Infant vitamin B12 status and its predictors - cross-sectional baseline results from an ongoing randomized controlled trial.

Background: Vitamin B12 is a crucial micronutrient for infant growth and development.

Objective: The objective of this study was to describe vitamin B12 status in Norwegian infants aged 6-15 wk using multiple biomarkers and cut-off approaches, and to identify its predictors.

Methods: From November 2021 through August 2024, infants aged 6-15 wk and their mothers were recruited from public health clinics in Innlandet County, Norway, as part of an ongoing randomized controlled trial. Plasma cobalamin and methylmalonic acid (MMA) concentrations were analyzed among all infants in the cohort (n = 644), and total homocysteine (tHcy) concentrations were analyzed in a subgroup (n = 358). The combined indicator for vitamin B12 status (cB12) was calculated by Fedosov's equation. Low status was defined using multiple cut-off approaches. Potential predictors of infant vitamin B12 status were evaluated using regression models.

Results: Mean (standard deviation [SD]) infant age was 9.1 (1.8) wk. The median (interquartile range) concentrations were: cobalamin 242 (192, 322) pmol/L, tHcy 7.4 (6.2, 9.4) μmol/L, and MMA 0.34 (0.21, 0.77) μmol/L. The mean (SD) cB12 was -0.5 (0.7). Eight percent had cobalamin <148 pmol/L, and 40% <221 pmol/L. Sixty-seven percent had tHcy >6.5 μmol/L, 19% >10 μmol/L, and 4% >13 μmol/L. Sixty-four percent had MMA>0.26 μmol/L. Exclusively breastfed infants had 40% lower cobalamin and 30% higher tHcy compared with nonbreastfed infants. Partially breastfed infants had 21% lower cobalamin and 12% higher tHcy compared with nonbreastfed infants.

Conclusion: A substantial proportion of Norwegian infants have biochemical signs of low vitamin B12 status, given that the cut-offs were established in adults. Lower status was observed in partially and exclusively breastfed infants, compared with nonbreastfed infants. However, it is unclear whether these biomarker patterns have clinical significance. Further research is needed to determine consequences of low vitamin B12 biomarker concentrations in early infancy. This trial was registered as NCT05005897.