Right to Adequate Folate Levels

“Folate, an essential nutrient integral to the function of numerous critical cellular processes, functions as a family of metabolic cofactors that participate in 1-carbon transfer reactions, cellular methylation reactions, amino acid metabolism, and nucleotide biosynthesis. […] There are concerns of potential adverse effects of excess folic acid intake and/or elevated folate status. Observations indicating adverse effects from excess folic acid intake, elevated folate status, and unmetabolized folic acid (UMFA) remain inconclusive; the data do not provide the evidence needed to affect public health recommendations. However, the body of evidence on potential adverse health outcomes indicates the need for comprehensive research to clarify these issues and bridge knowledge gaps.” — Maruvada, Stover, Mason et al. — NIH Workshop, American Journal of Clinical Nutrition, 2020¹²

This passage does not come from a fringe working group: it brings together experts from the NIH, the FDA, the CDC, Canadian and American universities, and three of the leading researchers in folate metabolism — Patrick Stover, Joel Mason, Jacob Selhub. Its scope is precise: the scientific institutions that declared victory over folate deficiency through fortification acknowledged, in 2020, that they do not know the effects of their own policy on cellular biochemistry. This report documents why that ignorance is not trivial.

A century of warnings

In 1931, Dr Lucy Wills (1888–1964) identified a severe anaemia in pregnant mill workers in Bombay, curable with brewer’s yeast³⁴. She isolated what she called the “Wills factor” — renamed folic acid in 1941 after its extraction from spinach leaves⁵. In 1945, synthetic folic acid was recognized as a treatment for megaloblastic anaemia. In 1991, a randomized trial by the British Medical Research Council showed that supplementation reduced the risk of neural tube defects (NTD) by 72%⁶. The evidence was irrefutable. Policy, however, lagged.

Since 1991, more than 5 million pregnancies affected by neural tube anomalies could have been prevented by universal fortification⁷⁸. Mandatory fortification — adopted in Canada and the United States in 1998, now deployed in approximately 80 countries⁹ — represents a real but partial success. It reduced NTDs by 46% in Canada and by 19 to 31% in the United States¹⁰¹¹, but neural tube defects represent only a fraction of conditions linked to folate status. Spina bifida is the visible and quantifiable symptom of a far broader problem — and it is precisely this visibility that led to reducing folate to an obstetric matter, at the expense of its systemic implications.

In 2024, an analysis published in The Lancet Global Health estimated that more than 4 billion people have insufficient folate worldwide¹². In fortified countries, plasma markers appear normal — but functional markers tell a different story.

Two worlds, one shared ignorance

Countries without fortification: classical, invisible deficiency

In non-fortified or incompletely fortified countries — the majority of the planet — folate deficiency remains massive and silent. Initial symptoms (fatigue, irritability, concentration difficulties) are non-specific and attributed to other causes. Megaloblastic anaemia, a late stage of deficiency, is diagnosed when tissue stores have already been depleted for months¹³. Women of childbearing age are the most exposed — but they are not the only ones.

Subclinical insufficiency — plasma levels “within the normal range” but biologically insufficient to sustain optimal metabolism — affects a considerable proportion of the world’s population. Cohort studies show that serum levels classified as “low-normal” (≥ 1.5 and ≤ 5.9 ng/mL, within official reference limits) are associated with a 1.3-fold higher risk of cognitive disorders in the elderly, and that a decline toward this low-normal range over 4 years multiplies the incident risk of dementia by 2.4¹⁴¹⁵. Deficiency is not binary. It is a continuum, and most of it occurs in the invisible zone between “sufficient” and “optimal.”

Countries with fortification: the false victory

In fortified countries — Canada and the United States foremost — plasma folate levels rose significantly after 1998. The prevalence of megaloblastic anaemia fell. NTDs receded. Institutions declared victory. And vigilance relaxed.

Yet an NHANES analysis conducted 20 years after the introduction of fortification in the United States shows that plasma folate concentration began a moderate decline after 1999–2004, and that insufficiency persists at approximately 20% of the population depending on the thresholds used¹⁶. In Canada, data from the Canadian Health Measures Survey (~5,600 participants, 2007–2009) reveal that while “classic” folate deficiency is nearly absent, 4.6% of Canadians are deficient in B12, and in at-risk genetic populations (carriers of the MTHFR C677TT variant), homocysteine remains significantly elevated despite a fortified environment¹⁷¹⁸. The illusion of complete coverage rests on a marker (serum folate) that provides no information about the biological efficiency of the methyl cycle.

