Let me be clear about what I am and am not arguing here.
I am not arguing that folate is unimportant in pregnancy. The evidence that adequate folate in the periconceptional period reduces neural tube defects is robust and has been for decades. Neural tube defects are serious. Preventing them matters.
I am arguing that the delivery mechanism chosen — adding synthetic folic acid to a staple food consumed by the entire population, regardless of age, sex, pregnancy status, or genetic capacity to process it — is not the same thing as addressing folate insufficiency in the people who most need it. And that the distinction between these two things has significant clinical consequences that are not adequately acknowledged in the public health framing of this policy.
The stated goal is to prevent approximately 200 neural tube defects per year. The actual mechanism is to give synthetic folic acid daily to approximately 67 million people, most of whom are not pregnant, not planning pregnancy. Some of them carry common gene variants that slow one step of the folate cycle.
That is a one-size-fits-all intervention being applied to the most genetically and biochemically individual nutrient pathway in human metabolism. It is the opposite of test, don't guess.
Folic acid is not folate
This distinction is fundamental and consistently muddled in public health communications. Folate is the naturally occurring form — found in leafy greens, legumes, liver, and eggs — and enters the body as a variety of polyglutamate forms that are processed by gut enzymes into the monoglutamate form for absorption, then converted to 5-methyltetrahydrofolate (5-MTHF), the biologically active form your cells actually use.
Folic acid is a synthetic compound that does not exist in nature in this form. It requires reduction by the enzyme dihydrofolate reductase (DHFR) before it can enter the folate cycle. DHFR has limited capacity and is easily saturated. When intake of synthetic folic acid exceeds DHFR capacity — which is easily achieved with fortified flour consumed across multiple food sources daily — unmetabolised folic acid (UMFA) accumulates in the bloodstream.
The MTHFR dimension
MTHFR (methylenetetrahydrofolate reductase) is the enzyme responsible for the final conversion step — from 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate (5-MTHF), the active form that enters the methylation cycle. Two common single nucleotide polymorphisms — C677T and A1298C — reduce enzyme activity significantly.
The C677T homozygous variant reduces MTHFR activity by approximately 70%. The heterozygous variant reduces it by around 35%. These are not rare edge-case mutations. Population studies suggest C677T heterozygosity affects approximately 40% of many European populations, with homozygosity in around 10–15%. A1298C heterozygosity is present in a similar range. Note what MTHFR does and doesn’t do: it acts on folate from food as well as folate made from folic acid, after the DHFR step, so a variant slows the folate cycle whatever the source. The step that is specific to folic acid is DHFR, which is slow and varies a lot between people in human liver (Bailey & Ayling 2009).
Higher folic acid intake can increase circulating UMFA — which has been documented in American and Canadian populations following their earlier mandatory fortification programmes — while serum folate levels appear normal or elevated on standard testing, falsely reassuring both patient and clinician.
"Serum folate can look adequate or elevated while functional folate availability is impaired. The standard test and the clinical reality are telling completely different stories."
The B12 masking problem
This is the most clinically dangerous dimension of the folic acid story and the one with the longest documented history. High folate intake — including from synthetic folic acid — can normalise the macrocytic anaemia that is the visible marker of B12 deficiency, while the neurological damage from B12 deficiency continues unchecked.
The megaloblastic anaemia of B12 deficiency and folate deficiency are clinically indistinguishable on a standard blood count. The standard approach is to treat both, or test to distinguish them. But when synthetic folic acid is present in the food supply at significant levels, the haematological picture normalises and the B12 deficiency becomes invisible — until the neurological symptoms are advanced.
In older adults, in whom B12 absorption declines with age (often compounded by proton pump inhibitor use, metformin, or simple gastric atrophy), this masking effect is not theoretical. It is a documented clinical consequence of high-folate environments. My father is 82, on omeprazole, with a B12 of 361 and a rising MCV. The last thing he needs is additional synthetic folic acid in every slice of bread masking the picture further.
What functional testing actually shows
The limitations of standard serum folate and B12 testing in the context of fortification are precisely why functional markers matter. These are the tests that tell you what is actually happening inside the cell rather than what is circulating in the blood.
