BRS2-1-1 - Folate/B12-Dependent Homocysteine Remethylation
(Recycling Homocysteine With Folate & B12)
1. Mission & Overview + Dietary Levers
Mission
Recycle homocysteine to methionine through folate and B12 so methyl-donor supply and homocysteine control stay supported.
Intervention Dominance: Diet-Dominant
-
Vitamin B2
-
5-Methyltetrahydrofolate
-
Vitamin B9 (folate)
-
Methylcobalamin
-
Vitamin B12 (cobalamin)
- Homocysteine
KC1’s independently admitted folate supply is disclosed under Vitamin B9 (folate) in the dietary requirements. Its full five-atom disclosure is retained there; a second identical disclosure is consolidated. Betaine and choline are not admitted as PM1 methyl-donor inputs. The stronger tissue-capacity constraint remains unresolved.
Overview
Methionine synthase transfers a methyl group from 5-methyltetrahydrofolate to homocysteine, forming methionine and tetrahydrofolate. [9] Methylcobalamin, the vitamin B12 cofactor, takes part in that transfer. [9] Regenerated methionine can later be used to form SAMe, in a separate reaction. [9] Folic acid and vitamin B12 can lower blood homocysteine. [1] That change is a circulating marker, not tissue remethylation flux. [1]
- Benefits: Remethylating homocysteine restores methionine, which can then be converted into SAMe. [9] This helps maintain the methyl-group supply used by later methylation.
- Implementation Notes: 5-Methyltetrahydrofolate, vitamin B9 (folate), methylcobalamin, and vitamin B12 (cobalamin) are the provision routes. [9] [1] Homocysteine is the substrate already in the pathway, not a dietary target. Lowering blood homocysteine does not set a dose for tissue remethylation flux. [1]
- Biological Relevance: Betaine-dependent remethylation and transsulfuration are neighbouring routes, not this reaction. [9]
2. Primary Biological Effects
↓ homocysteine; ↑ methionine regeneration
3. Intervention Levers
1. Food Preparation & Delivery ONLY
- Consistent daily meal timing may support one-carbon and methyl-donor availability across the day.
- Soak and cook thoroughly to reduce phytates and improve mineral bioavailability; soaking and spro… — see Lentils — Preparation.
- Pair fat-soluble compounds with dietary fat to support absorption — see Spinach — Synergies.
- Sleep and stress context may indirectly affect methylation demand; lifestyle factors are secondary to dietary substrate supply for this PM.
4. Mechanistic Basis
Summary
Maintaining a usable methionine supply depends on recycling homocysteine through the folate- and B12-dependent route. That reaction feeds methionine toward later SAMe formation, but it is not itself SAMe synthesis, betaine remethylation, or homocysteine disposal.
(Methionine synthase reaction)
Methionine synthase transfers a methyl group from 5-methyltetrahydrofolate (a reduced folate carrying one methyl group) to homocysteine. The products are methionine and tetrahydrofolate. The methyl group is carried by methylcobalamin, the active vitamin B12 cofactor on the enzyme [Froese et al. (2019) [9]].
Dietary folate, including folic acid after reduction by dihydrofolate reductase, can be converted to that 5-methyltetrahydrofolate substrate. Dietary vitamin B12 is absorbed and processed to methylcobalamin on the enzyme. Those are provision routes, not evidence that a higher intake speeds the reaction in tissues [Froese et al. (2019) [9]].
(Riboflavin sits beside the reaction)
Riboflavin is the precursor of flavin adenine dinucleotide. That flavin is a cofactor of methylenetetrahydrofolate reductase, the enzyme that makes 5-methyltetrahydrofolate, and of methionine synthase reductase, which repairs inactive cobalamin. It is not the cofactor in the synthase active site. That site uses methylcobalamin [García-Minguillán et al. (2014) [10]].
In adults, riboflavin status changed how an upstream reductase variant related to blood homocysteine. That interaction does not place riboflavin on methionine synthase itself [García-Minguillán et al. (2014) [10]].
(Blood homocysteine is not the reaction rate)
Folic acid lowers blood homocysteine, and vitamin B12 lowers it further. Vitamin B6, which serves a different disposal route, did not add a clear further reduction in the same pooled trials [Collaboration (1998) [1]]. Blood homocysteine is a circulating marker. A lower value does not measure how fast this reaction runs in a tissue.
(Boundaries of the mechanism)
This reaction is folate- and B12-dependent remethylation only.
