The risk of developing asthma has been reduced by 63% in children whose mothers were given fish oil supplements during the last trimester of their pregnancy as part of a European research project on nutrition.

The research is part of a broader project on early nutritional programming which involves experts from 16 countries and is financed by the European Commission’s research programme.

The Danish researchers originally carried out a trial with 500 pregnant women in the last 10 weeks of their pregnancy in 1990 to examine the effect of fish oils on pre-term birth and low birth weight. One group was given fish oil supplements, another olive oil supplements and the third no supplements.

When the babies born in that trial were later traced, it was found that by the age of 16, 19 children had developed such severe asthma at some point that they had had to go to hospital. However, fewer of these children were in the fish oil group than the other two. The risk of developing asthma was reduced by 63% in those whose mothers had been given fish oil supplements.

There is strong biochemical evidence that the omega-3 fatty acids in fish oil may have effects on the immune system. The reason fish oil might protect a foetus from developing asthma in later life could possibly also be related to its effect on increasing pregnancy duration.

Pre-term children have a higher risk of developing asthma and it is possible that the omega 3 fatty acids found in fish oils could both reduce the risk of pre-term birth and the likelihood of a baby later becoming asthmatic. It may be that the period shortly before delivery is the critical window for these effects of omega 3 fatty acids. However, further trials are necessary before dietary recommendations for pregnant women should be changed.

The research is published today in the American Journal of Clinical Nutrition.