Vitamin B12 and folate deficiency in obese pregnant women

Vitamin B12 and folate are especially important for foetal growth and development

As obesity rates rise in the general population, they also rise in pregnant women.

During the past 20 years, the percentage of women who are obese at the beginning of their pregnancy care has more than doubled to more than 15%. In addition to the general health risks of obesity, pregnant women are at risk for pregnancy specific challenges.

One of the main concerns is that obesity increases risk of nutritional deficiencies which, in turn, can have serious implications for the health of both the mother and the foetus.

Vitamin B12 and folate are especially important for foetal growth and development. Deficiency is associated with a number of foetal abnormalities and birth defects, as well as megaloblastic anaemia in the mother.

An Indian study found an association between higher maternal body mass index (BMI) and lower B12 levels, but the study did not determine whether differences in diet, vitamin supplements or other factors affected the association.

British researchers sought to clarify the relationship between BMI and serum B12 and folate in a UK pregnancy cohort. To do that, they studied data collected at 28 weeks gestation in nondiabetic, singleton, white pregnancies and looked for associations between levels of the two nutrients, obesity and related glycemic and metabolic biomarkers.

The resulting paper, published in 2015 in PLoS One, confirmed the findings of the earlier Indian study. Higher BMI at 28 weeks gestation was associated with lower circulating vitamin B12 and folate. In fact, for every 1% increase in BMI, there was a 0.6% decrease in circulating B12. Other biomarkers of body fat metabolism were also independently associated with circulating B12.

Although these findings do make clear an association between obesity and decreased levels of B12 and folate, it’s not clear whether this is a causal relationship — and, if so, whether it’s the obesity that causes the deficiencies or vice versa. Still, given the significant health risks to both mother and foetus related to deficiencies in these nutrients, it may be especially important for obese women to supplement during pregnancy.