Vitamine B12 bij zwangerschap*
Uit twee studies waarvan een onder 1.200 zwangere Ierse vrouwen blijkt dat niet alleen goede bloedwaarden foliumzuur doch ook goede bloedwaarden vitamine B12 belangrijk zijn op het moment van
zwanger worden. Vrouwen met bloedwaarde vitamine B12 van lager dan 250 pg/ml hadden wel drie keer meer kans op een embryo met een neuraalbuisdefect dan zij met bloedwaarden van 300 pg/ml en hoger. Een neuraalbuisdefect is een aandoening aan de neurale buis die ontstaat tijdens de embryonale ontwikkeling. Zo ontstane defecten hebben een enorme invloed op de verdere ontwikkeling van het embryo. Vrouwen die dus zwanger willen worden kunnen dus het beste behalve extra
foliumzuur ook extra vitamine B12 nemen.
Vitamin B12 Deficiency in Pregnant Women Linked to Birth Defect
A study recently published in the journal Pediatrics has revealed that women who do not have an adequate intake of vitamin B12 during pregnancy are at greater risk of having a child with a birth abnormality called neural tube defect.
About Folic Acid, Vitamin B12 and Birth Defects
The researchers had noted that folic acid fortification in food had helped to lower the prevalence of neural tube defects by about 50% to 70%. As it was not likely that levels of folic acid added would be increased anymore to further help prevent neural tube defect occurrence, they set out to investigate another modifiable risk factor - vitamin B12. This nutrient was chosen due to the fact that it was metabolically related to folic acid, and also because previous research had suggested that mothers who gave birth to babies affected by the condition tended to have low levels of
it.
Details and Findings of Study
For the study, the team looked at data on pregnancy vitamin B12 levels of close to 1,200 Irish women, at a time when food fortification or consumption of vitamin supplements was still uncommon. Three separate groups of women, each having a sub-group of pregnancies hit by neural tube defect and a sub-group which acted as controls, were used. The first group compared with controls women when they had a pregnancy affected by neural tube defect; the second group compared with controls women who had previously been affected by the condition but whose present pregnancy was not; and the third group was similar to the first
group.
The researchers found that women whose children had been affected by the said defect had markedly lower levels of vitamin B12 in their blood. This was consistent throughout the three groups. After adjustment, the risk of a woman in the lowest vitamin B12 quartile having a child hit by neural tube defect was two to three times that of a woman in the highest quartile.
Highest risks were found for women who had pregnancy blood vitamin B12 levels of less than 250 ng/L. The study team suggested that, to reduce their risk of having pregnancies affected by neural tube defect, women boost their vitamin B12 levels to above 300 ng/L (or 221 pmol/L) before conceiving. Having sufficient amounts of folic acid and vitamin B12 before getting pregnant is important, because these nutrients seem to be most vital in an embryo's first few days and weeks. And, as about half of all pregnancies are not planned, women of childbearing age are currently advised to consume at least 400 micrograms of folic acid each day.
Findings of another Study in Canada
The findings of this study were mirrored in those of another recent study which was conducted in Canada and published in the American Journal of Clinical Nutrition. The researchers in the Canadian study had found that the risk of neural tube defects was three times as high in pregnant women whose vitamin B12 levels were in the lower quartile; this applied whether the data was collected before or after folic acid fortification took place in the country. They concluded that their findings suggest vitamin B12 fortification may help cut the rate of neural tube defects more than folic acid fortification alone.
Vegans Are More At Risk of Vitamin B12 Deficiency
Vitamin B12 is commonly found in meats, milk, cheese and eggs. As the vitamin does not occur naturally in plant foods, vegans tend to be at higher risk of being deficient in
it.
The Vegetarian Resource Group (VRG) is a non-profit organization which is dedicated to educating the public on vegetarianism and connected issues such as health, nutrition, ecology, ethics and world hunger. According to them, possible sources of vitamin B12 for vegans include certain sources of nutritional yeast, fortified cereals, fortified soy milk, fortified meat analogues (foods made using wheat gluten or soybeans to resemble animal flesh), as well as vitamin B12 supplements. Foods such as tempeh, miso and sea vegetables are sometimes said to have vitamin B12, although they are not considered reliable sources of it.
References
Molloy AM et al. Maternal Vitamin B12 Status and Risk of Neural Tube Defects in a Population With High Neural Tube Defect Prevalence and No Folic Acid Fortification.
Pediatrics 2009;123(3):917-923.
Thompson MD et al. Vitamin B-12 and neural tube defects: the Canadian experience. American Journal of Clinical Nutrition 2009;89(2):697S-701S.
"Vitamin B-12 deficiency tied to neural tube birth defects" by Liz Szabo, USA Today.
Vegetarian Resource Group website (VRG.org) (Mei
2009)
