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It has long been known that air pollution affects the risk and severity of asthma. Now there is evidence that diet can also play a role.
A recent study shows that higher levels of omega-3 fatty acids in oily fish such as salmon, sardines and trout, and some plant sources than walnuts and flaxseed, are associated with reduced asthma symptoms in urban children high indoor air pollution.
"We know that asthma is a problem caused by inflammation," explains Dr. Emily Brigham, pulmonologist at Johns Hopkins University and co-author of the study. When our body digests fish, the omega-3 fatty acids produce byproduct molecules called "pro-resolution mediators" that enter the lungs. "They help eliminate inflammation," says Brigham.
Given this anti-inflammatory effect, Brigham and her colleagues hypothesized that diets rich in omega-3 fatty acids may mitigate the effects of air pollution on children's symptoms. To study this, they tracked indoor nutrition and air pollution (from sources such as smoke, dust and allergens) in the homes of 135 children, mostly of African-American descent and all with asthma, in Baltimore, Md.
. They measured two types of indoor air pollution, consisting of different particle sizes: PM2.5 (fine respirable particles that are 2.5 microns or smaller) and the slightly larger PM10. These particles are too small for us, but they can get into our airways, and the smaller size – PM2.5 – can get stuck deep in our lungs.
"What we found was the reported intake of omega-3 has been associated with reduced effects of indoor particles on the symptoms," says Brigham. "Children who consumed more omega-3 fatty acids appeared to be more resistant to the effects of PMs."
Brigham and her team also investigated the intake of omega-6 fatty acids that are found in vegetable oils and are present in many processed foods that contain oil. Normally Americans eat a lot more omega-6 acids compared to omega-3 fatty acids. This also applies to all children in the Baltimore study. The study found that children who consumed the most omega-6 fatty acids had more severe asthma symptoms.
Brigham says the role of omega-6 fatty acids in inflammation is complicated. It has been shown that some by-products of omega-6 acids, such as leukotrienes, are proinflammatory. "Leukotrienes are one of the molecules known to cause inflammation in asthma," she says.
Now that this is an observational study, researchers can not prove that the omega-3 acids cause a decrease in symptoms, or that the high intake of omega-6 acids causes more severe symptoms. However, the results are consistent with a variety of evidence documenting the anti-inflammatory effects of omega-3 fatty acids.
And when it comes to mitigating the effects of air pollution, there are other studies that support the assumption that dietary interventions can help provide protection.
"This study complements a growing body of literature suggesting that nutrition – Western, Mediterranean, etc. – can affect the health effects of air pollution," says Kym Gowdy, Professor of Pharmacology and Toxicology at East Carolina University ,
It refers to a recent study published in the journal Circulation which found that a Mediterranean-style diet reduces the risk of death from cardiovascular disease due to long-term exposure to air pollutants
] "The [new] study by Dr. Brigham supports the general view that nutritional status is an important factor that should be taken into account to improve protection against air pollution," says Neil Alexis, a professor at UNC Chapel Hill School of Medicine, North Carolina, USA
And although Brigham's study focused on the helpful fatty acids in foods, Alexis notes that another study has found that even antioxidant supplements can help reduce the effects of ozone pollution on the small-respiratory tract of children with moderate to severe asthma. In a separate study from 2018, it was found that vitamin E helped reduce the inflammatory features of asthma.
In general, a diet that is high in fruits, vegetables, nuts, seeds and healthy fats – including omega-3 fatty acids – has many documented health benefits. including a reduced risk of cardiovascular disease. The new study indicates another potential benefit, especially for people exposed to air pollution. And when it comes to getting enough omega-3s: US dietary guidelines recommend that adults consume 8 ounces of seafood a week, and small children a little less.