The Food Standards Agency will recommend this week that the vitamin be added to all loaves and flour, The Times has learnt. It will be the first time since the Second World War that food manufacturers have been ordered to add nutrients to improve the nation’s health.

Experts believe that the compulsory addition of folic acid will reduce the number of cases of spina bifida and other defects by 40 per cent. The vitamin also reduces miscarriages and may help to combat strokes, heart disease and bone disorders in adults.

The decision will raise concerns from some consumers at the erosion of personal freedoms. Compulsory addition of folic acid was ruled out by the agency four years ago because medical experts feared that it would mask a vitamin deficiency in the elderly.

However, adding folic acid will lessen the 200 cases of babies born each year with spina bifida or other neural tube defects. It will also relieve the distress of up to 750 women a year who have an abortion after discovering that their baby may be born with neural tube defects.

In the US, Canada and Chile, the compulsory addition of folic acid in food has reduced neural tube defect pregnancies by as much as 50 per cent.

The agency’s advisory committee estimates that if flour were fortified with folic acid at levels of between 100 and 450 micrograms per 100 grams, the number of pregnancies affected by neural tube defects would fall by between 40 and 370 a year. The committee said it now favours compulsory addition of folic acid provided that GPs can monitor the scale of B12 deficiency in elderly patients. Lack of it can trigger anaemia and damage to the nervous system.

“The potential health benefit of the mandatory fortification of flour with folic acid is substantial: whereas the available evidence suggests the potential risks are uncertain,” it said.

The agency will hold a public consultation over the summer and plans to give the go-ahead for folic acid in flour in September. It will decide if the order will apply to all flour or just that used in breadmaking. Health ministers will then approve a change in the law. There may be exemptions for some wholemeal and stoneground flour.

Women thinking of becoming pregnant are already advised to take folic acid supplements and to eat foods such as broccoli, Brussel sprouts, beans and peas, which are rich in the vitamin. But half of all pregnancies are unplanned, and the women most at risk are those from poor income groups who are less likely to take vitamins out of ignorance or forgetfulness.

The National Association of Millers in Ireland and Britain and the Federation of Bakers said they were willing to add folic acid to flour. Sue Davies, the chief policy adviser at Which?, which previously expressed reservations about folic acid in flour, said: “The evidence indicates that there would be clear benefits from fortification of flour.”

Times Recommends

• Madonna and her Guy decide it’s over
• Terror police target internet phone calls
• Red squirrels develop immunity to grey plague