Lee Swanson Research Update

Low B-12 Levels in Mothers May Increase Risk of Defects in Babies

March 2009

Women with low blood levels of vitamin B-12 are at increased risk of having a child with neural tube defects, according to the findings of a new study.

The risk of neural tube defects was found to be five times higher among women with the lowest levels of vitamin B-12, compared to women with the highest B-12 levels, report researchers from the U.S. National Institutes of Health and Ireland’s Trinity College and the Health Research Board of Ireland. The study was published in Pediatrics.

The importance of B vitamins, particularly folate, in fetal development is well established. Currently, supplementation with folate or folic acid is recommended to all women of child-bearing age since most neural tube defects (NTDs), including spina bifida and anencephaly, occur within the first 22 to 28 days of pregnancy, when the mother-to-be is not aware that she is even pregnant.

Folic acid supplements after this time are too late to prevent neural tube defects and therefore fail to benefit women with unplanned pregnancies—more than half of all pregnancies in the U.S.

The new study indicates that women of child-bearing age should also be ensuring adequate intakes of vitamin B-12, a vitamin that may be lacking for women following a vegetarian or vegan diet.

The researchers looked at blood levels of vitamin B-12 among 278 women in Ireland between 1983 and 1990. During that time, pregnant women in Ireland rarely took vitamin supplements. The women included 171 women who were pregnant with a child having a neural tube defect at the time the blood was taken, and a second group of 107 women who had previously given birth to a child with a neural tube defect but whose current pregnancy was not affected.

After accounting for folate levels, a known risk factor for NTDs, the researchers calculated that women with low B-12 concentrations (estimated at less than 250 nanograms per liter before pregnancy) had 2.5 to 3 times greater chance of being the mother of a child affected by neural tube defect.

Furthermore, women with B-12 deficiency (blood levels between 0 and 149 ng/L) had five times the risk of having a child with a NTD compared to those with higher levels.

"We suggest that women have vitamin B-12 levels of [more than] 300 ng/L (221 pmol/L) before becoming pregnant. Improving B-12 status beyond this level may afford a further reduction in risk, but this is uncertain," they concluded.

Pediatrics 123(3):917-923, 2009

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