Cross-referencing clinical data
A pairing appears on this page only when a trial gave both ingredients together and measured the result. Vitamin B9 (5-Methyltetrahydrofolate) has none that clears that bar.
Stitching two separate single-ingredient studies into a pairing is the one thing this engine will not do. When a study of the combination itself holds up at source, it lands here with its citation.
No invented synergy. Where actives were studied on their own rather than together, the record shows each on its own evidence, never a combined effect no trial measured.
Research strength. Research strength says how much work stands behind the combination. It is never a product score.
Independent record. Every finding is cited to a named trial, dated, and never written by the brand.
20 pairings are live across the library today. Checked 20 July 2026.
No study gave these as a pair, so they are not in the card above. But the reason they belong together is settled biochemistry, not a guess, so it is worth knowing.
5-MTHF donates its methyl group to homocysteine only through methionine synthase, and that enzyme needs methylcobalamin as its cofactor. Without adequate B12 the methyl group stays stuck on folate, a state described as the methyl trap. High folate intake can also normalise the blood picture of B12 deficiency while nerve involvement continues, which is why the two are usually assessed together.
5-MTHF clears homocysteine by remethylating it back to methionine. P5P, the active form of B6, drives the other exit route, cystathionine beta-synthase, which sends homocysteine down to cysteine. The two routes handle different loads, so B-complex formulas usually carry both.
MTHFR is a flavoprotein and holds FAD, made from riboflavin, as its cofactor. That matters mostly for people converting folic acid or dietary folate into 5-MTHF, since supplemental 5-MTHF is already past that step. Riboflavin status still shapes how the wider folate cycle runs.
Betaine remethylates homocysteine through betaine-homocysteine methyltransferase, a route that runs in liver and kidney and does not need folate or B12. It works alongside the 5-MTHF route rather than through it. Formulas aimed at methylation support commonly pair them for that reason.
Folic acid is a synthetic oxidised form that must pass through dihydrofolate reductase before it becomes usable, while 5-MTHF is already the circulating form. Both use the reduced folate carrier and folate receptors, so they compete for uptake. Unmetabolised folic acid appearing in blood at higher intakes reflects the limited capacity of that reduction step.
Intestinal folate conjugase, which strips the polyglutamate tail off dietary folates, is a zinc-dependent enzyme. Supplemental 5-MTHF arrives as a monoglutamate and skips that step, so the dependency applies mainly to food folate. Very high folate intakes have also been reported to interfere with zinc absorption, though findings are inconsistent.
Choline is oxidised to betaine and feeds the same methyl pool that 5-MTHF supplies. When folate intake is low the body draws harder on choline, and the same is true in the other direction. Requirements for one shift with the status of the other.
Methylfolate and 5-methyltetrahydrofolate name the same molecule, sold under salt forms such as calcium L-5-MTHF and glucosamine L-5-MTHF. Stacking both means doubling one nutrient without knowing it. Anyone combining products should add the labelled amounts together.
Reduced folates oxidise readily in air, light and acid. Ascorbate is a common antioxidant partner in folate formulations and in the assay chemistry used to measure serum folate. The pairing is formulation convention rather than a claimed clinical effect.
Nothing specific on file for Vitamin B9 (5-Methyltetrahydrofolate). Match the label to the daily amount above, and tell your doctor what you take.
Not medical advice. Show the label to your pharmacist.These are the studies our verdict leans on, chosen from the 2 we read for Vitamin B9 (5-Methyltetrahydrofolate). The full linked list is below.
FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. This information is for educational purposes only and is not intended to diagnose, treat, cure, or prevent any disease. Consult your healthcare provider before starting any supplement regimen.