Fortification of grains to reduce the risk of neural tube defects should include vitamin B12 along with folic acid, says a new study from Canada.
"There was almost a tripling in the risk for NTD in the presence of low maternal B12 status," wrote the researchers in the journal Epidemiology. "The benefits of adding synthetic B12 to current recommendations for periconceptional folic acid tablet supplements or folic-acid-fortified foods need to be considered."
The connection between folate deficiency in early pregnancy and an increased risk of neural tube defects (NTD) - most commonly spina bifida and anencephaly - in infants led to the 1998 introduction of public health measures in the US and Canada, where all grain products are fortified with folic acid - the synthetic, bioavailable form of folate.
While preliminary evidence indicates that the measure is having an effect with a reported 15 to 50 per cent reduction in NTD incidence, parallel measures in European countries, including the UK and Ireland, are still on the table.
However, one of the arguments against the introduction of such measures in Europe has been that folate consumption in excess of 1000 micrograms per day could delay the detection of vitamin B12 deficiency in older people, which can have severe neurological consequences.
The new study, led by David Cole from the University of Toronto, looked at the effect of low maternal vitamin B12 status as a risk factor for neural tube defects. The researchers state that previous studies did not adjust for folate levels, and were conducted in countries without folic acid food fortification.
Eighty-nine women with a NTD (cases) and 422 unaffected pregnant controls were recruited in Ontario, and blood samples taken in order to measure levels of holotranscobalamin (holoTC), a sensitive indicator of B12 status. Measurements were taken at 15 to 20 weeks' gestation.
The researchers found that the average holoTC levels in cases were 67.8 pmol/L and 81.2 pmol/L in controls. A trend was observed for an increasing risk of NTD amongst women with lower levels of holoTC. Indeed, the difference lowest versus highest quartile was associated with an increased risk of NTD of 190 per cent.
"It remains to be determined what fraction of NTD cases in a universally folate-fortified environment might be prevented by higher periconceptional intake of B12," concluded the researchers.
May 2007, Volume 18, Number 3, Pages 362-366
"Vitamin B12 and the Risk of Neural Tube Defects in a Folic-Acid-Fortified Population"
Authors: J.G. Ray, P.R. Wyatt, M.D. Thompson, M.J. Vermeulen, C. Meier, P.-Y. Wong, S.A. Farrell, D.E.C. Cole