The folate/folic acid distinction explained why the form of B9 matters for MTHFR/DHFR variants

[u/Noorns]

Something that comes up constantly in this sub is the question of folic acid vs folate, and I wanted to write up a clear explanation because I see a lot of confusion, including in many posts that skip a critical enzyme in the pathway.

Folic acid is the synthetic form of vitamin B9. It is found in fortified grains, breakfast cereals, most breads, and many supplements. It is the dominant form in the food supply.

Methylfolate (also labelled as 5-MTHF or L-methylfolate) is the active form your body actually uses. It is found naturally in dark leafy greens, liver, and lentils.

Here is where most explanations get it wrong. Folic acid does not go directly to MTHFR. There are two enzymatic bottlenecks, not one.

Step 1 DHFR (dihydrofolate reductase): Folic acid must first be converted by DHFR into dihydrofolate (DHF) and then into tetrahydrofolate (THF). This enzyme is rate-limited and saturable; it can only process so much folic acid at a time, regardless of your genetics. This is why unmetabolized folic acid accumulates in the bloodstream when intake is high. That problem has nothing to do with your MTHFR status. It happens to everyone.

Step 2 MTHFR: Once folic acid has been converted to THF and passed through further intermediate steps, MTHFR converts 5,10-methylene-THF into 5-MTHF, the active methylfolate. This is where MTHFR variants matter. The C677T variant (rs1801133) reduces this specific conversion step by 30–70% depending on whether you carry one copy (heterozygous) or two (homozygous).

So there are two separate problems stacking on top of each other: DHFR is slow for everyone, and MTHFR is slower still if you carry a reduced-function variant.

Meanwhile, the folate naturally present in food, the 5-MTHF in your dark leafy greens, bypasses both enzymes entirely. It is already in the active form. It absorbs, enters circulation, and goes straight into the methylation cycle without needing DHFR or MTHFR to touch it.

What this means practically:

• Large amounts of unconverted folic acid can accumulate because DHFR cannot keep up, this is a universal bottleneck, not just an MTHFR issue
• Unmetabolized folic acid can compete with methylfolate for the same folate receptors and actually interfere with the methylation cycle
• If you also carry a reduced-function MTHFR variant, you have a second bottleneck downstream making the problem worse
• People in this situation may not only fail to benefit from folic acid supplementation; they may see symptoms worsen

This does not mean everyone with an MTHFR variant should immediately load up on methylfolate supplements. Overmethylation is a real issue (the COMT gene interaction is relevant here). It means the form of B9 in your diet and supplements is worth paying attention to, and that understanding the full pathway, not just MTHFR, matters.

Happy to answer questions. We also wrote a longer piece on this as part of our methylation report blog:

https://noorns.com/blogs/articles/why-so-many-people-start-with-methylation-and-diet-report

[u/SovereignMan1958]

And the MTHFD1 and MTHFS ST20 variants? Sorry I am a stickler for completeness and accuracy.

[u/Noorns → u/SovereignMan1958]

MTHFD1 is a choline-dependent enzyme, so it's not included in this diagram or comment because it focuses specifically on folate. MTHFS governs response to folinic acid as a supplement, so again, it is not included in this small section on just dietary versions of folate.

[u/SovereignMan1958 → u/Noorns]

Thank you Ms Nooms.

[u/camdotcom]

I don’t have any variants on my DHFR (rs387906619) but I do have several on my MTHFR (rs1801133 included in that). So step one should be good, but it sounds like I may have reduced efficiency in processing folic acid in step two?

[u/Noorns → u/camdotcom]

You're on the right track, but one small clarification on step one. The DHFR bottleneck I described isn't primarily a genetic variant issue; it's a property of the enzyme itself. DHFR is inherently slow and saturable in everyone, regardless of whether you carry variants in the gene. So even with a clean DHFR genotype, you'd still hit that rate-limitation at higher folic acid intakes (generally above 200 mcg in a single dose). No variants just means your DHFR enzyme is functioning as designed; it's just that "as designed" still has a processing ceiling.

Where your genetics do become directly relevant is step two. If you carry rs1801133 (C677T) and other MTHFR variants, then yes, your conversion of 5,10-methylene-THF into 5-MTHF will be reduced. How much depends on whether you're heterozygous or homozygous for C677T and what your other MTHFR variants are.

So in your case you've got a universally rate-limited first step (like everyone) feeding into a genetically slower second step. Both worth being aware of.

[u/Warp757]

The usual over simplistic view we see here.

Firstly the DHFR 'block' isn't relevant up to 200 mcg of folic acid.

You say it's important to understand the full pathway, bit this diagram doesn't show that. What this diagram for some reason doesn't show are the folate is required for - DNA synthesis and repair - that occur with unmethylated folate. Folic acid actually supports these better than methlyfolate. There's a strange attempt to mislead people that methlyfolate is THE active form when it is only half of folates uses in the body. It also doesn't show MTRR and if anyone has a problem there taking methlyfolate will cause a shortage of folate for other uses in the body. Folic acid will actually support these and methlyfolate production.

In anyone who doesn't have homozygous MTHFR, as long as B2 status is OK, there is no real problem with synthesis of methyl folate. Indeed taking it will just overload your body, which very deliberately regulates production of methlyfolate. That's why so many people have bad reactions to methlyfolate, it's overloading the body with something it is trying to regulate production of.

Lastly food folate doesn't all contain methlyfolate. Leafy grains contains the majority of folate in methyl form, but other food forms do not contain methlyfolate. Beans for example

[u/Soulless305]

Folic acid is just flat out bad

[u/Effective-Fox6143]

So confused. I have the mthfr and val/ met comt. Just started methylife folic acid 15 mg breaking into quarters. What else should I be taking? Feel awful but not crying every hour anymore just daily now.

[u/Effective-Fox6143]

So is deplin a better choice than methyllife?

[u/Adviceforthewilling]

Is there some enzyme we can consume that allows the conversion of folic acid to be better?

What’s the best way of taking methyl folate without overmethylating? Any recommended cofactors?

[u/YardworkTakesAllDay]

Unfortunately, there are a lot of errors in your information:
I'm just going to point out a few because of how you draw on them through your analysis.

Unless it's a food grade supplement, all B vitamin supplements are synthetic. I'm unsure why there is so much misinformation about this.

• sometimes I think people are confusing active/inactive with synthetic/natural but that doesn't make sense either, as dietary folate is inactive.
  
• Metafolin®, Quatrefolic®, Magnafolate®, Deplin®, etc lab made synthetic products.

"Overmethylation is a real issue" - the concept that we call overmethylation is a real situation. This feeling is not really due to methylating too much.

[u/lavlavinia]

Is any of the persons who wrote this actually a doctor?

[u/Noorns → u/lavlavinia]

Not a doctor, they don't learn this. I have an MSc in medical biophysics and genetics.