Slow human folic acid conversion may hamper supplement effectiveness
MedWire News: Clinical trials testing the benefits of folic acid supplementation during pregnancy to prevent neural tube defects and other diseases may be hampered by the low rate of conversion to useful metabolites by the human liver, say US scientists.
Steven Bailey and June Ayling, from the University of California in Berkeley, used human and rat liver samples to measure the activity of dihydrofolate reductase (DHFR). This converts folic acid to tetrahydrofolate (THF), which , in turn, performs all of the functions of folic acid.
Using 7,8-dihydrofolate as a substrate, the results showed that average human DHFR activity to form THF in the liver was almost 35 times lower than that seen in the rat liver, and that there was a five-fold variation in activity in human livers, compared with less than two-fold variation in rat livers.
Using folic acid as a substrate, the rate of formation of THF via DHFR was 850 times slower in the rat liver than when 7,8-dihydrofolate was used as a substrate. In human liver samples, the rate of conversion of folic acid was 1300 times slower when using folic acid compared with 7,8-dihydrofolate.
While acknowledging that lower folic acid doses may not be effective, the team concludes: “Our data... suggest that most of the folic acid given in the amount of the US Daily Value (0.4 mg) is converted to active folate in most individuals.”
MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a part of Springer Science+Business Media. © Current Medicine Group Ltd; 2009
By Liam Davenport