The parallel betaine route, which also makes methionine but does not use 5-methyltetrahydrofolate or vitamin B12, belongs to BRS2-FM1-PM2 — Betaine/BHMT Remethylation. Conversion of methionine to SAMe belongs to BRS2-FM1-PM3 — SAMe Synthesis. Integrated cycle throughput belongs to BRS2-FM1-PM4 — Methionine Cycle Flux.
Homocysteine disposal through transsulfuration belongs to BRS2-FM2-PM5 — Transsulfuration Pathway. SAMe-dependent phospholipid methylation belongs to BRS2-FM3-PM7 — Phosphatidylcholine Formation. Later incorporation of DHA into neuronal membranes belongs to BRS1-FM3-PM7 — Neuronal Membrane DHA Incorporation.
B-vitamin effects on cognitive decline can depend on omega-3 status, but that interaction is a later, combined outcome, not a measurement of this reaction [Oulhaj et al. (2016) [4]].
(Integration within methylation-cycle efficiency)
Within BRS2(FM1) — Methylation Cycle Efficiency, this is the folate- and B12-dependent way to return homocysteine to methionine. The betaine route is parallel. SAMe formation uses the methionine product later. Folate supply explains where 5-methyltetrahydrofolate comes from. It does not, by itself, show that the wider set of methyl donors limits the tissue rate of this reaction.
4.1 Scientific Findings (3)
Summary
Human-pathway evidence establishes methionine synthase’s folate-substrate and methylcobalamin requirements and distinguishes them from upstream flavin-dependent enzymes. [9] In an adult observational study, riboflavin status modified the association between an MTHFR variant and circulating homocysteine. [10] Together, these findings clarify enzyme-specific dependence and a status–genotype interaction; the circulating marker does not directly measure tissue remethylation flux.
Methionine synthase transfers the methyl group of 5-methyltetrahydrofolate to homocysteine, producing methionine and tetrahydrofolate. Methylcobalamin carries that methyl group. Betaine remethylation, SAMe synthesis, transsulfuration and phospholipid methylation are different reactions.
What this means
This defines the reaction and its direct participants. It does not show that eating more folate or vitamin B12 speeds the reaction in human tissues, and it does not make riboflavin a cofactor of the synthase.
Evidence confidence: Not yet scored
Finding ID: PM1-F1
Finding Statement: Cobalamin-dependent methionine synthase transfers the methyl group of 5-methyltetrahydrofolate to homocysteine, producing methionine and tetrahydrofolate, and uses methylcobalamin as its cofactor. Betaine-dependent remethylation, methionine adenosyltransferase, transsulfuration and phosphatidylethanolamine methylation are separate reactions.
Synthesised Evidence Confidence: Not yet scored
Synthesis: A human-pathway review states the reaction directly: methionine synthase (MTR) converts homocysteine plus 5-methyltetrahydrofolate to methionine plus tetrahydrofolate and requires the methylated form of cobalamin. Methylenetetrahydrofolate reductase produces that folate substrate. Betaine-homocysteine methyltransferase is a separate, mainly liver and kidney route. Methionine adenosyltransferase then converts methionine to SAMe, and cystathionine beta-synthase starts transsulfuration. The review also traces dietary folate, including folic acid reduced by dihydrofolate reductase, into 5-methyltetrahydrofolate, and dietary cobalamin through absorption and intracellular processing onto the enzyme as methylcobalamin.
Synthesis Limitations: The primary source is a biochemical review, not a new human flux study. Reaction identity does not show that ordinary dietary intake controls tissue remethylation rate, and it does not assign clinical benefit. Phosphatidylethanolamine methylation is a later SAMe-consuming reaction, not part of this step.
Evidence Considered:
- Study
- Narrative review of cobalamin absorption, intracellular cofactor processing, folate-mediated one-carbon metabolism and methionine-cycle regulation.
- Population
- No new participants. The review synthesises human pathway biochemistry and inherited disorders of cobalamin and folate metabolism.
- Result
- Methionine synthase (MTR, EC 2.1.1.13) catalyses homocysteine plus 5-methyltetrahydrofolate to methionine plus tetrahydrofolate and requires methylcobalamin. Methylenetetrahydrofolate reductase produces 5-methyltetrahydrofolate. Betaine-homocysteine methyltransferase is an alternative remethylation enzyme, mainly in liver and kidney. Methionine adenosyltransferase converts methionine and ATP to SAMe. Cystathionine beta-synthase combines homocysteine with serine to start transsulfuration. Dietary folic acid is reduced to tetrahydrofolate by dihydrofolate reductase, and dietary cobalamin is processed to methylcobalamin on the synthase.
