Bread should be fortified with folic acid by law to cut the risk of birth defects, the Food Standards Agency decided yesterday.

The FSA board, which was split on the issue when it was last discussed in 2002, decided unanimously to back a recommendation from its scientific advisers for mandatory fortification of flour or bread, whichever is the more practicable.

In the US, Canada and several other countries, mandatory fortification has already cut sharply birth defects such as spina bifida. But Britain has hung back because of doubts about possible side-effects, and fear that “compulsory medication” would cause a public outcry.

The recommendation will now go to ministers, who will decide whether to implement it. If they do they could face opposition in the House of Commons but will be able to cite a mass of evidence gathered by the FSA.

The mandatory fortification of bread would include regular white and brown bread, but not wholemeal, enabling objectors to opt out. It would also be accompanied by controls on food that are already fortified voluntarily by manufacturers, such as some breakfast cereals, to avoid any possibility of an overdose.

The FSA board was given a range of options to consider, including the present policy of advising women planning pregnancies to take folic acid supplements. But half of pregnancies are unplanned, and the advice does not reach women in lower social classes whose diets are the most likely to be deficient. It has had relatively little effect.

The levels of fortification recommended by the FSA are 300 micrograms per 100 grams of flour, which it estimates will increase the average intake of the UK population by 78 micrograms a day.

That should cut the incidence of neural tube defects by between 11 and 18 per cent, or between 77 and 162 cases a year. Greater reductions than this have been achieved abroad, and range from 27 to 50 per cent.

But direct comparisons are difficult because they depend on the level of folic acid in the diet of each country before fortification began, and on eating patterns. The US achieved much greater increases in folic acid intake, probably because the amounts added to food exceeded the recommendations.

Dame Deirdre Hutton, chair of the FSA, told the board meeting in Nottingham that she supported the measure. “I don’t believe it is the ultimate solution. I believe it is the best pragmatic solution we can get,” she said.

The FSA board wants further advice on how folic acid can be added to bread without affecting cakes or biscuits. It called for more debate on how products fortified with folic acid should be labelled. Andrew Russell, the chief executive of the Association for Spina Bifida and Hydrocephalus, said: “We are delighted that the FSA board has taken the decision to recommend mandatory flour fortification to ministers.

“It is a rare opportunity to benefit from a vitamin, and significantly improve public health. Now that the science has been listened to, we look to health ministers to speedily implement this life-saving measure.” Between 700 and 900 pregnancies per year in the UK are affected by neural tube defects (NTDs) such as spina bifida. The majority are terminated when the defects are detected in antenatal checks.

The FSA estimated that the cost of NTDs was £136 million a year, of which the greatest cost was in treating babies who died soon after birth. Of the 800 affected pregnancies each year, 110 end in stillbirths or deaths early in life; 79 in births of children who require treatment but have good life expectancy, and 611 in terminations.

The FSA’s decision is in stark contrast to that of 2002, when the measure was rejected. The fear then was that fortifying flour with folic acid would conceal vitamin B12 deficiencies in older people, leading them to medical problems.

The unknown effect of excessive folic acid consumption on cancer risk also caused concern. Since then, the US has found no evidence of harm.

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