December 29, 2016 — Women who took fish oil during the last three months of pregnancy significantly lowered the risk that their children would develop asthma, a study in Denmark has found.
Among children whose mothers took fish-oil capsules, 16.9 percent had asthma by age 3, compared with 23.7 percent whose mothers were given placebos. The difference, nearly 7 percentage points, translates to a risk reduction of about 31 percent.
But in the study released on Wednesday, the researchers say they are not ready to recommend that pregnant women routinely take fish oil. Although the study found no adverse effects in the mothers or babies, the doses were high, 2.4 grams per day — 15 to 20 times what most Americans consume from foods.
Before doctors can make any recommendations, the study should be replicated, and fish oil should be tested earlier in pregnancy and at different doses, Dr. Hans Bisgaard, the leading author of the study, said in an email. He is a professor of pediatrics at the University of Copenhagen and the head of research at the Copenhagen Prospective Studies on Asthma in Childhood, an independent research unit.
Doctors are eager to find ways to prevent asthma, a chronic disease that causes wheezing, coughing and breathing trouble, and that sends many families to the emergency room again and again.
The incidence has more than doubled in developed countries in recent decades. More than six million children in the United States have asthma, according to the Centers for Disease Control and Prevention, as do more than 330 million children and adults worldwide, according to the Global Asthma Network.
Dr. Bisgaard said it was not possible to tell from the study whether pregnant women could benefit from simply eating more fish. Pregnant women are generally advised to limit their consumption of certain types of fish like swordfish and tuna because they contain mercury. But many other types are considered safe, especially smaller fish like sardines that are not at the top of the food chain and therefore not likely to accumulate mercury and other contaminants from eating other fish.
The results were published in The New England Journal of Medicine. The scientists bought fish oil from a company that makes it, but they said the company had no role in the study. The research was paid for by the Danish government and private foundations.