ROBERT SIEGEL, HOST:
Studies of fish oil's impact on our health are like studies about coffee. There's plenty of contradictory information out there. And with that in mind, here is the latest turn. A Danish study finds that women who took fish oil supplements during pregnancy reduced their children's risk of developing asthma. NPR's Richard Harris reports.
RICHARD HARRIS, BYLINE: This is far from the first study looking at whether fish oil can help reduce the risk of asthma, but it is carefully designed. Hans Bisgaard at a privately funded research institute in Copenhagen spent the better part of a decade giving either fish oil or olive oil capsules to about 700 pregnant women and then following the health of their children.
HANS BISGAARD: I would say that the finding that the effect was there was maybe not the surprise because there have been indications. But the magnitude of the effect was very surprising to us.
HARRIS: Seventeen percent of the children in the fish oil group had developed persistent wheezing or asthma by the age of 5 compared with 24 percent of children in the olive oil group. That's 30 percent better. And Bisgaard says by far the biggest benefit was among babies born to women who started out with low levels of fish oil lipids in their blood.
BISGAARD: So what we are heading at at the moment is what we call precision prevention, where we can define the population of women who is likely to have a greater effect from supplement and another population who may not need really to get this supplement.
HARRIS: Americans eat far less fish than Danes, so he suspects a lot of the U.S. population could potentially benefit from fish oil during pregnancy. But this one study doesn't prove that it will be generally helpful, and other studies have come to conflicting conclusions.
BISGAARD: The confusion of the literature is overwhelming, but the rationale for effects on inflammatory diseases is good.
HARRIS: Inflammation is an important part of asthma. Small airways in the lungs can tighten up when they get inflamed, and laboratory studies suggest the lipids in fish oil may make those airways develop to be less susceptible to inflammation.
This report in The New England Journal of Medicine leaves many unanswered questions. Ellen Mozurkewich, an OB-GYN at the University of New Mexico, has studied fish oil. She says she wouldn't recommend it to her patients based on the results of this study, intriguing as it is. She says fish oil supplements given during pregnancy tend to result in larger babies.
ELLEN MOZURKEWICH: If you're prone to having a low-birth-weight kid, it might be good. And if you're prone to having a big kid, it might be bad.
HARRIS: The babies in fish oil studies tend to gain an extra pound on average.
MOZURKEWICH: They also did have more interventions for a prolonged pregnancy.
HARRIS: Which in turn can lead to a more complicated delivery. Mozurkewich says it would be great to run a really big study at multiple universities to figure out whether fish oil really would prevent asthma in the broad population. Bisgaard agrees that his one careful exploration of the topic is not the final answer. Both scientists spoke via Skype.
BISGAARD: The problem is it's very, very difficult to get funding for these kinds of very patient studies.
HARRIS: You need a decade of steady funding, and it's not going to come from a drug company. Preventing asthma is great for public health, but he notes it's not appealing to a pharmaceutical company looking for its next lucrative product. Richard Harris, NPR News.
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