Omega-3 fatty acids may reduce childhood asthma

More omega-3 fatty acids in the diet resulted in few asthma symptoms triggered by outdoor pollution, according to a new study by Johns Hopkins Medicine in Baltimore, Maryland, which was published today in the American Journal of Respiratory and Critical Care Medicine.

The six-month study included 135 children, ages 5 to 12 years old, from Baltimore City. Roughly a third each of the children had mild, moderate, or severe asthma, according to the study abstract.

The researchers defined asthma severity based on National Asthma Education and Prevention Program guidelines, which consider symptoms, inhaler use, and how well the lungs can forcefully breathe out. Generally, the more symptoms, the more medication use, and worse lung function, the more severe their asthma is considered. Diet, daily asthma symptoms, and daily inhaler use were reported by the participants and caregivers in surveys for one week each at enrollment, and again at three and six months. Researchers also collected blood samples to assess for changes in markers of inflammation.

During assessment weeks, researchers set up equipment in participants’ homes measuring two size ranges of air pollution, particles with diameters of 10 micrometers and smaller and particles with diameters of 2.5 micrometers and smaller. When inhaled, the larger particles typically deposit along the airways, whereas the smaller particles can penetrate farther into the lungs, reaching the tiny air sacs, researchers said. Both size ranges, though invisible to the naked eye, have been linked to asthma symptoms in children and adults.

The average concentration for the smaller particles in children's homes was 26.8 micrograms per cubic meter, while the annual Environmental Protection Agency standard for outdoor air is 12 micrograms per cubic meter. The average concentration for the range was 39 micrograms per cubic meter, the study said.

The study found that with each 0.1 gram increase in levels of omega-3 fatty acids in the diet reported on the survey, children had a 3 to 4 percent lower odds of daytime asthma symptoms in response to increases in both size ranges of air pollution by 10 micrograms per cubic meter, essentially, children who ate more omega-3 were less likely to have symptoms even at the same level of air pollution exposure.

Conversely, for each additional gram of omega-6 fatty acids, children had 29 percent higher odds of being in a more severe asthma category. Each additional gram of omega-6 in the diet was associated with a 2 percent increase in the odds of daytime symptoms in response to increased pollution levels of small particles by 10 micrograms per cubic meter. Essentially, children who ate more omega-6 fatty acids were more likely to have symptoms even at the same level of pollution exposure.

The results were similar for larger particle pollution, and for the outcomes of nighttime symptoms and inhaler use. More omega-6 fatty acids in the diet was also associated with higher percentages of a type of white blood cell linked with inflammation, neutrophils, in response to pollution.

The researchers said that the changes they used for omega-6 compared to omega-3 were 10 times higher. The investigators say this was intentional based on suggested dietary guidelines by the U.S. Department of Agriculture (USDA) for children. The USDA recommends consuming about of 0.9-1.6 grams of omega-3 fatty acids per day, which is equivalent to that in an approximately three ounce serving of salmon. The agency also suggests 10-16 grams of omega-6 fatty acids per day, which equivalent to that in around 3 grams or half a tablespoon of soybean oil, used in many fast food restaurants.

Children in the U.S., including those in Baltimore City, where they conducted the research, consume a diet that deviates sharply from national guidelines, researchers said. The diet consists of low amounts of omega-3-rich foods, and higher amounts of omega-6-rich foods, consistent with a typical American diet. The researchers recognize and acknowledge that many places where low-income people live are food deserts that lack access to healthy options, and that foods rich in omega-3 fatty acids may be more expensive. If diet proves to directly impact asthma health, eliminating these barriers will be a key step in reducing health inequalities and in combating asthma disparities in Baltimore City and elsewhere, the researchers said.  

The study used a questionnaire to assess diet, completed by children and caregivers, so the researchers acknowledge that errors in reporting are possible, one of the major limitations in dietary studies. However, the researchers used a questionnaire designed for residents of Baltimore City, with the hope of capturing relevant and common local foods and limiting this issue.

As this new study was observational rather than a randomized, controlled trial, the researchers said it doesn't prove cause and effect between fatty acids and asthma severity or symptoms. It's possible that other factors may have contributed to the relationship between fatty acids and asthma.