More troubling still: among Canadian children with sickle cell disease supplemented with 1 mg/day of folic acid according to standard protocols, a study showed that UMFA (unmetabolized folic acid) was detectable in all children¹⁹. Food fortification, combined with pharmaceutical supplementation, places these children in a regime of chronic exposure to a compound whose biological effects are, in the NIH’s own words, unknown¹.

The testing trap

A marker that does not measure what we think it measures

Serum folate measures instantaneous plasma concentration — it can be normalized by a single meal rich in green vegetables and fluctuates over days¹³²⁰. It is an indicator of recent intake, not of tissue stores or the functional efficiency of the methyl cycle.

Erythrocyte folate (in red blood cells) reflects average status over the preceding 2–3 months, analogous to HbA1c for glucose — it is a far more stable marker²¹²². Studies show that approximately 5% of people with normal serum folate have deficiency confirmed by the red blood cell test¹³.

But the most neglected diagnostic tool remains the measurement of plasma homocysteine. Homocysteine is an intermediate product whose accumulation directly signals a failure of the methyl cycle — whatever the defective link (folate, B12, B6, MTHFR)²³²⁴. In routine clinical practice, this measurement is only ordered at the explicit request of a physician, and it does not appear in standard blood panels²³. Yet longitudinal studies on high-functioning adults show that individuals in the lowest quartile of folate have a 1.6-fold higher risk of cognitive decline over 7 years — independently of homocysteine, suggesting a direct effect of folate on the brain, beyond the homocysteine proxy alone²⁵²⁶.

The official surveillance system speaks in terms of “serum folate” and declares victory when anaemic deficiency disappears. It does not speak of methyl flux, SAM/SAH ratio, 5-MTHF bioavailability, or DHFR saturation. This is not a technical detail — it is the difference between measuring tyre pressure and measuring tread wear.

The methyl cycle: architecture of cellular life

Far more than a “pregnancy vitamin”

Reducing folate to the “pregnancy vitamin” is perhaps the greatest distortion in twentieth-century nutritional literature. Folate is the cornerstone of one-carbon metabolism (OCM) — the metabolic network on which simultaneously depend:

• DNA and RNA synthesis (three of the four nucleotides required for DNA biosynthesis require a one-carbon unit carried by folate)²⁷²⁸
• DNA methylation (epigenetic regulation of gene expression)²⁹³⁰
• Histone methylation (chromatin structure)²⁹
• Neurotransmitter synthesis (serotonin, dopamine, noradrenaline, melatonin)²⁴³¹
• Hepatic lipid metabolism (phosphatidylcholine, VLDL, steatosis)³²³³
• Antioxidant defence (glutathione)²⁸³⁴

At the centre of these processes is the production of S-adenosylmethionine (SAM), the universal methyl donor. SAM is synthesised from methionine via the methyl cycle; its regeneration depends on active folate (5-MTHF) and vitamin B12 for the remethylation of homocysteine to methionine. Every cellular methylation reaction — there are hundreds — converts SAM into S-adenosylhomocysteine (SAH). The SAM/SAH ratio is the barometer of the cell’s methylating potential: when it falls, the entire epigenetic, neurochemical, and hepatic programme degrades²⁹³⁵.

The liver: factory and victim of the methyl cycle

The liver is the central organ of the methyl cycle. It stores 50% of the body’s total folate, mainly as 5-MTHF, and concentrates all the enzymes of the cycle²⁸. When the methyl cycle is disrupted — by folate deficiency, an MTHFR variant, or paradoxically by an excess of synthetic folic acid — it is the liver that pays the first price.

Mouse studies show that folate deficiency, combined with the MTHFR C677TT variant, reduces the SAM/SAH ratio, lowers methyltetrahydrofolate and betaine levels, raises homocysteine, and causes hepatic fibrosis in males and steatosis in females — with a sexual dimorphism revealing the complexity of genotype–nutrient interactions³⁶. In murine models of high-fat feeding, dysregulation of the hepatic methyl cycle is accompanied by a 30% depletion of methionine, elevated SAH, and hepatic fat accumulation³⁷. These mechanisms are now documented in humans: metabolomics data in NAFLD (non-alcoholic fatty liver disease) show the same methyl cycle failure signatures³⁸.

