Adding folic acid to food might cut the number of strokes, according to an analysis published today.

In the US and Canada, where folic acid fortification of flour began almost ten years ago, there has been a sharp decline in strokes. Strokes were falling at the rate of 0.3 per cent a year in the US between 1990 and 1997, but the decline accelerated to 2.9 per cent a year after 1998, when fortification began.

In Canada, the effect was even greater – a 5.4 per cent annual decline in strokes after fortification, against 1 per cent a year before. Strokes have been declining in the UK too, but there has been no similar acceleration since 1998.

However, it does not demonstrate cause and effect, and randomised controlled trials of folic acid have produced mixed results. To try to identify any real effect, a team from the US and China, led by Xiaobin Wang, of Northwestern University in Chicago, pooled the results of eight trials. These involved giving people folic acid supplements over periods varying from two to six years and comparing their outcomes with those of matched controls given placebo pills.

Six out of the eight trials showed a reduction in strokes, sometimes by big amounts, while two showed an increase. When pooled, Professor Wang and researchers say in The Lancet, the net result was that folic acid supplementation reduced strokes by 18 per cent.

How this was achieved, the team believes, was by the reduction of homocysteine, a chemical in the bloodstream, high levels of which are linked to higher levels of heart attack and stroke; it has been shown that folic acid reduces it.

The finding adds weight to the recent proposal from the Food Standards Agency that folic acid should be added to bread, or flour, in Britain. But the potential impact on strokes might be even more beneficial, if Professor Wang and her team are right. In making the proposal, the Food Standards Agency relied on advice from its scientific advisory committee, which concluded that the evidence of cardiovascular benefits of folic acid was unproven.

Many experts remain sceptical about the stroke benefits.

Peter Coleman, deputy director of research at the Stroke Association, said: “The findings are inconclusive. Supplementing the diet with folic acid may reduce the risk of stroke in certain individuals, but is not suitable for everybody, and could increase the risk of cardiovascular disease in some people.

“We urge people to consult with their doctors before taking any supplements or medication with a view to reducing their risk of stroke.”

Adding folic acid to flour would probably not have as great an effect as Professor Wang estimates, because the proposed fortification level is lower than that achieved in the trials using supplement pills.

Every year, 130,000 people in Britain have a stroke. It is the third commonest cause of death and the commonest cause of disability. An 18 per cent reduction would amount to 23,000 strokes a year.

Cynthia Carlsson, of the University of Wisconsin, said in The Lancet that Professor Wang’s analysis had helped to clarify the issue but more trials were needed.

Pluses and minuses

Advantages

— Adding folic acid to flour or bread would cut the number of babies born with neural tube defects such as spina bifida by between 77 and 162 every year and obviate hundreds of terminations

— It would be more effective than simply advising women to take folic acid supplements, which has not worked. Half of all pregnancies are unplanned

— It might help to reduce strokes, as it seems to have done in the US.

— But the science is uncertain, so this alone would not justify the measure

Disadvantages

— For older people, there is a risk that fortification of food might conceal vitamin B12 deficiencies and prevent their detection. But there is no evidence that this has happened in the US or Canada

— Voluntary fortification of foods such as breakfast cereals would have to stop

— Ministers would have to take a decision that might make them unpopular

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