Women taking folic acid supplements throughout pregnancy may increase the risk of asthma in their child by 26 per cent, research has suggested.

The researchers from the Univerity of Adelaide in Australia said the findings may help explain why there has been an increase in allergic asthma in children over the last 20 years.

In the study almost 500 mothers were questioned about their folic acid supplementation, diet and lifestyle habits like smoking. They found that women who took folic acid supplements in late pregnancy were 26 per cent more likely to have children diagnosed with asthma by the time they reached three and a half years old.

The research did not find any link between childhood asthma and folic acid intake before pregnancy or during the first trimester.

The findings were published in the American Journal of Epidemiology.

There are around five million people in Britain with asthma, including more than one million children.

It is thought folic acid may interfere with proteins connected to the body's immune system making it more sensitive to allergens and so increasing the likelihood of asthma, the researchers wrote.

Prof Michael Davies, corresponding author of the paper, said: "In the first study to show a link between folic acid supplements and asthma in children We believe that this is the first published study in humans to demonstrate that increasing consumption of folic acid, and specifically supplemental folate during late pregnancy significantly increases the risk of physician-diagnosed asthma in the chilren at 3.5 years."

Current guidelines say women planning a pregnancy and those in their first trimester should take folic acid supplements.

Prof Davies added: "Our findings are in agreement with current recommendations pre- and in early pregnancy. However, they highlight the need to consider current supplementation strategies so as to maximise the neuroprotective effects of folic acid while minimising potential adverse postnatal respiratory effects.

"We acknowledge the need for further studies replicating our findings before any specific recommendations against folic acid supplementation in late pregnancy can be made."

It comes after the Food Standards Agency recommended that folic acid be added to be bread in the UK even though there has been suggestions this may increase cases of bowel cancer in the general population.

Leanne Metcalf, Director of Research at Asthma UK, said: "As the relationship between folic acid and asthma has only recently come under scrutiny, it is important to emphasise that further research is needed before we can make any definite recommendations.

"At the moment however we can say that the benefits of taking folic acid supplements in pregnancy, particularly with regards to prevention of birth defects like spina bifida, far outweigh the risk of developing asthma so we would advise expectant mothers to continue taking dietary supplements as directed by their doctor.

"We know that eating healthily is vital during pregnancy so we would strongly urge all mums-to-be to eat a healthy balanced diet and not to smoke during pregnancy to give their baby the best possible chance of a healthy, asthma-free childhood."

Source: Telegraph.co.uk, 5th Novemeber 2009

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