Low levels of Vitamin B12 Increase Risk of Spina Bifida

Posted on: 04 March 2009

Children born to women who have low blood levels of vitamin B12 shortly before and after conception have an increased risk of neural tube defects such as spina bifida. The new findings by researchers at Trinity College Dublin, the Health Research Board of Ireland and the National Institutes of Health in the USA, were published in the March issue of Pediatrics.

The neural tube is the embryonic structure that gives rise to the spine and brain. Spina bifida which can cause partial paralysis, and anencephaly where the brain and skull are severely underdeveloped, are the two most common forms of neural tube defects. They currently affect about one in 1,000 pregnancies in Ireland.  Ireland has traditionally had a higher rate of these defects than many other countries. The study shows that women with the lowest B12 levels during early pregnancy were almost five times more likely to have a child with a neural tube defect compared to women with the highest B12 levels.

Commenting on the significance of the findings, Dr Anne Molloy of the School of Medicine at Trinity College Dublin and first author of the study said: “Researchers have known for over a decade that a woman’s chances of having a child with a neural tube defect can be greatly reduced by taking folic acid, the synthetic form of the B vitamin folate, during the weeks before and after conception. Vitamin B12 has an important influence on the way folate is used in the body and our results suggest that the two vitamins are jointly involved in influencing a woman’s risk”. 

Co-author, Professor John Scott of the School of Biochemistry and Immunology at Trinity College Dublin, a member of the National Committee on Folic Acid Food Fortification added: “It is generally agreed that folic acid supplements do not prevent all neural tube defects and it is likely that other factors can affect a woman’s risk. Our study suggests that women can reduce their risk further by ensuring that they have adequate B12 levels before they become pregnant”.

“We analysed stored blood samples that were collected during early pregnancy from three different groups of Irish women between 1983 and 1990. This time period is significant because it was a time when pregnant women in Ireland rarely took vitamin supplements. We found that the blood concentration of vitamin B12 was significantly lower in mothers who had babies with neural tube defects in contrast with normal pregnancies in all three groups”, explained Dr Peadar Kirke of the Health Research Board.

Unlike folic acid, the richest sources of vitamin B12 are meat and animal based foods so women who are strict vegetarians or who eat little meat or dairy foods are the most likely group to have low B12 levels, along with women who have intestinal disorders that prevent them from absorbing sufficient amounts of B12. The researchers suggested that women should have blood vitamin B12 concentrations above 300 ng/L before becoming pregnant and they called for further research to establish the intake of vitamin B12 that might ensure an effective level of protection. Currently, the Irish Department of Health and Children recommends that women who could become pregnant should take an extra 400 micrograms of folic acid daily before conception and during the first 12 weeks of pregnancy for the prevention of neural tube defects.

Because low blood folate levels are a known risk factor for neural tube defects, the researchers used statistical techniques to estimate the role of vitamin B12 independently of the role of folate. In all three groups, women with B12 concentrations below 250 ng/L, had 2.5-3 times the risk of having a child with a neural tube defect compared to those with higher levels. Women with levels in the deficient range (0-149 ng/L ) were at the highest risk: five times the risk of having a child with a neural tube defect compared to that of women with higher levels of B12.

The study was funded by the Health Research Board, Ireland and by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), one of the USA National Institutes of Health.  NICHD’s  Dr James Mills,   senior investigator in the Division of Epidemiology, Statistics, and Prevention Research and Principal Investigator of the joint research programme, said: “The formation of the neural tube occurs very early in pregnancy – before many women even realise they are pregnant. If women wait until they realise that they are pregnant before they start taking folic acid, it is usually too late. Similarly, it would be wise for all women of childbearing age to have a good vitamin B12 status, whether they are planning a pregnancy or not.”  

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