- Effect / Magnitude
- No new numeric effect size. The result is reaction identity and pathway separation.
- Evidence Summary
- Direct statement of the human methionine synthase reaction, its methylcobalamin cofactor, the folate route to its substrate, and the neighbouring reactions this PM does not include.
- Limitations
- A review does not measure tissue remethylation flux, ordinary-diet dose response, or a cognitive or attention outcome.
- Evidence Source
- Bounded external search
- Reference
- [9]
- Study
- Human reductase module crystallography and coenzyme-binding experiments.
- Population
- Recombinant human enzyme; no dietary participant cohort.
- Result
- Purified human methionine-synthase reductase contains both flavins and transfers reducing equivalents to methionine synthase.
- Effect / Magnitude
- No additional magnitude inferred.
- Evidence Summary
- Purified human methionine-synthase reductase contains both flavins and transfers reducing equivalents to methionine synthase.
- Limitations
- Foundational human-enzyme cofactor provenance supports capacity; it is not a measurement of dietary riboflavin-induced remethylation flux, brain methylation or benefit above adequacy. FMN is also required; FAD is the endpoint of the displayed activation chain, not its sole functional cofactor.
- Evidence Source
- Bounded external search
- Reference
- [12]
Connected / Supportive Evidence:
- Aragão et al. (2024) [2] — MechanisticWhy relevant: Riboflavin is often discussed beside folate-cycle enzymes, so this review was checked against the synthase reaction.Why excluded from the primary synthesis: Its abstract describes general riboflavin physiology. It does not state the methionine synthase reaction, methylcobalamin dependence, or separation from betaine remethylation.
Informs: Focus / Attention Stability; Cognitive Clarity
Riboflavin supplies the flavin cofactor of methylenetetrahydrofolate reductase, which makes 5-methyltetrahydrofolate, and of methionine synthase reductase, which repairs inactive cobalamin. Methionine synthase itself uses methylcobalamin.
What this means
Riboflavin can matter upstream of the substrate and in enzyme repair. It is not a cofactor bound at the methionine synthase catalytic site.
Evidence confidence: Not yet scored
Finding ID: PM1-F2
Finding Statement: Flavin adenine dinucleotide derived from riboflavin is a cofactor of methylenetetrahydrofolate reductase and of methionine synthase reductase, not of the methionine synthase catalytic site, which uses methylcobalamin.
Synthesised Evidence Confidence: Not yet scored
Synthesis: The human-pathway review assigns methylcobalamin, not a flavin, to methionine synthase, and places methylenetetrahydrofolate reductase upstream as the source of 5-methyltetrahydrofolate. An adult cross-sectional study states the same split: methylenetetrahydrofolate reductase uses FAD, methionine synthase reductase binds flavin mononucleotide and FAD, and methionine synthase uses methylcobalamin. In that study, riboflavin status modified the association of an MTHFR variant with blood homocysteine. That is a circulating-marker interaction at the upstream enzyme, not evidence that riboflavin occupies the synthase cofactor site.
Synthesis Limitations: The flavin assignment for the two neighbouring enzymes is stated in the study introduction from prior enzymology, and the new data are genotype associations with blood homocysteine. Neither source shows that dietary riboflavin changes tissue methionine-synthase flux.
Evidence Considered:
- Study
- Cross-sectional analysis of whether fasting plasma total homocysteine associations with MTHFR 677C>T, MTRR 66A>G and MTRR 524C>T depend on riboflavin status, measured by the erythrocyte glutathione reductase activation coefficient.
- Population
- 771 adults aged 18–75 years in Tarragona province, Spain, excluding B-vitamin users and pregnant or lactating women. Recruitment was in 1998–2002, before mandatory folic acid fortification of flour in that setting.
- Result
- The paper states that FAD is a cofactor of MTHFR, that MTRR binds flavin mononucleotide and FAD, and that methionine synthase uses methylcobalamin and is reactivated by MTRR. Among MTHFR 677T carriers with plasma folate below 14.7 nmol/L, blood homocysteine was 8.2% higher than in the 677CC genotype, and that difference was not seen when riboflavin status was optimal (interaction p = 0.048).
