B-Vitamin Form Guide
Methylfolate or folic acid? Methylcobalamin or cyanocobalamin? Pick a vitamin, add your MTHFR status and goal, and get a specific form, dose range, and label terms.
From genetic testing. Mainly affects the folate and riboflavin recommendations. Leave as "Not tested" if unsure.
Options change with the vitamin selected.
To find products that actually contain the recommended form, use the supplement ingredient search and search the label term shown above.
How this works
Whether a vitamin form matters depends on where the bottleneck sits in its activation pathway, and the bottlenecks differ sharply across the B vitamins.
Folate has a real one. Folic acid is a synthetic, oxidized precursor that must be reduced by dihydrofolate reductase (DHFR), an enzyme that is slow and saturable in human liver. Single doses above roughly 200 mcg begin to spill unmetabolized folic acid (UMFA) into circulation. L-methylfolate (5-MTHF) is the finished, circulating form; it bypasses both DHFR and the MTHFR enzyme, so it works identically whether you carry C677T variants or not. Homozygous C677T (TT, roughly 10 percent of many populations) cuts MTHFR activity by about 70 percent; heterozygotes lose about 35 percent. Even so, standard 400 mcg folic acid still raises blood folate and still prevents neural tube defects in TT carriers; methylfolate is a reasonable preference, not a medical necessity. The 1,000 mcg per day adult UL applies only to synthetic folic acid and folinic acid, not to food folate or 5-MTHF.
B12 is mostly a marketing battleground. All four supplemental forms lose their upper ligand inside the cell and converge on the same cob(II)alamin intermediate before being rebuilt into methylcobalamin and adenosylcobalamin as needed, which is why head-to-head evidence shows no consistent advantage for the coenzyme forms over cyanocobalamin. Dose matters more than form: without intrinsic factor, absorption falls back on passive diffusion at about 1 percent, which is why deficiency protocols use 1,000 mcg or more daily.
B6 is the safety story. Pyridoxine in sustained high doses causes sensory peripheral neuropathy; EFSA lowered the European tolerable upper intake to 12 mg per day in 2023 (the US UL remains 100 mg), working from a 50 mg per day reference point. P5P is the active coenzyme, but it is dephosphorylated at the gut wall before absorption, so it is not proven to avoid the risk.
B2 and B1 are absorption stories. Riboflavin transport saturates around 27 mg per dose, and plain riboflavin is what the 400 mg migraine trials used; R5P is dephosphorylated before uptake and offers no advantage. Thiamine transport saturates at a few mg, which is why benfotiamine, with roughly 3.6-fold higher bioavailability, is used in nerve-focused dosing, and TTFD is used when crossing into the brain matters.
References
Ferrazzi E, et al. Folic acid versus 5-methyl tetrahydrofolate supplementation in pregnancy. Eur J Obstet Gynecol Reprod Biol. 2020;253:312-319.
EFSA Panel on Nutrition (NDA). Scientific opinion on the tolerable upper intake level for vitamin B6. EFSA J. 2023;21(5):e08006.
Obeid R, et al. Cobalamin coenzyme forms are not likely to be superior to cyano- and hydroxyl-cobalamin in prevention or treatment of cobalamin deficiency. Mol Nutr Food Res. 2015;59(7):1364-1372.
Bozic I, et al. Thiamine and benfotiamine: Focus on their therapeutic potential. Heliyon. 2023;9(11):e21839.