With that in mind, here's the latest turn: A Danish study finds that women who took fish oil supplements during pregnancy reduced the risk of asthma in their children.
"I would say that the finding that the effect was there was maybe not the surprise, because there have been indications," says the study's lead researcher, Dr. Hans Bisgaard, of the University of Copenhagen. "But the magnitude was very surprising to us."
Bisgaard is a pediatrician and runs a privately funded research enterprise called the Copenhagen Prospective Studies on Asthma in Childhood. He is not the first person to study whether fish oil supplements during pregnancy can affect asthma, but his study was large and carefully designed.
Researchers gave 2.4 grams of either fish oil capsules or olive oil capsules to more than 700 pregnant women during the third trimester of pregnancy. (Nobody knew which capsules contained the fish oil.)
They then monitored the health of the children for at least five years. And it turns out that 17 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 group that got olive oil. That's about a 30 percent reduction in cases of asthma or wheezing. (Because the Danish study included "persistent wheezing," it's not possible to compare these rates with asthma rates in the U.S.)
Bisgaard and his colleagues report their findings in Thursday's New England Journal of Medicine. He says by far the biggest benefit seemed to be among babies born to women who initially had low blood levels of the lipids found in fish oil.
That means, he suggests, a simple blood test during pregnancy could identify the women most likely to benefit from supplements. Bisgaard calls this strategy "precision prevention," because it targets women who are likely to see the biggest benefit and distinguishes them from "another population who may not need, really, to get this supplement."
Americans eat far less fish than Danes, so Bisgaard suspects a lot of the U.S. population would end up in the group who would benefit most 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.
"The confusion of the literature is overwhelming," Bisgaard says, "but the rationale for effect on inflammatory diseases is good."
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 help those infant airways develop in a way that makes them less susceptible to inflammation.
The study leaves many unanswered questions.
Maria Makrides, a research dietician at the University of Adelaide in Australia, says she would not recommend that women take fish oil supplements based on this study. Her own recent research, with a design similar to that of the Danish study, did not find that fish oil supplements reduced wheezing or other allergy symptoms.
Makrides has also published a review that highlights inconsistencies among published studies.
"It will be important to understand the differences we are seeing in some studies before we make strong general recommendations," Markrides told Shots in an email.
Dr. Ellen Mozurkewich, an OB-GYN at the University of New Mexico, agrees with that go-slow approach. She has also studied the relationship between fish oil and asthma and says she finds the Danish results "intriguing" but that she wouldn't recommend the supplements for her patients.
She says several studies show that women who take fish oil supplements during pregnancy tend to have larger babies.
"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," she says.
The babies in these fish-oil studies tend to gain an extra pound on average. The mothers "also did have more interventions for prolonged pregnancy," Mozurkewich points out, which, in turn, can lead to a more complicated delivery.
It would be great to run a really big study, at multiple universities, she says, to figure out whether fish oil really would prevent asthma in a diverse population.
Bisgaard agrees that his one careful exploration of the topic is not the final answer. "The problem," he laments, "is it's very, very difficult to get funding for these kinds of very patient studies."
You need a decade of steady funding, he says, and that's not going to come from a drug company. Preventing asthma many be important for public health, Bisgaard notes, but it's not appealing to a pharmaceutical company looking for its next lucrative product.
Fish oil during pregnancy reduces baby's asthma risk: study
(Reuters Health) - A Danish study of 695 pregnant women is raising the possibility that fish oil supplements begun in the final three months of pregnancy may reduce the risk of asthma or persistent wheezing in offspring.
The supplements brought the risk from 23.7 percent among mothers in the placebo group who took 2.4 grams of olive oil daily down to 16.9 percent in the women who got the fish oil capsules. That's a 30.7 percent reduction during the first three years of life.
The real benefit seemed to be exclusively among the children whose mothers started out with low levels of the two key ingredients in fish oil - eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). That may make them more vulnerable to the inflammation and heightened immune system response that is a factor in asthma and related conditions.
"If it weren't for the effects in that subgroup, then the results would have not been statistically significant," said Kathleen Melanson, a professor of nutrition sciences at the University of Rhode Island in Kingston, who was not involved in the research.
Among the Danish women with low EPA and DHA levels, the rate of asthma and wheezing in their children was 17.5 percent when the women took fish oil during pregnancy versus 34.1 percent when they took the placebo oil.
One in five young children are affected by asthma and wheezing disorders. In recent decades, the rate has more than doubled in Western countries. Previous research has shown that those conditions are more prevalent among babies whose mothers have low levels of fish oil in their bodies. The new large-scale test, reported in The New England Journal of Medicine, is the first to see if supplements can actually lower the risk.