- Effect / Magnitude
- 8.2% higher blood homocysteine in the specified MTHFR contrast (p < 0.01), eliminated at optimal riboflavin status (interaction p = 0.048). No methionine-synthase activity or tissue-flux estimate is reported.
- Evidence Summary
- Separates the riboflavin-dependent enzymes (MTHFR and MTRR) from the methylcobalamin cofactor of methionine synthase, and shows a riboflavin-status interaction with an MTHFR variant on blood homocysteine.
- Limitations
- Observational genotype analysis. The endpoint is plasma homocysteine, not enzyme rate. Optimal riboflavin status did not identify riboflavin as a prosthetic group of methionine synthase.
- Evidence Source
- Bounded external search
- Reference
- [10]
Connected / Supportive Evidence:
- Froese et al. (2019) [9] — MechanisticWhy relevant: States that methionine synthase requires methylcobalamin and that methylenetetrahydrofolate reductase produces its folate substrate.Why excluded from the primary synthesis: It does not itself test riboflavin status or assign FAD to MTHFR or MTRR, so it is not the study that adjudicates the riboflavin split.
A small human tracer study measured increased whole-body remethylation and transmethylation after three weeks of folic acid; concentration changes did not establish those rates.
What this means
Pharmacological folic acid, not ordinary food folate, a deprivation trial or isolated tissue/whole-pool effect. Evidence access: Primary abstract.
Evidence confidence: Not yet scored
Finding ID: PM1-F6
Finding Statement: A small human tracer study measured increased whole-body remethylation and transmethylation after three weeks of folic acid; concentration changes did not establish those rates.
Synthesised Evidence Confidence: Not yet scored
Synthesis: A small human tracer study measured increased whole-body remethylation and transmethylation after three weeks of folic acid; concentration changes did not establish those rates.
Synthesis Limitations: Pharmacological folic acid, not ordinary food folate, a deprivation trial or isolated tissue/whole-pool effect. Evidence access: Primary abstract.
Evidence Considered:
- Study
- Three-week before/after folic acid with stable-isotope methionine kinetics
- Population
- 12 healthy subjects; 5 mg/day folic acid
- Result
- Whole-body remethylation increased 59% and transmethylation 20%; concentrations did not track kinetic changes.
- Effect / Magnitude
- No general dietary efficacy or tissue-uniform effect is inferred.
- Evidence Summary
- Whole-body remethylation increased 59% and transmethylation 20%; concentrations did not track kinetic changes.
- Limitations
- Pharmacological folic acid, not ordinary food folate, a deprivation trial or isolated tissue/whole-pool effect. Evidence access: Primary abstract.
- Evidence Source
- Bounded external search
- Reference
- [11]
5. BRS Pathways and Connections
5.1 BRS Pathways
BRS2-FM1-PM1 — Folate/B12-Dependent Homocysteine Remethylation ↓ BRS2-FM3-PM7 — Phosphatidylcholine Formation ↓ BRS1-FM3-PM7 — Neuronal Membrane DHA Incorporation
5.2 Cross-BRS Mechanism Relationships
Primary Mechanisms in other Biological Regulatory Systems that directly interact with, constrain or support this mechanism.
- BRS1-FM2-PM6 — Acetylcholine Synthesis Support — This reaction remethylates homocysteine with 5-methyltetrahydrofolate rather than betaine, so it is a parallel methyl route to the path that draws on choline. It supplies methionine, not the choline used for acetylcholine.
- BRS1-FM3-PM7 — Neuronal Membrane DHA Incorporation — Methionine from this reaction can later become SAMe and support phospholipid methylation. That is downstream use through other reactions, not a substrate step of methionine synthase.
5.3 Local BRS Mechanism Relationships
Related Primary Mechanisms within the same Biological Regulatory System that collectively support the integrated biological function.
- BRS2-FM1-PM2 — Betaine/BHMT Remethylation — Betaine-homocysteine methyltransferase also remethylates homocysteine, using betaine in liver and kidney and not 5-methyltetrahydrofolate or vitamin B12. Parallel route to the same methionine product.
- BRS2-FM1-PM3 — SAMe Synthesis — Methionine produced here is the amino-acid substrate for the later reaction that forms SAMe from methionine and ATP. Downstream use of the product, not part of methionine synthase.
- BRS2-FM1-PM4 — Methionine Cycle Flux — Cycle flux combines this remethylation step with SAMe use, homocysteine return and the parallel betaine route. Shared cycle context, not the synthase reaction itself.
