Mar 232017

Can fish oil supplements taken during pregnancy prevent asthma in children? According to a randomized trial in the New England Journal of Medicine, yes.

Children of 736 pregnant women who took supplements containing given n-3 long-chain polyunsaturated fatty acid during their third trimester had a 31% relative reduction in risk of developing asthma or persistent wheezing as young children, as compared with kids whose mothers took olive oil (17% versus 24%, HR 0.69, 95% CI 0.49-0.97, P=0.035), according to Hans Bisgaard, MD, head of the Pediatric Asthma Center of the University of Copenhagen in Denmark, and colleagues.

Fish oil's apparent benefits were even more pronounced among kids whose mothers had the lowest natural levels of omega-3 fatty acids in their blood. These children had a 54% relative reduction in the incidence of asthma or persistent wheezing (18% vs. 34%). Many of these mothers had genetic variants that reduced their ability to produce omega-3s from dietary alpha-linolenic acid. An editorialist wrote:

Together, these observations support the plausibility of the findings and point towards a precision-medicine approach in which factors such as blood levels of fatty acids, genotype, and parental history of asthma could potentially be used to tailor interventions to those most likely to benefit ... These results also highlight the importance of measuring baseline EPA and DHA levels in future trials involving fish oil.

The trial was done in Denmark. The dose of fish oil was 2.4 grams per day. The actual product was called Incromega TG33/22, a fish extract manufactured by the British chemical company Croda Health Care. The product contains the fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA).

Children were followed for a total of 5 years. About 700 children were included, and about 20% were diagnosed with asthma or persistent wheezing by age 5.

Fish oil showed a remarkable and cost-effective benefit in this trial, preventing one child from developing asthma/wheezing by treating only 15 women. Treating only 6 women with the lowest omega-3 levels would prevent a child from developing asthma/wheezing -- if the results were to hold true in larger populations.

Children whose mothers took fish oil also had about a 23% relative reduction in respiratory infections. There were no obvious adverse events.

The children's young age at the end of trial follow-up precludes definite conclusions about fish oil's power to permanently banish asthma from a developing person's life. Longer-term followup -- more feasible in Denmark's single payer system than in the U.S. -- may help answer this question.

Read more:

Fish Oil–Derived Fatty Acids in Pregnancy and Wheeze and Asthma in Offspring. N Engl J Med 2016; 375:2530-2539.

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Fish oil in pregnancy prevented asthma in kids at age 5