NAFLD affects approximately 25% of the world’s population³³. A significant fraction of its pathogenic mechanisms passes through one-carbon metabolism dysregulation — and this connection is absent from standard clinical guidelines on NAFLD management.

The undermethylated brain

Brain chemistry that depends on the methyl cycle

Normal brain function — not just disease — depends on a continuous flux of methyl groups. SAM is indispensable for DNA and histone methylation in neurons, for the synthesis of myelin phospholipids (phosphatidylcholine), and for the methylation of monoamine neurotransmitters³¹³⁹. The pathway is precise: 5-MTHF crosses the blood-brain barrier, remethylates homocysteine to methionine, generates cerebral SAM, which fuels the production of tetrahydrobiopterin (BH4) — an essential cofactor for the enzymes that synthesise dopamine (tyrosine hydroxylase) and serotonin (tryptophan hydroxylase)^24404142.

Without sufficient 5-MTHF:

• BH4 production is compromised
• Synthesis of dopamine, serotonin, noradrenaline, and melatonin falls
• Cerebral SAM decreases, impairing methylation of neuronal histones and DNA
• Homocysteine accumulates and exerts direct neurotoxicity (NMDA receptor activation, oxidative stress, cerebrovascular lesions)²⁴⁴³

This is not a rare disease. It is the daily functioning of the brain. Concentration, working memory, emotional regulation, sleep quality (melatonin), cognitive processing speed — all these processes have a direct metabolic dependence on methyl flux⁴⁴³⁹.

“Normal” is already compromised

Data from 3,910 elderly participants with folate within the normal range show that the group in the lowest quartile (still within reference values) has a 1.3-fold higher risk of cognitive impairment than the highest quartile group, and that a decline toward this low-normal range multiplies the incident risk of dementia by 2.4 over 4 years of follow-up¹⁴¹⁵. This is not deficiency in the clinical sense. This is a gradient within the “normal” zone. Medicine has drawn its thresholds to detect acute pathological states — not to optimize brain biochemistry.

Data from the MacArthur Studies of Successful Aging (499 high-functioning adults aged 70–79) confirm that the lowest quartile of folate is associated with a 1.6-fold higher risk of cognitive decline over 7 years, independently of homocysteine — suggesting a direct effect, beyond simple homocysteine toxicity²⁵⁴⁵. A study in patients with cognitive decline and folate deficiency shows that folate supplementation reduces plasma homocysteine and improves MMSE (cognitive score) regardless of the extent of hippocampal atrophy⁴⁶. The question is not merely “is my B9 within the normal range?” — it is “is my methyl cycle running fast enough to sustain continuous brain methylation?”

Inventory of conditions linked to functional deficiency

Cancer: defective epigenetics

Folate is indispensable to DNA methylation via SAM. Without sufficient methyl flux, normally silenced genes (proto-oncogenes) can activate through local hypomethylation, while tumour suppressor genes deactivate⁴⁷⁴⁸. The mechanism is precise: folate deficiency reduces the SAM/SAH ratio in the nascent cancer cell, induces hypomethylation at the promoter of proto-oncogenes such as FOS, and activates oncogenic effectors CCND1, BCL2, and PLAU⁴⁸. At the other extreme, uracil inserts in place of thymine in DNA when folate is lacking, causing double-strand breaks — the soil of genomic instability⁴⁹⁵⁰.

In December 2025, a team at Weill Cornell Medicine published that folate deficiency induces characteristic genetic changes found in lung tumours. Dr Guillermo Burgos Barragan stated:

“Researchers have known about these genetic changes for many years, but no one knew what caused them. Our data suggests that folate deficiency is a major contributor to lung cancer development and progression.”⁵¹

Unmetabolized folic acid: an example of institutionalised incompetence

The pro-vitamin that invades bodies

Synthetic folic acid — present in enriched flours, cereals, supplements, and multivitamins — is not folate. It is an oxidised pro-vitamin, with no intrinsic biological activity, that must be reduced by two successive enzymes (DHFR, then MTHFR) before it becomes usable⁵²⁵³. But human DHFR is a low-capacity enzyme, which saturates beyond ~200 µg of ingested folic acid⁵⁴¹. Beyond this threshold, folic acid accumulates in the blood in its unconverted form: UMFA (Unmetabolized Folic Acid).