7. Phenome Connections
These mappings are translational relationships, not single-mechanism outcome claims. Phenomes are emergent functional patterns supported by multiple interacting PMs across the BRAIN Framework.
Each Phenome relationship has two independent ratings. They are not combined or averaged.
Biology → Phenome Relationship Strength
How direct and important is this biological mechanism expected to be to the Phenome within the BRAIN model?
Evidence Confidence
How strongly does the adjudicated evidence support this particular biology → Phenome relationship?
- Biology → Phenome Relationship Strength: Low–Medium
- Evidence Confidence: Low–Medium
- Rationale: Children with ADHD have been reported to have lower folate and vitamin B12 than comparison groups, and one cohort of boys also had higher homocysteine Lukovac et al. (2024) [5]; Razavinia et al. (2024) [6]; Wang et al. (2019) [7]. Those are observational blood and diet differences. They do not show that methionine synthase activity is lower, and they do not show that folate or vitamin B12 supplementation improves attention. An MTHFR polymorphism meta-analysis concerns a folate-cycle enzyme upstream of this reaction, not methionine synthase flux Meng et al. (2022) [8].
Supporting evidence
Studies in children with ADHD report lower folate or vitamin B12, and sometimes higher homocysteine, than comparison groups. They do not measure methionine synthase activity or test whether changing it improves attention.
What this means
These associations are a ceiling on the attention relationship. They are not evidence that this reaction is impaired, and they are not a treatment result.
Evidence confidence: Not yet scored
Finding ID: PM1-F3
Finding Statement: Attached ADHD biomarker and MTHFR-genotype studies do not establish that folate- and B12-dependent methionine synthase activity modulates Focus / Attention Stability.
Synthesised Evidence Confidence: Not yet scored
Synthesis: A meta-analysis of observational studies found lower vitamin B9 and vitamin B12 in children with ADHD than in comparison children. A case-control study of boys found higher homocysteine and lower vitamin B12. A Taiwanese case-control study found lower serum folate and vitamin B12 together with a less favourable dietary pattern. A polymorphism meta-analysis linked an MTHFR variant to ADHD occurrence. None of these studies assayed methionine synthase, traced tissue remethylation, or tested folate or vitamin B12 as an attention treatment.
Synthesis Limitations: This is a bounded reading of the studies already attached to the attention relationship. It does not prove that no attention relationship exists. Heterogeneity is high in the vitamin meta-analysis, and the genotype paper concerns MTHFR, which is upstream of this reaction.
Evidence Considered:
- Study
- Systematic review and meta-analysis of case-control or cross-sectional studies of plasma vitamins B9 and B12 in children with ADHD, searched through June 2023.
- Population
- Six studies, 982 children aged about 6–12 years (204 girls and 744 boys; mean age 8.86 ± 2.03 years).
- Result
- Vitamin B9 differed between children with and without ADHD (standardised mean difference −0.80, 95% confidence interval −1.55 to −0.04). Vitamin B12 was lower in ADHD (standardised mean difference −0.29, 95% confidence interval −0.42 to −0.16). After sensitivity analysis the B12 difference remained (standardised mean difference −0.19, 95% confidence interval −0.34 to −0.04).
- Effect / Magnitude
- Vitamin B9 standardised mean difference −0.80 (−1.55 to −0.04). Vitamin B12 standardised mean difference −0.29 (−0.42 to −0.16), and −0.19 (−0.34 to −0.04) after sensitivity analysis. Heterogeneity for the B12 analysis was I² = 93% before that sensitivity analysis, then 21%.
- Evidence Summary
- Observational evidence of lower circulating folate and vitamin B12 in children with ADHD, without an enzyme or treatment measurement.
- Limitations
- Blood levels only, high heterogeneity before sensitivity analysis, no methionine-synthase assay and no supplementation outcome.
- Evidence Source
- Inherited repository evidence
- Reference
- [6]
- Study
- Cross-sectional serum comparison of homocysteine, vitamin B12, vitamin D, ferritin and iron, with behavioural and cognitive assessments.
- Population
- 133 boys aged 6.5–12.5 years, 67 with DSM-V ADHD and 66 age-matched boys without ADHD.
- Result
- Homocysteine was higher and vitamin B12 was lower in the ADHD group. Multiple logistic regression identified homocysteine as a potential prognostic indicator for ADHD.
- Effect / Magnitude
- The abstract reports statistically significant differences and does not give means, confidence intervals, or an enzyme-activity effect.
