Assessment of vitamin B6 status in never-pregnant, pregnant and postpartum women and their infants

Abstract

Purpose Pyridoxal 5´-phosphate (PLP) is the main form of vitamin B6 in humans and functions a coenzyme for more than 160 different enzymatic reactions. The purpose of the study was to find plasma PLP concentrations, which ensure an optimal vitamin B6 status determined by a metabolic marker, in never-pregnant, pregnant and lactating women and their infants. Methods In an observational, prospective study, plasma PLP and the metabolic marker, HKr (hydroxykynurenine/(kynurenic acid + anthranilic acid + xanthurenic acid + hydroxyanthranilic acid) were assessed in women (n = 114) from pregnancy week 18 to 6 months postpartum and related to infant status. Never-pregnant women 18–40 years (n = 127) were included as controls. Results Compared to controls, plasma PLP decreased during pregnancy and increased postpartum, while HKr increased from week 18 to 6 weeks postpartum, indicating maternal vitamin B6 insufficiency during this period. In never-pregnant women, HKr increased gradually with plasma PLP < 100 nmol/L, and in pregnancy week 28 a sharp increase in HKr was seen at plasma PLP < 30 nmol/L. Despite correcting for maternal vitamin B6 status, infant median plasma PLP decreased with months of exclusive breastfeeding. Conclusions Plasma PLP and kynurenine concentrations differ substantially between never-pregnant, pregnant and postpartum women and infants. A plasma PLP concentration in the range of 50–100 nmol/L seems to ensure an optimal vitamin B6 status for never-pregnant women, whereas a plasma PLP > 30 nmol/L in pregnancy week 28 ensures an adequate vitamin B6 status during pregnancy and lactation. Infant vitamin B6 status at age 6 months is inversely correlated to number of months of exclusive breastfeeding.

Vitamin B6: a scoping review for Nordic Nutrition Recommendations 2023

“…The vitamin B 6 intake of breastfeeding mothers has been shown to be a strong predictor of infant status (38). However, in a recently published study, infant median plasma PLP decreased with months of exclusive breastfeeding, despite correcting for maternal vitamin B 6 status (28).…”

“…Plasma PLP decrease throughout pregnancy and increase postpartum, while the metabolic marker HKr increase from week 18 to 6 weeks postpartum, indicating maternal vitamin B 6 insufficiency during this period (28). In a study published in 1992, plasma PLP was substantially higher in the new-born, while the maternal plasma PLP concentration was 22.2 nmol/L, the concentration in venous cord plasma was 112.1 nmol/L (29), indicating that pregnant women have an increased requirement for vitamin B 6 .…”

“…2). Studies on changes in patterns of plasma metabolites, including organic acids and amino acids, in people with plasma PLP less than 30-50 nmol/L suggest that these PLP concentrations should be viewed as inadequate (28,43,44). In pregnancy week 28 a sharp increase in HKr was seen at plasma PLP<30 nmol/L (28).…”

“…The estimated average requirement (AR) of vitamin B 6 for adult men and women was set at 0.013 mg/g dietary protein. However, a recent publication shows that higher plasma PLP concentrations are associated with a better metabolic status (28). A plasma PLP concentration in the range of 50 -100 nmol/L seems to ensure an optimal vitamin B 6 status for never-pregnant women, whereas a plasma PLP > 30 nmol/L in pregnancy week 28 ensures an adequate vitamin B 6 status during pregnancy and lactation (28).…”

“…Plasma PLP concentrations are reported to decrease during pregnancy and increase postpartum, while the metabolic markers HKr increase from week 18 to 6 weeks postpartum, indicating maternal vitamin B 6 insufficiency during this period (28). There is, however, no agreement if this merely reflects physiological changes or maternal deficiency.…”