Women can eat fish to get the same benefit but "you really need to be very fond of fish to get sufficient amounts through your diet" to have the effect seen in the study, chief author Dr. Hans Bisgaard of the University of Copenhagen told Reuters Health in an email.
The findings must be tested in other parts of the world, where fish oil consumption is lower.
That concern is echoed in an editorial in the journal by Dr. Christopher Ramsden of the National Institute on Aging, who said the 2.4 gram dose "was approximately 15 to 20 times as high as the average U.S. intake from foods."
"Before these findings can be applied to clinical practice, it is therefore imperative to ensure that this dose had no adverse effects on behavior, cognition, or other long-term outcomes," he said. "Future work is also needed to determine whether lower doses are effective and whether these results can be replicated in other populations."
Melanson told Reuters Health by phone that the dose used in the study was very high. The World Health Organization recommends no more than 3 grams per day, in part because excessive amounts can increase the risk of bleeding, lower blood pressure, and interact with medicines or vitamins A, D and E.
"Too much of a good thing is never a good thing," she said.
"It is possible that a lower dose would have sufficed," the Bisgaard team said.
Fish oil supplementation also lowered babies’ risk of lower respiratory tract infections, with the rate going from 39.1 percent with olive oil placebo to 31.7 percent with fish oil.
But the supplements didn't seem to affect the odds of a baby or toddler developing the skin condition eczema, or an allergy such as a reaction to milk or egg products, or a severe asthma attack.
The women began taking the fish oil and olive oil capsules at the 24th week of pregnancy and continued until one week after delivery.
The researchers calculated that 14.6 women would need to be treated to prevent one case of asthma or persistent wheeze. Among women with the lowest levels of EPA and DHA to start with, only 5.6 would need to be treated.
If the findings are confirmed in other populations, doctors could test to see who would mostly likely benefit from fish oil supplements. "The health care system is currently not geared for such," Bisgaard said. "But clearly this would be the future."
In the meantime, Melanson said, it would be premature to widely recommend fish oil during pregnancy.
Fish oil pills for pregnant moms may cut asthma risk in kids
Children whose moms took high doses of fish oil during their last three months of pregnancy were less likely to develop chronic wheezing problems or asthma by age 5, finds a study that suggests a possible way to help prevent this growing problem.
Asthma cases have been rising in developed countries, while consumption of omega-3 fatty acids like those found in fish has decreased. Some earlier studies suggested that omega-3 deficiency during pregnancy may affect asthma risk in babies, but they were too small to be definitive.
It's not known why this may be — one theory is that fish oil lowers inflammation, which can tighten airways.
Researchers at the University of Copenhagen in Denmark did a rigorous test, assigning about 700 women to take 2.4 grams a day of a supplement containing two types of fish oil, or look-alike pills of olive oil, in their third trimester of pregnancy, when babies' lungs are maturing. Neither the moms nor the researchers knew who was getting what until after three years, and then only the researchers knew until the children reached age 5.
Moms recorded how many episodes a child had of lung problems lasting for at least three days. This was called persistent wheezing until a child turned 3 and asthma after that.
Results: 17 percent of kids whose moms took fish oil developed a breathing problem by age 5 versus 24 percent of the comparison group — a reduction in risk of about one-third. There also were fewer cases of bronchitis, pneumonia and other such infections in the fish oil group.
However, almost all of the reduced risk occurred in children whose moms had the lowest blood levels of omega-3 at the start of the study. Fifteen women would need to take fish oil pills to prevent one case of wheezing or asthma if the whole group was taken into consideration, but only about five women would have to if just this lowest-level group was treated.
That suggests a possible way to tell who might benefit most if supplements are to be considered at all.
The results "are highly promising" but merit caution, Dr. Christopher Ramsden of the U.S. National Institutes of Health writes in an editorial in the New England Journal of Medicine, which published the study on Wednesday.
The fish oil dose in the study was 15 to 20 times as high as the average amount Americans get from food, and before it can be recommended, more study is needed to ensure that doesn't harm behavior, thinking abilities or other aspects of health, he writes. Doctors who wrote another article in the journal suggest that supplements are reasonable for women with a family history of asthma, especially since they are cheap and no major side effects were seen.
The study was paid for by the Lundbeck Foundation of Denmark and the Danish Ministry of Health and other groups. Some study leaders have a pending patent related to preventing asthma through gene and blood testing of moms.