- Evidence Summary
- A single-sex paediatric case-control difference in two blood markers associated with one-carbon metabolism.
- Limitations
- Boys only, no folate measurement in the reported panel, no methionine-synthase assay, and no intervention. A prognostic association is not a causal test of this reaction.
- Evidence Source
- Inherited repository evidence
- Reference
- [5]
- Study
- Case-control study of food-frequency intake and fasting nutritional biochemistry, with a structural equation model linking diet, markers and ADHD.
- Population
- 216 children with ADHD and 216 age-, height- and sex-matched controls from 31 elementary schools in Taiwan.
- Result
- Compared with controls, children with ADHD had lower serum vitamin B12, folate, vitamin B6, ferritin and monounsaturated fatty acids, and higher saturated fatty acids, n-6/n-3 ratio and inorganic phosphorus. They reported more nutrient-poor, high-sugar and high-fat foods and less vegetable, fruit and protein-rich food. The model treated poor nutritional biochemistry as a link between unhealthy diet and ADHD.
- Effect / Magnitude
- The abstract reports significant group differences and does not give mean differences for folate or vitamin B12, or any synthase-flux estimate.
- Evidence Summary
- Human observational evidence that diet pattern and several blood nutrients, including folate and vitamin B12, differ by ADHD status.
- Limitations
- Cross-sectional path analysis cannot show that methionine synthase activity changed, or that correcting folate or vitamin B12 improves attention. Several non-B-vitamin markers differed as well.
- Evidence Source
- Inherited repository evidence
- Reference
- [7]
- Study
- Random-effects meta-analysis of case-control studies of MTHFR 677C>T and 1298A>C in ADHD, bipolar disorder and schizophrenia.
- Population
- Five ADHD studies (434 cases and 670 controls), plus separate bipolar and schizophrenia study sets. Cases and controls were defined by the included psychiatric studies, not by a shared remethylation assay.
- Result
- MTHFR 677C>T was associated with bipolar disorder and schizophrenia. MTHFR 1298A>C was related to ADHD and bipolar disorder. Sensitivity analyses were described as stable. No methionine-synthase genotype or enzyme activity was analysed.
- Effect / Magnitude
- Associations were summarised as odds ratios. The abstract does not give the ADHD odds ratio, and it reports no remethylation-flux effect.
- Evidence Summary
- Genetic association of an upstream folate-cycle enzyme variant with ADHD occurrence, not a test of methionine synthase capacity.
- Limitations
- MTHFR is upstream of 5-methyltetrahydrofolate supply. Genotype association does not establish enzyme flux, dietary response, or an attention benefit from folate or vitamin B12.
- Evidence Source
- Inherited repository evidence
- Reference
- [8]
Informs: Focus / Attention Stability
- Biology → Phenome Relationship Strength: Low–Medium
- Evidence Confidence: Low
- Rationale: Folic acid, with or without vitamin B12, lowers blood homocysteine Collaboration (1998) [1]. In older adults with mild cognitive impairment, B-vitamin treatment was associated with slower cognitive decline only when omega-3 status was higher Oulhaj et al. (2016) [4]. Blood homocysteine and that combined B-vitamin interaction do not measure methionine synthase flux, and they do not establish that this reaction itself changes cognitive clarity.
Supporting evidence
In older adults with mild cognitive impairment, B vitamins were associated with slower cognitive decline only when omega-3 status was higher. That interaction does not measure methionine synthase flux.
What this means
A conditional cognitive signal in mild cognitive impairment is not evidence that this reaction modulates cognitive clarity, and it is not an attention-treatment result.
Evidence confidence: Not yet scored
Finding ID: PM1-F4
Finding Statement: B-vitamin effects on cognitive decline in mild cognitive impairment, including an interaction with omega-3 status, do not measure methionine synthase flux or establish that this reaction modulates Cognitive Clarity.
Synthesised Evidence Confidence: Not yet scored
Synthesis: Re-analysis of a two-year trial in mild cognitive impairment found better cognitive and clinical scores with B vitamins as baseline omega-3 status rose, and no B-vitamin effect on cognitive decline when omega-3 status was low. The intervention combined folic acid, vitamin B6 and vitamin B12. Blood homocysteine lowering by folic acid and vitamin B12 is a separate circulating-marker result. Neither dataset isolates methionine synthase activity from other B-vitamin actions or from omega-3-dependent membrane biology.