The consequence has been documented since the 2000s — and is almost universally ignored by clinical practice:

• In US NHANES data, UMFA is detectable fasting in 38% of the population aged over 60, with a mean of 4.4 ± 0.6 nmol/L⁵⁵
• More sensitive methods (HPLC–MS) reveal detectable UMFA in more than 95% of serum samples from the US population, regardless of reported intake¹
• In Canada, among children with sickle cell disease supplemented at the standard dose of 1 mg/day, UMFA is detectable in 100% of cases¹⁹
• In Ireland, 95% of elderly individuals had detectable UMFA even in the absence of mandatory fortification — indicating that voluntary cereal fortification is sufficient to saturate DHFR¹

UMFA inhibits what it was meant to replace

A clinical paradox documented by Christensen et al. in the American Journal of Clinical Nutrition (2015): high folic acid consumption inhibits MTHFR activity in the laboratory and reduces MTHFR protein in the livers of mice fed for 6 months, creating a pseudo-MTHFR deficiency⁵⁶⁵⁷. The consequences: reduced hepatic 5-MTHF, a drop in the SAM/SAH ratio, reduced phosphatidylcholine levels, and histological liver lesions — particularly in individuals already carrying the Mthfr +/− variant⁵⁶⁵⁸.

Simply put: giving excess folic acid to someone with reduced MTHFR can worsen the functional deficiency in active folate. Unconverted folic acid occupies enzyme sites, blocks the entry of natural 5-MTHF, and produces the opposite of the intended effect. Alnabbat et al. (2022) titled their paper: “Excessive Folic Acid Mimics Folate Deficiency in Human Lymphocytes” — the markers of genomic instability, altered methylation, and oxidative stress are identical between deficiency and excess⁵⁹⁵⁰.

UMFA masks B12 deficiency — and worsens the neurological prognosis

The interaction between UMFA and B12 is perhaps the most clinically serious consequence of fortification policy, and one of the least known. Folic acid corrects megaloblastic anaemia — the visible haematological sign of B12 deficiency. But the neurological lesion of B12 deficiency (demyelination, spinal cord damage, cognitive impairment) continues to progress even when the anaemia is masked^54606162.

The study by Selhub et al. in PNAS (2007), based on NHANES data, quantifies this paradox: in subjects with low B12 (< 148 pmol/L), elevated serum folate is associated with a paradoxical elevation of both homocysteine AND methylmalonic acid — two markers of functional B12 failure. In other words, in people deficient in B12, excess folate worsens the functional indicators of B12 deficiency rather than correcting them⁶³⁶⁴. These same subjects show a higher prevalence of anaemia and cognitive impairment compared to subjects with low B12 and normal folate⁶³.

The immune cost

Studies in postmenopausal women show that the presence of UMFA in plasma is associated with approximately 23% reduced NK (natural killer) cell cytotoxicity⁶⁵. A study in elderly mice fed excess folic acid confirms the causal relationship: less efficient NK cells, reduced capacity to destroy infected or tumour cells⁶⁶. A dose of 5 mg of folic acid per day for 90 days in humans is associated with increased UMFA and reduced NK cytotoxicity⁶⁷⁶⁸.

NK cells constitute a first line of defence against viruses and oncogenically dysregulated cells. Their functional decline is not trivial in an elderly population — precisely the one that accumulates the most UMFA and faces the highest B12 and oncological risks.

Fortification as alibi

What was solved — and what the solution allowed to be ignored

Mandatory fortification accomplished something real and quantifiable: a 46% reduction in NTDs in Canada¹⁰ and an accelerated fall in stroke mortality in the years following 1998 in the United States and Canada, not observed in England (without fortification), and attributed in part to a reduction in homocysteine⁶⁹. These are lives saved, suffering prevented.

But fortification also served as a shield. It allowed institutions to declare that “the folate problem is solved” — and to stop questioning:

• the distinction between natural dietary folate (reduced polyglutamates, directly bioactive) and synthetic folic acid (oxidised pro-vitamin, requiring activation)
• the functional status of the methyl cycle (SAM/SAH ratio, homocysteine, cerebral 5-MTHF)
• individual variability related to MTHFR variants (25% of the world population in TT or CT genotype⁷⁰) for whom synthetic folic acid is partially unusable
• chronic saturation of DHFR by fortification combined with supplementation, creating a near-universal UMFA regime

Worse still: UMFA binds to folate receptors (FOLR) with 6 to 10 times greater affinity than 5-MTHF¹. This means synthetic folic acid competes with the active form for access to the cerebral, placental, and renal transporter — without necessarily being converted once inside. The receptor is occupied by a purported nutrient that is biologically inert¹.