| Marker |
Test |
What it reveals |
Why fortification complicates it |
| FIGLU (marker 59) |
Mosaic OAT |
Functional intracellular folate status. Elevated when folate cannot be utilised for histidine metabolism — even when serum folate appears normal. |
Serum folate elevated by fortified food can mask FIGLU elevation. Client looks folate-replete on standard test while FIGLU confirms functional insufficiency. |
| Methylmalonic acid (MMA) |
OAT / blood |
Functional B12 status — most sensitive functional marker available. Elevated when B12 is insufficient at the cellular level regardless of serum B12. |
High folic acid intake masks the haematological signs of B12 deficiency. MMA is the more useful marker once the blood picture has been normalised by folate. |
| Homocysteine |
Blood chemistry |
Methylation efficiency. Elevated when either folate or B12 is insufficient for the methylation cycle — sensitive marker of functional deficiency in both. |
In MTHFR variants on high synthetic folic acid, homocysteine can remain elevated despite apparently adequate folate, revealing the conversion failure. |
| 2-OH:4-OH oestrogen ratio |
DUTCH Plus |
Oestrogen clearance pathway. The 4-OH pathway is methylation-dependent — impaired methylation diverts oestrogen toward the potentially genotoxic 4-OH pathway. |
MTHFR-impaired methylation reduces COMT activity, impairs 4-OH oestrogen methylation, and elevates genotoxic oestrogen metabolites. Directly relevant to oestrogen-driven conditions and cancer risk. |
| Serum B12 |
Blood chemistry |
Circulating B12 — useful screening but not functional. |
Can appear normal with elevated MMA. In fortification environments, B12 deficiency may be masked haematologically. If serum B12 comes back borderline, ask about an MMA or homocysteine test. |
| 5-HIAA / HVA |
OAT |
Serotonin and dopamine metabolites. Both neurotransmitter pathways are methylation-dependent. |
A proposed link: impaired methylation could affect neurotransmitter metabolism. Mechanistic and untested as a cause of symptoms in people with MTHFR variants; no study has shown UMFA does this. |
The informed consent question
The policy will apply to all non-wholemeal wheat flour — including organic. There is no opt-out. There is no labelling requirement that clearly distinguishes fortified from unfortified flour. There is no mechanism by which a person with a confirmed MTHFR variant, or a clinician managing a patient with B12 deficiency, can reliably ensure that the staple foods in their diet do not contain synthetic folic acid.
The government's position, and that of bodies like the British Dietetic Association, is that the dose is small, the benefit to NTD prevention is clear, and the risks are manageable. This may be true at the population level for the specific outcome they are measuring — neural tube defect incidence. It does not address the question of what a 70-year daily exposure to synthetic folic acid does to the methylation capacity of a person with C677T homozygosity, or to the B12 picture of an 82-year-old on omeprazole.
The principle that a public health intervention must benefit the population it targets without causing disproportionate harm to identifiable subgroups who cannot be given a choice — that principle is not being adequately applied here. Unmetabolised folic acid is one of the open questions, and whether it does any harm has not been shown either way.
"This is a one-size-fits-all intervention applied to the most genetically individual nutrient pathway in human metabolism. It is the opposite of personalised medicine. It is the opposite of test, don't guess."
A better approach exists
The argument is not against folate. It is against the delivery mechanism. One alternative is 5-methyltetrahydrofolate (5-MTHF, methylfolate). Because it isn’t folic acid, it can’t add to UMFA. This is the active form. It does not require DHFR or MTHFR conversion. It is bioavailable to MTHFR variant carriers and non-carriers alike. It does not accumulate as UMFA.
Targeted supplementation programmes for women planning pregnancy — with methylfolate rather than synthetic folic acid — would avoid exposing the rest of the population. Their weakness is reach: they only work for women who plan ahead and take a supplement early enough, which is the reason most countries chose fortification. On the other side, mandatory fortification has the stronger record: across 14 studies covering more than 33 million people it was linked to 44% fewer neural tube defects (Moges 2026), and in the US it raised folate and lowered homocysteine (Jacques 1999).
That approach requires individualisation. It requires education. It requires that the health system trusts people to act on information rather than administering nutrients through the food supply without their knowledge. It is, by every measure of personalised medicine, superior. It is also, clearly, harder to implement than adding a powder to a milling process.
What you can do now
If you are concerned about your own methylation status, MTHFR variant status, or B12/folate functional picture, the following is the relevant clinical picture:
- A standard serum folate and B12 will tell you your circulating levels — not your functional status
- The Mosaic OAT includes FIGLU (marker 59) — the functional intracellular folate marker — alongside MMA and the full methylation picture
- A comprehensive blood chemistry panel with homocysteine gives the methylation efficiency marker most directly
- DUTCH Plus includes the oestrogen metabolite ratios that reveal methylation's downstream effects on hormone clearance
- If you carry a confirmed MTHFR variant, supplement with methylfolate (5-MTHF) rather than folic acid — and avoid fortified foods where possible once the policy takes effect
If your serum folate is elevated or high-normal while your homocysteine is also elevated, this is a red flag for MTHFR-impaired conversion — the standard interpretation ("good folate levels") is misleading.
The flour will be fortified. That appears to be settled. What is not settled is whether clinicians, practitioners, and informed individuals allow this to pass without demanding the monitoring infrastructure to detect harm in the populations most vulnerable to it — adequate B12 surveillance in the elderly, FIGLU and MMA testing for MTHFR-confirmed individuals, and genuine transparency about UMFA accumulation in the UK population over time.
Test, don't guess applies here as much as it applies to any other clinical situation. The dose makes the poison. The variant determines the dose. One size does not fit all — and in methylation, that statement is more literally true than almost anywhere else in human biochemistry.