medwireNews: The US Preventive Services Task Force (USPSTF) has reaffirmed its 2009 recommendation that women who are planning or capable of pregnancy should take a daily supplement containing 400 µg to 800 µg of folic acid for the prevention of neural tube defects (NTDs).
The updated recommendation, published in JAMA, is based on a review of 24 studies, including 58,860 participants, of which 20 looked at the benefits and potential harms of folic acid supplementation for preventing NTDs.
Studies conducted prior to food fortification in the USA in 1998 demonstrated a clear benefit with folic acid, notably an 87% reduced risk in the incidence of NTDs in a randomized controlled trial, which was supported by cohort and case–control studies.
Given this evidence of benefit and the introduction of food fortification, no new prospective studies were conducted. Although recent case–control studies have not demonstrated a consistent protective benefit against NTDs with folic acid supplementation, the researchers, led by Meera Viswanathan (RTI International, Research Triangle Park, North Carolina, USA), say the observational data relied on in these studies are subject to selection and recall bias.
In a related editorial, James Mills (National Institutes of Health, Bethesda, Maryland, USA) points out that a lack of additional protection in the fortification era may mean that food fortification, which is estimated to provide 163 µg per day on average, may be sufficient and supplementation at the recommended 400 to 800 µg per day may be more than is needed.
But he adds that even if this is the case, there is still not enough known about how folic acid prevents NTDs to reject the USPSTF recommendation.
“For example, it is not known whether the tissue stores of folate in the developing embryo or the availability of folate in the serum during the all-important few days of neural tube closure is most important,” he explains, adding: “ Habitual use of folic acid supplements is a more reliable method of ensuring adequate levels than diet.”
Indeed, the USPSTF members point out that evidence indicates that “most women are not consuming fortified foods at the level needed for optimal benefit.”
Mills therefore believes the USPSTF recommendation “is a prudent one.”
The benefits of folic acid supplementation were in balance with any potential harm to the mother or infant, which on evidence was “no greater than small,” the members report. Specific data, for instance, indicated no increased risk for twinning or asthma.
The USPSTF acknowledges that there was no consistent evidence regarding the best timing, but give a critical period of at least 1 month before conception through the first 2 to 3 months of pregnancy.
Limitations of the evidence meant that the benefits of folic acid supplementation other than averting NTDs and its effect in high-risk women could not be assessed.
By Lucy Piper
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