Fortification made synthetic folic acid the de facto universal standard for folate supplementation — while the only biologically active form, 5-MTHF, is available and directly usable. This choice is not justified by physiology. It is justified by history (folic acid was the compound synthesizable in 1945), economics (cheaper), and a regulatory inertia that conflates “improved blood levels” with “normalized cellular biochemistry.”

What the experts say — in their own words

Prof Nicholas J. Wald — The silent tragedy

Professor of preventive medicine at Queen Mary University of London, author of some of the most direct calls on global inaction. In Public Health Reviews (2018)⁷⁸:

“Failure to fortify is more than a missed opportunity; it is a tragedy. Since 1991, it has been estimated that there have been over five million preventable NTD pregnancies in the world. While the thalidomide tragedy prompted immediate worldwide public health intervention, many countries still ignore the preventable toll of disability, stillbirth, infant death, and terminations of pregnancy caused by NTDs.”

Wald identifies spina bifida as visible and preventable. This documentation broadens the frame: the 5 million NTDs are merely the visible tip of a systemic failure of the methyl cycle on a planetary scale.

Prof Patrick J. Stover — The ignored complexity

Professor of biochemistry at Florida State University, former director of the Cornell nutrition programme, member of the National Academy of Sciences. Co-author of the NIH report on effects of excess folate/folic acid, American Journal of Clinical Nutrition, 2020¹²:

“Impairments in folate-mediated 1-carbon metabolism are associated with several common diseases and developmental anomalies including intestinal cancers, vascular disease, cognitive decline, and neural tube defects. Folate and other B-vitamins fundamentally differ from other nutrients that interact with the genome in determining health and disease outcomes in that their interaction is reciprocal.”⁷¹

And in the same 2020 NIH article, the team explicitly acknowledges that UMFA is present in more than 95% of sera from the US population by sensitive methods, and that “health is not known” for these levels of chronic circulation¹.

Dr Aron Troen — The immune alarm

Researcher at the Jean Mayer USDA Human Nutrition Research Center on Aging (Tufts University), author of the pivotal study on UMFA and NK cells in healthy women. In Journal of Nutrition (2006)⁶⁵:

“We found an inverse relation between the presence of unmetabolized FA in plasma and NK cytotoxicity. NK cytotoxicity was approximately 23% lower among women with UMFA in plasma than among women without it.”

This study was published 20 years ago. It remains ignored by virtually all clinical guidelines on folic acid supplementation.

Karen Christensen & Rima Rozen — The pseudo-deficiency created by excess

The team of Rima Rozen at McGill University (Montreal), pioneers in the study of the human MTHFR variant, showed in 2015 that high folic acid consumption creates a pseudo-MTHFR deficiency with liver lesions⁵⁶. Conclusion of the paper:

“We suggest that high folic acid consumption reduces MTHFR protein and activity levels, creating a pseudo-MTHFR deficiency. This deficiency results in hepatocyte degeneration, suggesting a 2-hit mechanism whereby mutant hepatocytes cannot accommodate the lipid disturbances and altered membrane integrity arising from changes in phospholipid/lipid metabolism. These preliminary findings may have clinical implications for individuals consuming high-dose folic acid supplements, particularly those who are MTHFR deficient.”⁵⁷

This work was carried out in Montreal, in a Canadian institution, in a country where fortification has been mandatory since 1998. It did not modify Canadian public health recommendations.

Dr Jill James — Maternal epigenetics and autism

Biochemist at the Metabolic Genomics Laboratory (Arkansas Children’s Hospital), Jill James demonstrated that polymorphisms in the RFC-1 gene (folate transporter) in mothers of autistic children are associated with global DNA hypomethylation in the mother — a profile of functional active-folate deficiency visible despite apparently normal dietary intake⁷²⁷³. In American Journal of Medical Genetics B:

“Maternal genetic variants that compromise intrauterine availability of folate derivatives could alter fetal cell trajectories and disrupt normal neurodevelopment.”⁷²

Timeline: from discovery to the illusion of resolution

References