LONDON The number of babies born in the US with neural tube defects has fallen by 19% since folic acid started to be added to bread and other grain products three years ago, according to new research (JAMA 2001, 285:2981-2986). The finding provides further ammunition for campaigners who feel that other governments have been dragging their heels over implementing a similar fortification policy.

On 13 January 2000 the Committee on Medical Aspects of Food and Nutrition (COMA), a group of independent scientific experts, recommended that folic acid should be added to flour in order to reduce the incidence of neural tube defects in the UK. There then followed a consultation period, which ended last October. Nothing more has happened since then.

Nick Wald, a member of the COMA advisory committee and Professor of Environmental and Preventative Medicine at the Wolfson Institute of Preventive Medicine in London, said: "I don't know why there has been such a delay. It is not an area where there seems to be any great scientific or public disagreement."

A spokesman for the UK Department of Health explained: "We are still waiting a final decision from the health minister. The results of the consultation process suggested that there were a number of benefits of fortification but there are a number of other issues to be considered, for example the possible effect on older people."

Folic acid is an artificial form of the natural B vitamin folate, found in foods such as broccoli and Brussels sprouts. It has the same vitamin function and activity as natural folate but is better absorbed. Folate is thought to be involved in the production of methyl groups, which in turn are involved in DNA replication. A deficiency in folate leads to impaired cell replication. One of the first parts of the foetus to develop is the central nervous system. The crucial time is the first 25 days of pregnancy when the neural tube, from which the spinal cord and brain develop, is formed. Spina bifida is caused by the failure of the neural tube to develop properly. Related defects are anencephaly (the absence of a brain) and encephalocele (a malformation of the brain and skull). Increasing folic acid intakes could prevent around two thirds of neural tube defect-affected pregnancies.

The first conclusive evidence supporting folic acid supplementation came from the large Medical Research Study Vitamin Study, which started in 1983. It found that women who have had a pregnancy affected by a neural tube defect can reduce the chances of having a second affected pregnancy by 72% if they take 4 mg folic acid a day (Lancet 1991, 338:131-137). Further studies supported the hypothesis that there would be a similar protective effect in low risk pregnancies (NEJM 1992, 327:1832-1835).

In March 1996, the US Food and Drug Administration authorised the addition of folic acid to grain products such as breads, pasta, rice, flour and cereals. And in January 1998 they made such an addition mandatory.

The latest research carried out by the National Center on Birth Defects and Developmental Disabilities in Atlanta showed that the prevalence of neural tube defects decreased from 37.8 per 100,000 live births before fortification to 30.5 per 100,000 live births after mandatory folic acid fortification, representing a 19% reduction. But, the figures may be imprecise because the researchers used birth certificate data, which do not include foetal deaths or babies who are stillborn, and many birth defects go unrecorded on certificates. In addition, many foetuses with neural tube defects are identified during pregnancy leading to a termination.

The current UK government recommendation is for women to take a supplement of 400 micrograms of folic acid a day from before conception until the end of the first 12 weeks of pregnancy. But, a MORI survey carried out last year for the charity Action Research found that only 15% of women questioned took folic acid before pregnancy. This is supported by research that found no decline in neural tube defects since the Health Education Authority launched an awareness campaign in 1996 (Lancet 1999, 354:998).

Tony Britton, publicity manager at the Association for Spina Bifida and Hydrocephalus, a UK charity, said: "The current strategy is ineffective as around 50% of pregnancies are unplanned. By the time pregnancy is confirmed, which is often around two months, it is too late as any damage will have been done."

There is some debate over the optimal level of fortification. The US adds 140 micrograms of folic acid per 100g of grain. The COMA report called for universal fortification of flour at a higher level — 240 micrograms per 100g. It said this would reduce the incidence of NTD-affected pregnancies by 41% without resulting in unacceptably high intakes in any group of the population.

Wald said: " I think the 240 microgram level is still probably too conservative. But if we start at this relatively modest amount we can review it upwards later." Even if fortification were introduced, not all women would achieve the desirable levels of folate intake of 600 micrograms a day. So he advised that women trying to conceive a baby should still take folic acid supplements. "Fortification will just be a partial safety net."

The main objection to universal fortification is that raised intakes of folic acid could mask vitamin B₁₂ deficiency, particularly in older people. This is because folic acid can delay or prevent anaemia due to vitamin B₁₂ deficiency but not the nerve damage that could go undetected. But, Wald rejected this argument. "It just means the presentation of the disease is slightly different. If you suspect vitamin B₁₂ deficiency, instead of looking for anaemia you need to carry out a B₁₂ assay."

It is not just pregnant women who might benefit from raising levels of folic acid. There is some evidence that increasing dietary folate reduces the risk of cardiovascular disease. It is known that people with raised blood levels of the amino acid homocysteine are at greater risk of cardiovascular disease. It has also been shown that increasing folate intake reduces homocysteine levels in the blood. But it has not yet been proven conclusively that increasing folate intakes and thereby lowering homocysteine levels, will reduce the risk of cardiovascular disease in the general population. COMA concluded that the evidence is not, as yet, conclusive. But, Wald considered that the evidence was compelling.

There are hopes that the UK will now move to implement a food fortification policy. Britton said: "Now the election is over we hope the Department of Health will dust off the COMA report and reconsider it." At a global level, the World Health Organization recommends measures should be adopted in all countries to ensure adequate folate intake by adolescent girls and women of childbearing age prior to conception in populations at increased risk of neural tube defects.