Folic acid vs 5-MTHF: why the form of B9 changes everything
Many people supplement with vitamin B9 without getting the benefit they expect. The reason lies in a simple biochemical reality that is rarely explained: this vitamin exists in several forms, and not all of them are equivalent.
Folate and folic acid: two distinct molecules
These two terms are often used interchangeably, yet they refer to two different chemical realities.
Folate is the natural form, found in green leafy vegetables, legumes and liver. Once absorbed, the body converts it into several active forms, the main one being 5-methyltetrahydrofolate (5-MTHF, or levomefolate). Folic acid, by contrast, is the synthetic form developed in the 1940s. It is used in the vast majority of common supplements and in the mandatory flour-fortification programmes practised in some countries.
For folic acid to be usable by cells, it must pass through four enzymatic conversion steps; the last is catalysed by the enzyme MTHFR (methylenetetrahydrofolate reductase).
The MTHFR polymorphism
About 40% of the population carries at least one polymorphism of the MTHFR gene (the most studied variants are C677T and A1298C). This polymorphism measurably reduces enzyme activity: by around 30% in heterozygous carriers, and by 60 to 70% in homozygous carriers.
For these individuals, synthetic folic acid is only partially converted; the rest circulates as UMFA (unmetabolised folic acid), an inactive fraction with no documented physiological effect. Supplementation then loses a significant part of its functional relevance.
The biological functions of 5-MTHF
5-MTHF is the central methyl-group donor in several fundamental processes: the synthesis of neurotransmitters (serotonin, dopamine); the remethylation of homocysteine into methionine, which influences cardiovascular and cognitive risk; cell replication and DNA repair; the formation of red blood cells and the binding of iron to haemoglobin; the development of the neural tube during the first trimester of pregnancy.
Insufficient methylation can show up as persistent fatigue, a slowed mental state, unstable mood or an elevated homocysteine level on blood work. These signs warrant evaluation by a practitioner competent in micronutrition or orthomolecular medicine.
5-MTHF: the directly active form
5-MTHF is the biologically active form of folate. It is taken up directly by all cells, with no dependence on the MTHFR enzyme. Its functional advantages are documented: genotype-independent absorption, no unmetabolised fraction, effectiveness in carriers of the polymorphism, and more efficient placental transfer than synthetic folic acid.