega-3 fatty acids in their blood had more brain shrinkage than women who had the highest levels of omega-3 fatty acids, the researchers reported July 15 in Neurology.
The findings suggest that eating more than one to two servings a week of baked or broiled fish or shellfish may provide enough omega-3 fatty acids to counteract the effects of air pollution on the brain, the researchers said.
"Fish are an excellent source of omega-3 fatty acids and easy to add to the diet," He said in a journal news release. "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."
The study was wasn't designed to prove cause and effect, He stressed.
"It's important to note that our study only found an association between brain volume and eating fish," He said. "It does not prove that eating fish preserves brain volume. And since separate studies have found some species of fish may contain environmental toxins, it's important to talk to a doctor about what types of fish to eat before adding more fish to your diet."
Katrina Hartog is a registered dietitian who manages clinical nutrition at Lenox Hill Hospital in New York City. Reading over the study, she said that while "the American Heart Association recommends eating fish twice per week to give you a heart-healthy amount of omega-3 fatty acids," the new study did have flaws.
Hartog said that there was some question as to the quality of the blood samples used in the study, data on foods containing omega-3s was incomplete, and "data on supplemental use of fish oil was collected, but frequency of use and dosage was not available."
The latter omission "is a major limitation, as many studies showcase this as a very effective way to increase omega-3 fatty acid intake," Hartog said.
She also noted that air pollution levels have declined in recent years, so it's tough to untangle whether improvements in brain health for some women was due to that trend or their fish consumption.
Nevertheless, eating more fish and omega-3s isn't a bad idea, Hartog said.
People "should consider including more omega-3 fatty acid foods into their diets and, better yet, substituting these foods for red and processed meats," Hartog said. The best sources of omega-3s are herring fish, mackerel, salmon, flaxseeds and chia seeds, she added.