Omega-3 fatty acids are one of the two major classes of polyunsaturated fat. They can be found in certain foods like flaxseed and fish, as well as in dietary supplements such as fish oil.

So far, research has indicated that omega-3 fatty acids - when consumed directly from food - have a variety of health benefits. A moderate consumption of seafood has been shown to reduce the risk of cardiovascular disease and has also been associated with a reduced risk of cognitive decline, Alzheimer's disease, and dementia.

A weekly consumption of at least 8 ounces of seafood by pregnant women also seems to improve health outcomes in their infants.

A new study - carried out by the Copenhagen Prospective Studies on Asthma in Childhood (COPSAC) research center in Denmark, in collaboration with the University of Waterloo, Canada - suggests an additional health benefit: reducing the risk of childhood asthma.

The Centers for Disease Control and Prevention (CDC) estimate that 6.3 million children in the United States under the age of 18 - or 8.6 percent of all U.S. children - currently have asthma.

As the CDC report notes, the prevalence of asthma has increased in the U.S. over the last decade, and the disease is currently at its highest level.

The authors of the new study hypothesized a link between the rising numbers of children affected by asthma in Western countries and the low levels of anti-inflammatory omega-3 in their diet. The researchers therefore examined the effect of omega-3 supplements in pregnant women on the risk of wheeze and asthma in their offspring.

Examining link between fish oil during pregnancy and childhood asthma

The researchers were led by Prof. Ken Stark, Canada Research Chair in Nutritional Lipidomics and professor in the Faculty of Applied Health Sciences at the University of Waterloo.

Prof. Stark and team selected 736 pregnant women who were 24 weeks into the gestation period. They randomly administered some of the women a daily dose of 2.4 grams of n-3 long-chain polyunsaturated fatty acids (LCPUFA) in the form of fish oil. The control group received a daily dose of olive oil as a placebo.

The LCPUFAs included eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These can be found in coldwater fish and are crucial for regulating the human body's immune response.

The researchers used rapid analytical techniques to measure EPA and DHA levels in the blood of pregnant women. Prof. Stark, who led the testing procedures, explains the benefits of using such a method.

    "Measuring the levels of omega-3 fatty acids in blood provides an accurate and precise assessment of nutrient status. Our labs are uniquely equipped to measure fatty acids quickly, extremely precisely, and in a cost-efficient manner."  Prof. Ken Stark

The mothers' offspring formed the 2010 COPSAC cohort, and they were followed for 5 years - the age at which asthma can be clinically diagnosed.

During the 5-year period, researchers monitored the children's health for asthma and persistent wheeze, as well as respiratory tract infections, asthma complications, eczema, and sensitization to allergens.

In total, the clinical trial included 695 children, 95.5 percent of whom completed a 3-year, double-blind follow-up period.

The results were published in the New England Journal of Medicine.
Omega-3 reduced childhood asthma risk by 31 percent

The results of the study seem to confirm the authors' hypothesis.

    "We've long suspected there was a link between the anti-inflammatory properties of long-chain omega-3 fats, the low intakes of omega-3 in Western diets and the rising rates of childhood asthma. This study proves that they are definitively and significantly related."
Prof. Hans Bisgaard, first author

The study revealed that pregnant women who took the daily dose of LCPUFA during the third trimester reduced their children's risk of developing asthma or persistent wheeze by almost 31 percent.

The treatment group had a 16.9 percent risk of persistent wheeze or asthma, compared with 23.7 percent in the control group. This corresponds to a relative risk decrease of 30.7 percent.

The blood tests also revealed that the supplements most benefited the women who had low levels of EPA and DHA at the beginning of the study. The supplements reduced the risk of asthma in their children by 54 percent.

The n-3 LCPUFA supplements were also associated with a decreased risk of lower respiratory tract infections, but they did not seem to have any effect on asthma exacerbation, eczema, or allergic sensitization.

The authors highlight the contribution of their study to asthma treatment and prevention options.

    "The proportion of women with low EPA and DHA in their blood is higher in Canada and the United States compared with Denmark. So we would expect an even greater reduction in risk among North American populations. Identifying these women and providing them with supplements should be considered a front-line defense to reduce and prevent childhood asthma." Prof. Ken Stark

"Asthma and wheezing disorders have more than doubled in Western countries in recent decades," adds Prof. Bisgaard. "We now have a preventative measure to help bring those numbers down."