Postnatal decline in pyridoxal phosphate and riboflavin. Accentuation by phototherapy.

Riboflavin is a cofactor in the conversion of pyridoxine (vitamin B6) to pyridoxal phosphate (PALP), an essential coenzyme in numerous metabolic pathways, including neurotransmitter synthesis. Riboflavin and pyridoxine are light sensitive in vitro, and conflicting results have been reported on the in vivo effects of phototherapy on riboflavin. We studied 25 full-term neonates receiving phototherapy and 16 healthy controls to evaluate their riboflavin and PALP status. Both vitamin cofactors decreased in both sets of infants, but significantly more so in the irradiated group. While the biologic or clinical importance of a modest biochemical decline in the level of PALP has not been established, it is possible that transient behavioral changes in irradiated, jaundiced neonates could be mediated by decreased availability of PALP. The mechanism for the postnatal decline and the desirability of routine supplementation with pyridoxine, especially in irradiated infants, require further study.