DHFR and anemia: Future studies should investigate the effect of long-term supplementation of (6S)-5-Methyl-THF-Na versus (6S)-5-Methyl-THF-Ca and folic acid on intracellular folate levels (RBC-folate), biochemical markers (i.e., lowering tHcy), and clinical endpoints such as correction of anemia especially in relation to the presence of polymorphisms in the MTHFR and DHFR genes.