Folate and prevention of neural tube defectsBMJ 2014; 349 doi: http://dx.doi.org/10.1136/bmj.g4810 (Published 29 July 2014) Cite this as: BMJ 2014;349:g4810
- Robert Clarke, reader in epidemiology and public health medicine,
- Derrick Bennett, senior statistician
- 1Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, University of Oxford, Oxford OX3 7LF, UK
- Correspondence to: R Clarke
Neural tube defects are the most common disabling birth defect and can be reduced by 80% if women of childbearing age consume 400 µg of folic acid daily.1 In the United Kingdom, where roughly 800 pregnancies are affected each year, the Scientific Advisory Committee on Nutrition recommends that all women planning pregnancy should take 400 μg folic acid daily as a supplement before conception and until the 12th week of pregnancy (or 5 mg daily for women with a previous pregnancy affected by a neural tube defect).1 As half of all pregnancies are unplanned and less than a third of all women start taking folic acid before becoming pregnant,2 voluntary folic acid fortification has been permitted in the United Kingdom (and elsewhere in most European countries), and mandatory fortification has been implemented in North America, South America, and Australia 1. The relative efficacy and safety of voluntary and mandatory folic acid fortification programmes are uncertain.
The study reported by Crider and colleagues in The BMJ (doi:10.1136/bmj.g4554) was designed to determine the optimal red blood cell (RBC) folate concentrations required to prevent neural tube defects.3 The authors analysed data from two studies in non-fortified populations from two regions in China: a community intervention study testing folic acid supplementation to prevent neural tube defects that included 275 cases in 247 831 women treated with folic acid 400 µg daily;4 and a population based randomised trial to evaluate the effects of folic acid supplementation in a subset of 371 women of reproductive age who provided RBC folate concentrations after treatment with 400 µg daily.5
The results show an inverse dose-response association of neural tube defect risks with RBC folate concentrations—participants with the lowest red cell folate concentrations had the highest risk of neural tube defects (25.4 v 6/10 000 for 500 v 1200 nmol/L).3 The authors defined the threshold for optimal RBC folate concentrations for prevention of neural tube defects as 1000 nmol/L. These results are concordant with the results of a previous study by Daly and colleagues in Ireland. Their study, which included 84 cases, reported a threshold of 906 nmol/L, above which the risk of neural tube defects was minimal.6
Applying the risk model developed from the Chinese data to population RBC folate concentrations in the United States, before and after fortification, Crider and colleagues showed that their predicted estimates for the prevalence of neural tube defects were concordant with the observed prevalence before and after fortification, confirming the validity of their model. Taken together, the Chinese, Irish, and US data indicate that RBC folate concentrations of about 1000 nmol/L or greater should be the population target for preventing neural tube defects. These findings are important and provide a clear target for RBC folate concentrations that should help guide the choice of population fortification strategies.
Traditionally, RBC folate concentrations have been viewed as a better measure of folate status than serum folate concentrations, as they reflect folate status throughout the cell’s 90-120 day lifespan. However, red cell folate is unlikely to be a useful biomarker for individual women in the foreseeable future. Red cell assays are available only in specialist laboratories, whereas serum folate assays are readily available in most clinical laboratories, at least in developed countries, where they are widely used for measuring folate status in individual women.
Both tests can be useful for monitoring a population’s response to changes in folate policies, and both should be included in nationally representative surveys of folate status such as the National Health and Nutrition Examination Survey in the United States.7 Data from this survey, reported by Crider and colleagues, suggest that with mandatory fortification, three quarters of the US population have adequate serum concentrations of folate and optimal RBC folate concentrations for preventing neural tube defects.3 Data from Ireland, which operates a voluntary policy, paint a less healthy picture—median serum and RBC folate concentrations in one recent survey were about 17 nmol/L and 700 nmol/L, respectively, in non-supplement users and 30 nmol/L and 1000 nmol/L in supplement users.8 Mandatory fortification in the United States (average daily dose of folic acid 0.14 mg) is associated with substantially greater population folate concentrations, which translates in to a substantially lower risk of neural tube defects.9
Moreover, voluntary folic acid fortification causes more extreme variation in folate status within populations (with low intakes in lower socioeconomic and ethnic minority groups and high intakes in users of high dose supplements).1 Consequently, the Scientific Advisory Committee on Nutrition has called for mandatory fortification in the United Kingdom to replace voluntary fortification, together with guidance on high dose folic acid supplements, to increase the population folate concentrations while avoiding excessive intakes of folic acid.1 Large trials of folic acid supplements at doses 10 times higher than the average extra intake after fortification provide reassurance that such a policy is likely to be safe.10 11 12
Population surveys of RBC folate concentrations, along with the optimum threshold confirmed by Crider and colleagues, will help to guide these important policy decisions worldwide and allow public health leaders to monitor a population’s response with the ultimate goal of reducing the incidence of largely preventable neural tube defects.
Cite this as: BMJ 2014;349:g4810
Contributors: Both authors contributed to this editorial.
Competing interests: We have read and understood the BMJ policy on declaration of interests and declare the following interests: none.
Provenance and peer review: Commissioned; not externally peer reviewed.