Synthesis Limitations: One re-analysis in adults aged 70 years and older with mild cognitive impairment, using a three-vitamin intervention. It does not test children, attention outcomes, or tissue remethylation rate. The omega-3 interaction places part of the signal outside this reaction.
Evidence Considered:
- Study
- Re-analysis of the VITACOG randomised trial testing whether baseline plasma omega-3 status interacted with B-vitamin treatment on cognitive and clinical scores.
- Population
- 266 participants with mild cognitive impairment, aged 70 years or older, randomised to folic acid plus vitamins B6 and B12, or placebo, for 2 years.
- Result
- Final verbal delayed recall, global cognition and clinical dementia rating improved in the B-vitamin group as baseline omega-3 concentration increased, with little relation to omega-3 status in the placebo group. Among participants with good omega-3 status, 33% on B vitamins had a global clinical dementia rating above 0, compared with 59% on placebo. Docosahexaenoic acid, more than eicosapentaenoic acid, carried the interaction. When omega-3 status was low, B vitamins had no effect on cognitive decline.
- Effect / Magnitude
- 33% versus 59% with global clinical dementia rating above 0 in the good omega-3 stratum. No methionine-synthase activity or tissue-flux estimate is reported.
- Evidence Summary
- Human outcome evidence that a combined B-vitamin intervention interacts with omega-3 status on cognitive decline in mild cognitive impairment.
- Limitations
- Not a test of methionine synthase alone. Vitamin B6, which acts in transsulfuration rather than this reaction, was part of the intervention. The result is conditional on omega-3 status and does not establish a general cognitive-clarity benefit.
- Evidence Source
- Inherited repository evidence
- Reference
- [4]
Connected / Supportive Evidence:
- Collaboration (1998) [1] — Human MechanisticWhy relevant: Shows that folic acid and vitamin B12 lower blood homocysteine, the marker often used to interpret B-vitamin cognitive trials.Why excluded from the primary synthesis: The meta-analysis measured blood homocysteine, not cognitive clarity and not tissue methionine-synthase flux. That marker limit is assessed in PM1-IC1.
Informs: Cognitive Clarity
8. References
- [1] Collaboration (1998) — Lowering Blood Homocysteine with Folic Acid Based Supplements
- [2] Aragão et al. (2024) — Unveiling Its Timeless Significance in Human Physiology and Health
- [3] Tao Huang et al. (2015) — A Randomized Controlled Trial
- [4] Oulhaj et al. (2016) — Omega-3 Fatty Acid Status Enhances the Prevention of Cognitive Decline by B
- [5] Lukovac et al. (2024) — Serum Biomarker Analysis in Pediatric ADHD
- [6] Razavinia et al. (2024) — Vitamins B ₉ and B ₁₂ in Children with Attention Deficit Hyperactivity
- [7] Wang et al. (2019) — Path Analysis for a Case-Control Study
- [8] Meng et al. (2022) — A Meta-analysis
- [9] Froese et al. (2019) — Vitamin B12, Folate and Methionine Remethylation
- [10] García-Minguillán et al. (2014) — Riboflavin Status, MTHFR, MTRR and Homocysteine
- [11] Stam et al. (2005) — Folic Acid and Whole-Body Methyl Flux
- [12] Wolthers et al. (2007) — Mechanism of coenzyme binding to human methionine synthase reductase
Foods supply the named dietary input. They are not shown as containing the downstream metabolite. Conversion evidence does not establish a new downstream PM admission, effective dose or equivalent food intervention.
Vitamin B2 → Riboflavin kinase (RFK) phosphorylates riboflavin to FMN using ATP. → Flavin mononucleotide (FMN)
BRS2-FM1-PM1: Recycle homocysteine to methionine through folate and B12 so methyl-donor supply and homocysteine control stay supported.
Existing admission: Type A / derived; versioned-assessment. Production context for an already admitted substrate; no new metabolite-to-PM relationship is admitted.
Foundational human-enzyme cofactor provenance supports capacity; it is not a measurement of dietary riboflavin-induced remethylation flux, brain methylation or benefit above adequacy. FMN is also required; FAD is the endpoint of the displayed activation chain, not its sole functional cofactor.
