The last scientific objection to adding folic acid to flour has been swept away by researchers who insist ministers must now act to save hundreds of babies a year.
An upper daily limit for consumption of the vitamin should be abandoned because it was based on a “ridiculously elementary” mistake in a 20-year-old study, the scientists say.
No evidence now remains that high levels of folic acid are dangerous and ministers will be culpable if they do not implement expert advice to add it to white bread flour to prevent birth defects, they argue. More than 800 babies a year develop neural tube defects such as spina bifida because their mothers get too little folic acid, and four in five are aborted when this is discovered.
Most people do not get enough in their diet and women trying to conceive are advised to take supplements.
By the time women know they are pregnant, however, it is often too late for the vitamin to help the developing brain and fewer than one in three are taking supplements at the crucial stage.
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The official scientific advisory committee on nutrition has long recommended that folic acid be added to bread flour and doctors have written to The Times to back mandatory fortification.
Currently, people are advised to take no more than a milligram of folic acid a day, about two and a half times the level in pregnancy supplements. Concerns about cancer have been dispelled by studies and researchers have traced the source of the 1mg limit to a 1998 US paper on the risk of nerve damage.
Yet this paper did not calculate percentages properly and re-analysis shows no higher level of damage in people taking very high levels of folic acid, according to results to be published today in Public Health Reviews.
“With the upper limit removed there is no scientific or medical reason for delaying the introduction of mandatory folic acid fortification in the UK,” said Sir Nicholas Wald, a professor at Queen Mary University of London.
“Every day in the UK, on average two women have a termination of pregnancy because of a neural tube defect and every week two women give birth to an affected child. It does seem a tragedy that could be so easily and safely prevented.”
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The US and 80 other countries fortify flour since Sir Nicholas’s original 1991 study. He said ministers had “no excuse for delay.”
A quarter of defects could be prevented with low-level fortification, rising to 70 per cent with a high dose.
David Smith of the University of Oxford said a lack of harm had not been proved, however.
“The introduction of fortification would expose between 580,000 and 844,000 people in the UK to extra folic acid for each neural tube defect pregnancy prevented. Can we be sure that in this large proportion of the population no one would suffer harm from the folic acid? The answer must be ‘No’,” Professor Smith said.
The Department of Health and Social Care said it was considering the recommendations.