Women with low levels of vitamin B12 have up to five times the normal risk of having a baby with a major birth defect, new research shows.
It's long been known that another nutrient, folic acid, lowers the risk of neural tube defects — devastating malformations of the brain and spine, including spina bifida.
Now researchers are reporting that women who have low vitamin B12 levels shortly before and after they get pregnant are at significantly greater risk of delivering a child with a neural-tube defect.
Vegans and women who eat little or no meat, fish, eggs, milk or cheese are at the highest risk, as are women with stomach or intestinal problems, including inflammatory bowel disease, that keep them from absorbing enough B12.
The finding needs to be confirmed by more studies. But the researchers say women at risk should be tested for B12.
"Nobody should get pregnant with low vitamin B12 levels," said Dr. James Mills, a senior investigator with the U.S. National Institute of Child Health and Human Development. "Women who are on diets that exclude animal products should check with their physician before they get pregnant."
It's the second time in recent years scientists have warned women about adequate vitamin B12. Researchers from St. Michael's Hospital in Toronto reported two years ago that low vitamin B12 triples the risk of neural-tube defects. It's estimated about one-third of neural tube defects in Canada may be due to B12 deficiencies.
The vitamin is important for healthy nerve cells and red blood cells. It's also needed to help make DNA.
Neural-tube defects occur early in pregnancy. The embryo forms a brain and spinal cord by essentially folding a flat portion of embryo into a tube.
If that tube doesn't close completely, the result is either spina bifida, which can cause paralysis, or anencephaly, a defect of the brain and skull that is "uniformly fatal early in infancy or before," Mills said. Some affected babies are delivered stillborn.
"This neural tube rolling up and closing is completed by the 28th day of pregnancy.
A lot of women don't even know they're pregnant by that point," Mills said.
Folic acid can prevent up to three-quarters of neural-tube defects, and the incidence rate in Canada has dropped by nearly half with more prenatal screening and the mandatory folic-acid fortification of white flour, enriched pasta and cornmeal. The rate has fallen from 10 per 10,000 live births in 1991 to 5.8 per 10,000 births in 1999.
Vitamin B12 is closely related to folic acid, Mills says. Mills' team wanted to know, just how much vitamin B12 women need to be protected from the risk for neural-tube defects.
They went to Ireland, where the high rate of neural-tube defects has been called the "Curse of the Celts," a phenomenon Mills says is due to a combination of genes and diet.
For their study, researchers tested blood samples collected during early pregnancy from three groups of Irish women: two groups were carrying a child with a neural-tube defect and the third group of women had already had one child born with a neural-tube defect and were at risk for another. There were 278 women in total.
The researchers measured the women's vitamin B12 and folate levels and compared them to "control" pregnant women who were not carrying a baby with a neural-tube defect.
In all three groups, women with low B12 concentrations had between a two- and threefold higher risk of having a baby with a neural-tube defect compared to women with higher levels.
Women with levels in the deficient rate were five times more likely than women with higher levels to have a baby with a neural tube defect.
Overall, the researchers say women who start pregnancy with blood levels of B12 below 300 ng/L are at "significantly higher risk" for neural-tube defects.
The study appears in the journal Pediatrics.
Women are already advised to take folic acid if planning a pregnancy.
"The point that we're making in our study that's new is that women also should be aware of the fact that they need adequate B12," Mills said in background material released with the study.
All women of child-bearing age should consume the recommended amount of vitamin B12, whether or not they're planning to get pregnant, Mills says.
Health Canada recommends adults receive 2.4 micrograms of B12 daily.