Post 05

The Supplement Most People Take Wrong

William Kasel·1 min read

MTHFR + folic acid. 40% of people have this variant.

~40% of people have a genetic variant that makes folic acid significantly less effective — and they have no idea.

It's called MTHFR. Your doctor probably hasn't tested for it.

Here's what you need to know. 🧵

Your body needs folate (vitamin B9) for:

Most supplements and fortified foods use FOLIC ACID - the synthetic form.

To use folic acid, your body must convert it using the MTHFR enzyme.

If you have the common variant (C677T or A1298C):

That unprocessed folic acid can actually BLOCK the receptors that real folate needs.

I have compound heterozygous MTHFR (one copy of each variant).

For years I took a standard multivitamin with folic acid. It wasn't helping. It may have been making things worse.

Switched to methylfolate (the pre-converted form) and the difference was noticeable within weeks.

How to know if this affects you:

Get MTHFR tested (23andMe raw data has it, or ask your doctor)
Check your supplements - does the label say "folic acid" or "methylfolate" (5-MTHF)?
If you're pregnant or planning: this is CRITICAL. Talk to your OB about methylfolate vs folic acid.

This isn't fringe science. MTHFR is one of the most studied genetic variants in medicine.

40% of people have at least one copy. It takes 30 seconds to check your supplement label.

Swap folic acid → methylfolate. That's it.

Might be the highest-ROI health change you make this year.

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