In a research carried out by Keith M. Godfrey et al., supplementing with over-the-counter doses significantly decreased the occurrence of deficiency indicators before and during pregnancy. Additionally, it led to sustained higher levels of maternal plasma vitamin B12 during the recommended lactational period.  The study aimed to examine the longitudinal trends in maternal vitamin levels, spanning from preconception through early and late pregnancy to six months post-delivery, and evaluate the influence of vitamin supplementation.

In this prespecified secondary assessment of the NiPPeR double-blind randomized controlled trial, 1729 women between the ages of 18 and 38, who intended to conceive, were enrolled. Participants were randomly allocated to receive either a standard vitamin supplement (control group; n=859) or an improved version (intervention group; n=870) from preconception through pregnancy. The study included common components such as β-carotene, folic acid, calcium, iron, and iodine. The intervention group received additional components like vitamins B6, riboflavin, B12, and D, probiotics, myoinositol, and zinc.

The primary endpoint of the study was glucose tolerance at twenty-eight weeks of gestation, determined through an oral glucose tolerance test. Additionally, the secondary endpoint emphasized the decrease in maternal micronutrient insufficiency, specifically in vitamin D, riboflavin, vitamin B6, and vitamin B12 both before and during pregnancy. In this study, maternal plasma levels of vitamin D, B-vitamins, and markers indicating insufficiency or deficiency (such as hydroxykynurenine-ratio, homocysteine, methylmalonic acid) were assessed at various stages: at recruitment, one month after initiating the preconception intervention, during early pregnancy (7 to 11 weeks gestation), late pregnancy (around twenty-eight weeks gestation), and post-delivery (six months after discontinuing supplements).

Researchers assessed longitudinal changes, utilizing standard deviation score (SDS) to compare differences between the control and intervention groups. Upon enrollment, participants showed varied deficiencies: 29.2% had marginal or low folate (<13.6 nmol/L), 7.5% (<5 nmol/L) and 82.0% (≤26.5 nmol/L) for riboflavin, 9.1% for vitamin B12 (<221 pmol/L), and 48.7% for vitamin D (<50 nmol/L). Proportions were balanced between groups. At the time of recruitment, more than 90% of the participants exhibited deficient or insufficient levels of one or more of these vitamins. In the control group, riboflavin plasma concentrations decreased during both early and late pregnancy, while 25-hydroxyvitamin D levels remained stable in early pregnancy.

The plasma levels of vitamin B6 and B12 consistently decreased during pregnancy, reaching more than 1 SDS below the baseline by the 28th week of gestation. Notably, 54.2% of participants in the control group experienced low vitamin B6 concentrations (<20 nmol/L) in late pregnancy.  Following one month of supplementation, participants in the intervention group exhibited significantly elevated plasma concentrations of supplement components compared to those in the control group (Table 1).

The intervention arm showed a decrease in markers of vitamin inadequacy, and the prevalence of vitamin D insufficiency (<50 nmol/L) during late pregnancy was notably lower in the intervention group (8.5% versus 35.1%). Additionally, even six months post-delivery, plasma vitamin B12 levels remained at a superior level in the intervention arm compared to the control arm, with an increase of 0.30 SDS (0.14, 0.46).

Over 90% of subjects in the trial exhibited marginal or low concentrations of riboflavin, folate, vitamin D, or vitamin B12 during preconception, and a considerable number of subjects developed markers indicating vitamin B6 deficiency in late pregnancy. Thus, using over-the-counter supplements before and during pregnancy remarkably reduces the risk of vitamin deficiency. It also helps sustain higher levels of maternal plasma vitamin B12 during breastfeeding.