Assessment of vitamin B-12, folate, and vitamin B-6 status and relation tosulfur amino acid metabolism in neonates

Background: Total serum homocysteine (tHcy) has been used as an indicator o f intracellular vitamin B-12, vitamin B-6, and folate status in adults, but data for neonates and infants are lacking. Vitamin B-12 deficiency way hav e fatal effects on neurologic development in infants; therefore, early diag nosis is crucial. Objective: Our aim was to provide a reference range for tHcy in neonates an d to explore the relation of tHcy to 1) serum vitamin concentrations, 2) th e product of the transsulfuration pathway (cysteine), and 3) nutritional fa ctors. Design: tHcy, cysteine, folate, vitamin B-12, and vitamin B-6 were measured in 123 healthy, breast-fed neonates. The influence of nutrition (formula o r human milk) on these variables was investigated in 60 infants. Results: The mean (+/-SD) tHcy concentration was 7.8 +/- 3.1 mu mol/L. tHcy showed a linear association with log vitamin B-12 (r = - 0.64, P < 0.001), red blood cell folate (r = -0.33, P < 0.001), and cysteine (r = 0.35, P < 0.001). The strongest linear association was found between tHcy and the rat io of log cysteine to log vitamin B-12 (r = 0.71, P < 0.0001). We found mor e neonates with probable tissue deficiencies of vitamin B-12 and folate on the basis of tHcy measurements than was expected from the analysis of serum vitamin concentrations alone (15.4% compared with 9.7%). Breast-fed infant s had significantly lower vitamin B-12 concentrations and significantly hig her serum tHcy and cysteine concentrations and ratios of log cysteine to lo g vitamin B-12 than did formula-fed infants (P < 0.001). Conclusions: tHcy can be used as a functional indicator of vitamin B-12 and folate status in neonates. The ratio of cysteine to vitamin B-12 can be us ed as an additional index of impaired intracellular Hcy metabolism. tHcy an d cysteine concentrations in infants are affected by nutritional factors.