A blood test may show high or normal-high B9 levels even with out supplementation. And that is why UMs need 5MTHF. But OMs should not take 5MTHF.
Wikipedia says-
"L-methylfolate is the natural, active form of folate used at the cellular level for DNA reproduction, the cysteine cycle and the regulation of homocysteine among other functions. 'The un-methylated form, Folic Acid (vitamin b9) is found in leafy green vegetables. Synthetic folic acid works to replicate the action of folate; but must be broken down in a series of metabolic steps in order to become L-methylfolate. Approximately 10% of the general population (homozygous TT) lack the enzymes needed to receive any benefit from folic acid. Another 40% of the population (heterozygous CT) appear to convert only a limited amount of folic acid into L-methylfolate. They cannot fully process supplemental folic acid at RDA or higher dose levels. The remaining population do not have an MTHFR polymorphism and can fully metabolize folic acid."
50% of the population is undermethylators. Why would it be harmful for a normal methlyator to take 5MTHF, the actual natural form used at the cellular level? Why isn't it reasonable to switch to 5MTHF and cover 100% of the population?
