A third of all cases of childhood asthma under the age of five can be prevented if expectant mothers up their intake of omega-3 fatty acids, shows new research. (Photo: Shutterstock)

Taking fish oil while pregnant prevents childhood asthma

Children’s risk of developing asthma decreases significantly if the mother takes fish oil during the last trimester of pregnancy. The effect is especially strong among women who eat little fish and have a particular genetic variant.

Thomas Hoffmann

Published 5 January 2017 - 06:25

“It’s fantastic”

For Professor Hans Bisgaard from the University of Copenhagen, Denmark, research into the causes behind childhood asthma has reached a high point.

In a new study published in the New England Journal of Medicine, Bisgaard and colleagues report that the risk of developing asthma in childhood drops by as much as 30 per cent if expectant mothers take fish oil during their third trimester.

“It’s massive. If we can prevent one third of childhood asthma cases with fish oil then we’ve fundamentally changed the approach to a disease that we’ve tried to understand for many years,” says Bisgaard, professor of pediatrics and the head of the Copenhagen Studies on Asthma in Childhood research center (COPSAC) at the University of Copenhagen, Denmark.

Asthma is one of the biggest chronic childhood diseases, affecting around 235 million people worldwide.

Genetic variant boosts effect of fish oil

In the new study, Bisgaard and colleagues measured the level of omega-3 fatty acids in blood samples from pregnant women and compared this with their genetic profile.

The women who ate less fish and also have a special variant of the gene FADS--the GG variant, which makes it harder for the body to metabolise fish oil--stood to gain the most by taking fish oil.

Asthma prevention in this group was more than 50 per cent higher than the placebo group.

The findings of this five-year long study are a high point for Bisgaard.

“This is definitely a highpoint of my 35 years of research in childhood asthma. It doesn’t get bigger that this. I’m a happy man,” he says.

“The discovery is exciting, but we can also take the next step and designate the part of the population that will particularly benefit by taking fish oil, rather than just recommending it to everyone. It gives us the opportunity to make precision prevention,” says Bisgaard.

Well-designed study will be replicated in the USA

The new results agree with previous research by Susanne Hansen, a clinical epidemiologist form the Research Centre for Prevention and Health, Rigshospital, Denmark. Hansen published a paper earlier this year, where she reported that fish oil could protect against the development of asthma up to the age of 20.

The new study is well designed and carried out, says Hansen, who is especially impressed with the measurements of the women’s levels of polyunsaturated fatty acids.

“It’s interesting that the effect seems to be greatest among mothers with low levels of EPA and DHA at the start of the trial. It’ll be interesting to follow the children in the long term to see if the effect of fish oil can still be seen beyond the age of five,” she says.

Bisgaard now plans to replicate the study in the USA in collaboration with Harvard University. Americans consume around half the amount of fish as people do in Denmark, and even less than the women who participated in the Danish trial.

“If we can replicate the trial over there, then it will be up to the WHO or others to take the results out into the rest of the world,” says Bisgaard.

Asthma may be related to diabetes

Bente Klarlund Pedersen, head of the Tryg Foundation National Centre of Health at Rigshospital and a professor in the Department of Clinical Medicine at the University of Copenhagen, describes the new study as “solid, exciting, and extremely thorough” with big implications that may extend beyond asthma.

She suggests that the beneficial effects of taking fish oil may extend to other diseases.

“This is pure speculation, but maybe fish oil has an anti-inflammatory effect, which could be the reason that it lowers the risk of asthma. If so, then fish oil may have wider implications and also affect the risk of developing, for example, insulin resistance, which is associated with diabetes and high blood pressure,” says Pedersen.

“It would be exciting to reconvene the children in 15 years to see if the children who received fish oil also have less insulin resistance,” she says.

Further experiments will assess other benefits of fish oil

Bisgaard also suspects that this is the case.

In an earlier study he tracked the progress of 411 children whose mother’s were asthmatic. These children are now 18.

Part of the study involved exposing the children to ‘metabolic stress.’ They monitored how the children responded to a smoothie consisting of a mixture of fat, sugar, and protein.

They now plan to repeat this experiment on the children from the new fish oil study.

Initial results already suggest that boys’ IQ can be increased up to the same levels of girls, during their first year, and that pregnancy can be extended by a few days, which may prevent some premature births.

“We’ve reached something very fundamental, so I wouldn’t be surprised if you see a subsequent effect on the development of arthritis, bowel disorders, and the like, where both genetics and risk factors overlap with asthma,” says Bisgaard.

“I think the whole ancient Greek divisions of diseases into symptom-based diagnoses is misleading. For example, the generics of diabetes, obesity and asthma all overlap. I think that asthma could be the first of these inflammatory diseases, which provides a model of what might have an effect later in life,” he says.

Ten times recommended daily intake of fish oil

In the trial, 736 participants were given a dose of 400 milligrams of oil per day--ten times the typical daily intake--achieved by eating fatty fish twice a week. Half were given a placebo olive oil, and the other half were given fish oil.

It raises the question of whether pregnant women have the time or energy to remember to take a “horse pill’ of fish oil every day.

There are other drawbacks, says Bisgaard, including bad breath after consuming so much fish oil.

At this stage, the scientists do not know if such high doses are needed.

Hansen urges caution before pregnant women rush out to buy fish oil.

“Common sense is required,” she says.

“The best advice at present is to follow the health recommendations that pregnant women should eat 350 grams of fish per week--of which 200 grams should come from fatty fish. You may consider taking fish oil in pregnancy, especially if you don’t eat fish. But we need to consider all the evidence in the field before these recommendations are altered,” says Hansen.

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Read the Danish version of this story on Videnskab.dk

Translated by: Catherine Jex