- Almonds — supplies Vitamin B2; verified; form not known. Nuts, almonds
Composition provenance
USDA SR Legacy April 2018
- Beef — supplies Vitamin B2; verified; raw. Beef, ground, 85% lean meat / 15% fat, raw (Includes foods for USDA's Food Distribution Program)
Composition provenance
USDA SR Legacy April 2018
- Broccoli — supplies Vitamin B2; verified; raw. Broccoli, raw
Composition provenance
USDA SR Legacy April 2018
- Kale — supplies Vitamin B2; verified; raw. Kale, raw
Composition provenance
USDA SR Legacy April 2018
- Milk — supplies Vitamin B2; verified; form not known. Milk, whole, 3.25% milkfat, with added vitamin D
Composition provenance
USDA SR Legacy April 2018
- Nori — supplies Vitamin B2; verified; dried. Purple laver (Porphyra spp.), dried, toasted
Composition provenance
MEXT Standard Tables of Food Composition in Japan (2023 supplement), food 09004
- Nutritional Yeast — supplies Vitamin B2; verified; dried. Marigold Engevita Nutritional Yeast Flakes with B12, dried inactive Saccharomyces cerevisiae
Composition provenance
Marigold Health Foods label
- Quinoa — supplies Vitamin B2; verified; uncooked. Quinoa, uncooked
Composition provenance
USDA SR Legacy April 2018
- Salmon Roe — supplies Vitamin B2; verified; form not known. Chum salmon (Oncorhynchus keta), salted roe (ikura)
Composition provenance
MEXT Standard Tables of Food Composition in Japan (2023 supplement), food 10140
- Spinach — supplies Vitamin B2; verified; raw. Spinach, raw
Composition provenance
USDA SR Legacy April 2018
Enzyme identity does not quantify tissue cofactor supply or flux after a meal.
Dependencies: Functional RFK; ATP and divalent metal availability
Vitamin B2 → Riboflavin kinase (RFK) phosphorylates riboflavin to FMN using ATP. → FLAD1 FAD synthase adenylates FMN with ATP to form FAD. → Flavin adenine dinucleotide (FAD)
BRS2-FM1-PM1: Recycle homocysteine to methionine through folate and B12 so methyl-donor supply and homocysteine control stay supported.
Existing admission: Type A / derived; versioned-assessment. The complete derived relationship is admitted for this PM.
Foundational human-enzyme cofactor provenance supports capacity; it is not a measurement of dietary riboflavin-induced remethylation flux, brain methylation or benefit above adequacy. FMN is also required; FAD is the endpoint of the displayed activation chain, not its sole functional cofactor.
- Almonds — supplies Vitamin B2; verified; form not known. Nuts, almonds
Composition provenance
USDA SR Legacy April 2018
- Beef — supplies Vitamin B2; verified; raw. Beef, ground, 85% lean meat / 15% fat, raw (Includes foods for USDA's Food Distribution Program)
Composition provenance
USDA SR Legacy April 2018
- Broccoli — supplies Vitamin B2; verified; raw. Broccoli, raw
Composition provenance
USDA SR Legacy April 2018
- Kale — supplies Vitamin B2; verified; raw. Kale, raw
Composition provenance
USDA SR Legacy April 2018
- Milk — supplies Vitamin B2; verified; form not known. Milk, whole, 3.25% milkfat, with added vitamin D
Composition provenance
USDA SR Legacy April 2018
- Nori — supplies Vitamin B2; verified; dried. Purple laver (Porphyra spp.), dried, toasted
Composition provenance
MEXT Standard Tables of Food Composition in Japan (2023 supplement), food 09004
- Nutritional Yeast — supplies Vitamin B2; verified; dried. Marigold Engevita Nutritional Yeast Flakes with B12, dried inactive Saccharomyces cerevisiae
Composition provenance
Marigold Health Foods label
- Quinoa — supplies Vitamin B2; verified; uncooked. Quinoa, uncooked
Composition provenance
USDA SR Legacy April 2018
- Salmon Roe — supplies Vitamin B2; verified; form not known. Chum salmon (Oncorhynchus keta), salted roe (ikura)
Composition provenance
MEXT Standard Tables of Food Composition in Japan (2023 supplement), food 10140
- Spinach — supplies Vitamin B2; verified; raw. Spinach, raw
Composition provenance
USDA SR Legacy April 2018
Enzyme identity does not quantify tissue cofactor supply or flux after a meal.
Dependencies: Functional RFK; ATP and divalent metal availability
FAD production and enzyme loading depend on cellular context; no fixed food-to-FAD yield is inferred.
Dependencies: Functional FLAD1 FAD synthase; ATP and divalent metal availability