Clinical note · Methylation
A nutrient on a label is not the same as a nutrient in an enzyme. Between the bottle and the reaction lie conversion steps, and that is where individual differences arise.
Clinical note. No doses are given — they are determined individually after measurement.
4.87 ★★★★★ Highest rated in Sweden Verified patient reviews · Reco.se Reco.seVerifiedIn short: choose the already-active form wherever a conversion step may be impaired — 5-MTHF for folate, P5P for B6, riboflavin for MTHFR. But form alone is not enough. Correct one node and flux rises until the next node becomes limiting, and the patient experiences the supplement as having stopped working. Full compensation means every node needing support receives it simultaneously — and which those are is determined by genotype and measurement, not by supplying everything.
A nutrient on a label is not the same as a nutrient in an enzyme. Between the bottle and the reaction lie absorption, transport and in many cases one or more conversion steps — and it is in the conversion steps that individual differences arise.
Synthetic folic acid must be reduced and methylated before the cell can use it. Pyridoxine must be phosphorylated to P5P. Riboflavin must be converted to FAD. Each such step is an enzyme, and every enzyme can be impaired by genetics, by missing cofactors or by load.
Choosing a form that is already active means bypassing a step that might otherwise be the bottleneck. That is the entire point — and also the limit of what form selection can achieve: it solves the conversion problem, not every other problem.
| Node | Function | Form used | Cofactors |
|---|---|---|---|
| MTHFR | Produces active folate | 5-MTHF (methylfolate) | Riboflavin as FAD, NADPH |
| MTR | Remethylates homocysteine | B12 — several forms exist | Zinc, 5-MTHF as methyl donor |
| MTRR | Restores oxidised cobalamin | No substance of its own — requires SAM | SAM, NADPH, riboflavin (FAD/FMN) |
| BHMT | Folate-independent remethylation | Betaine (TMG); choline as precursor | Zinc |
| CBS | Initiates transsulfuration | P5P (pyridoxal-5-phosphate) | Haem, serine |
| AHCY | Produces homocysteine from SAH | No substance — requires NAD⁺ | Tightly bound NAD⁺ |
| MAT | Forms SAM from methionine | Methionine; magnesium | ATP, magnesium |
| SHMT | Supplies the folate cycle with one-carbon units | Serine, glycine | P5P |
MTHFR. Synthetic folic acid requires conversion. Riboflavin stabilises the thermolabile C677T enzyme.
MTR. B12 occurs as cyano-, hydroxo-, methyl- and adenosylcobalamin. They differ in stability, half-life and how they enter cellular cobalamin metabolism.
MTRR. This node cannot be supplemented directly. It is supported indirectly by maintaining the SAM pool and reducing capacity — which is why B12 alone is often insufficient.
BHMT. High betaine doses have raised LDL and total cholesterol in trials. Dose under follow-up.
CBS. Pyridoxine HCl must be phosphorylated to P5P, a step that can be impaired. P5P is the form the enzyme actually uses.
AHCY. The enzyme carries NAD⁺ as a fixed cofactor. At the same time NAD⁺ precursors drain methyl groups via NNMT. The relationship runs both ways, which makes this node particularly unwise to ignore.
MAT. Without sufficient SAM production, both methylation and MTRR restoration stall.
SHMT. Frequently overlooked. Without one-carbon units there is nothing to methylate the folate with.
This is the real content of the text, and it follows directly from T1: in a system of non-substitutable steps, function is determined by the most limiting step.
If folate is the bottleneck and you supply active folate, flux rises — until the next step becomes limiting. If B12 status is low, MTR becomes the new bottleneck. If B6 is low, the drain toward transsulfuration is narrow and homocysteine remains despite remethylation now working. If riboflavin is low, MTHFR still operates below capacity even with folate supplied.
The consequence is that partial compensation often produces an initial improvement that plateaus. The patient describes it as the supplement having stopped working. It did not — the bottleneck moved.
Full compensation means every node has what it requires, in a form it can use, simultaneously. Which nodes actually need support in a given person is determined by genotype and measured intracellular status — not by supplying everything.
An active form is not automatically the right choice. Without an MTHFR variant there is no bottleneck to bypass, and high doses of active folate can then drive methylation faster than downstream capacity allows — increasing the draw on methyl groups, methionine, B12, B6 and choline.
The same logic applies to methyl donors generally. Someone with a well-supplied system gains nothing from more; someone with a loaded system can develop symptoms from increasing the load without opening the drains at the same time.
This is why the question is never which supplement is best but what is limiting this particular person.
Homocysteine is the cheapest and most accessible readout of whether compensation is working. It is blunt — it does not identify which node is restricting — but it answers whether flux has improved.
Reassess after eight to twelve weeks. If homocysteine falls but symptoms persist, the explanation probably lies somewhere other than methylation. If it does not fall at all despite adequate form and dose, the assumption about which node was binding is probably wrong.
Intracellular status completes the picture where serum is insufficient, and genotype explains why a given form works better for one person than another.
It gives no doses. The right dose depends on genotype, baseline status, diet, medication and concurrent conditions, and cannot be generalised in an article.
It describes no composition. Which nodes should be supported simultaneously in an individual patient is a clinical judgement, and that judgement follows measurement.
And it does not claim that form selection alone determines the outcome. Form solves the conversion step. If the problem lies in reducing capacity, in load, or in an entirely different system, no form in the world will help.
Which form of folate should I take?
5-MTHF (methylfolate) is the form the cell uses directly and bypasses the MTHFR step. That is particularly relevant with an MTHFR variant, where conversion of synthetic folic acid is slow and incomplete. But active folate is not automatically right for everyone: without a variant there is no bottleneck to bypass, and high doses can then drive methylation faster than downstream capacity allows.
Which form of B6 and B12 is correct?
B6 should be given as P5P, pyridoxal-5-phosphate, because that is the form the enzyme uses — pyridoxine HCl must first be phosphorylated, a step that can be impaired. B12 occurs as cyano-, hydroxo-, methyl- and adenosylcobalamin, and the forms differ in stability, half-life and how they enter cellular cobalamin metabolism. Which is appropriate is determined individually.
Why did my supplement stop working after a while?
It probably did not — the bottleneck moved. When the most limiting step is corrected, flux rises until the next step becomes limiting. Partial compensation therefore often produces an initial improvement that plateaus. Full compensation means every node needing support receives it simultaneously, in a form it can use.
Is a good multivitamin enough?
Rarely, for two reasons. It often contains inactive forms that assume the conversion steps work, and it doses to an average rather than to what limits you specifically. It may also supply plenty of what you do not need.
How do I know whether compensation is working?
Measure homocysteine before starting and after eight to twelve weeks. It is a blunt but inexpensive readout of whether flux has improved. If it does not fall at all despite adequate form and dose, the assumption about which node was binding is probably wrong.
Which form and which node is relevant for you is determined by genotype and intracellular status. That is a measurement, not a guess.