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 per cent had asthma by age three, compared with 23.7 per cent whose mothers were given placebos.

The difference, nearly 7 per- centage points, translates to a risk reduction of about 31 per cent.

But in the study released last 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 - 2.4g 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, said Dr Hans Bisgaard, the leading author of the study.

He is a professor of paediatrics at the University of Copenhagen and the head of research at the Copenhagen Prospective Studies on Asthma in Childhood, an independent research unit.

More than six million children in the United States have asthma, according to the Centres for Disease Control and Prevention, as do more than 330 million children and adults worldwide, according to the Global Asthma Network.

The results were published in The New England Journal Of Medicine. The Danish government and private foundations paid for the research.

A total of 736 women were recruited for the study.

About a quarter of the mothers and a fifth of the fathers had asthma, and they were evenly distributed between the fish-oil and placebo groups.

The capsules were an over-the- counter product called Incromega TG33/22, a fish extract made by a British chemical company. The extract contained the fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

The researchers tracked the children's health, finding asthma less common in those whose mothers had taken the fish oil, with the effect lasting at least through age seven.

By age three, the biggest difference had emerged from data on mothers who, before treatment, had the lowest levels of EPA and DHA in their blood.

In that group, only 17.5 per cent of the children whose mothers took fish oil developed asthma, compared with the 34.1 per cent whose mothers took the placebo - a difference of 16.6 percentage points and a risk reduction of about 54 per cent.

THE NEW YORK TIMES