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Supplement × Supplement·Evidence index

Vitamin B12 and Vitamin B9: what the research found

PubMed indexes 8 records that name Vitamin B12 and Vitamin B9 together, either in the title or in an interaction, co-administration, or pharmacokinetic context. The key findings come first, in the authors’ own words, followed by every study with its design and PubMed link.

A summary of published research, not medical advice. A pharmacist can check any combination against your full list of medicines and supplements.

Key findings

What the studies concluded.

Reviews and human studies first. Each quote is the authors’ own conclusion about their study, not a NutriStack assessment, and a single study is not a consensus.

“MS patients tend to have elevated Hcy blood levels compared to healthy controls. Hcy may contribute to the pathogenesis of the disease.”

Dardiotis et al. · 2017 · Review or meta-analysis · details

“The evidence for excess folic acid exacerbating B12 deficiency is primarily correlative or from uncontrolled clinical observations, and the hypothesis to explain the phenomenon has not yet been tested. Nonetheless, the evidence is sufficiently compelling to warrant increased vigilance for identifying B12 deficiency in at risk individuals, including older adults and others with low B12 intake or conditions that…”

Miller et al. · 2024 · Human study · details

“Exceptions are Imerslund-Gräsbeck syndrome and hereditary folate malabsorption (affecting intestinal absorption of cobalamin and folate, respectively), transcobalamin deficiency (affecting transport of cobalamin in blood and cellular cobalamin uptake), and methylenetetrahydrofolate dehydrogenase 1 deficiency (catalyzing cytoplasmic interconversion of reduced folate coenzyme derivatives).”

The research

8 studies naming Vitamin B12 and Vitamin B9.

Strongest relevance first: papers naming both substances in the title, then human trials and systematic reviews.

High-Folate-Low-Vitamin B12 Interaction Syndrome.

European journal of case reports in internal medicine · 2025 · PMID 40502959

“All the patients with neurological signs and symptoms should be tested for possible vitamin B12 deficiency: early diagnosis and treatment could stop the progression of the disease and allow the regression of the neurological deficit. It is important not to rely on blood count values to diagnose a vitamin B12 deficiency as the neurological and haematological outlook may be inversely proportional.”

Cicchini et al. · Authors' conclusion

Names both Vitamin B12 and Vitamin B9 in its title.

Excess Folic Acid and Vitamin B12 Deficiency: Clinical Implications?

Food and nutrition bulletin · 2024 · PMID 38987872

ReviewResearch Support, N.I.H., ExtramuralResearch Support, U.S. Gov't, Non-P.H.S.Human subjects

“The evidence for excess folic acid exacerbating B12 deficiency is primarily correlative or from uncontrolled clinical observations, and the hypothesis to explain the phenomenon has not yet been tested. Nonetheless, the evidence is sufficiently compelling to warrant increased vigilance for identifying B12 deficiency in at risk individuals, including older adults and others with low B12 intake or conditions that are associated with B12 malabsorption, who also ingest excessive…”

Miller et al. · Authors' conclusion

Names both Vitamin B12 and Vitamin B9 in its title.

Role of Vitamin B12 and Folate in Metabolic Syndrome.

Cureus · 2021 · PMID 34754676

Review

“According to the literature, vitamin B12 and folate supplementation, along with a host of novel therapies, has a considerable positive impact on MS. These findings must be kept in mind while designing newer treatment protocols in the future.”

Ashok et al. · From the abstract

Names both Vitamin B12 and Vitamin B9 in its title.

Immunodeficiency and inborn disorders of vitamin B12 and folate metabolism.

Current opinion in clinical nutrition and metabolic care · 2020 · PMID 32412981

ReviewHuman subjects

“Exceptions are Imerslund-Gräsbeck syndrome and hereditary folate malabsorption (affecting intestinal absorption of cobalamin and folate, respectively), transcobalamin deficiency (affecting transport of cobalamin in blood and cellular cobalamin uptake), and methylenetetrahydrofolate dehydrogenase 1 deficiency (catalyzing cytoplasmic interconversion of reduced folate coenzyme derivatives).”

Watkins et al. · From the abstract

Names both Vitamin B12 and Vitamin B9 in its title.

Folic Acid and Vitamin B12 Administration in CKD, Why Not?

Nutrients · 2019 · PMID 30781775

ReviewHuman subjects

“In addition, folic acid and vitamin B12 could not only be mere cofactors in the homocysteine metabolism; they may have a direct action in determining tissue damage and cardiovascular risk. The purpose of this review was to highlight homocysteine, folic acid and vitamin B12 metabolism impairment in CKD and ESRD and to summarize available evidences on hyperhomocysteinemia, folic acid and vitamin B12 as cardiovascular risk markers, therapeutic target and risk factors for CKD…”

Capelli et al. · From the abstract

Names both Vitamin B12 and Vitamin B9 in its title.

Interaction between excess folate and low vitamin B12 status.

Molecular aspects of medicine · 2017 · PMID 27876554

ReviewResearch Support, U.S. Gov't, Non-P.H.S.Human subjects

“Pregnant women are exposed to folic acid at varying doses depending on the prenatal care prescribed in different countries. This review summarizes the current knowledge on the interaction between folate and vitamin B12 and the associated health outcomes.”

Paul et al. · From the abstract

Names both Vitamin B12 and Vitamin B9 in its title.

Vitamin B12, folic acid, and bone.

Current osteoporosis reports · 2013 · PMID 23873438

ReviewHuman subjects

“It is uncertain whether supplementation with vitamin B12 and folate can decrease fracture incidence. One double blind clinical trial in post-stroke patients showed that these B vitamins could decrease hip fracture incidence, but the results of further clinical trials should be awaited before a definite conclusion can be drawn.”

Swart et al. · From the abstract

Names both Vitamin B12 and Vitamin B9 in its title.

Limitations

What this evidence cannot tell you.

Search-based evidence indexes have real limits, and it is worth being explicit about them:

How to read this page

A literature summary, not guidance.

NutriStack

Track what you actually take.

NutriStack is a free iPhone app for organising a supplement routine: what you take, when, and what the published record says about it. Its exploratory interaction checker covers Vitamin B12, Vitamin B9, and several hundred other substances.

Log your routine, get reminders at the times you choose, and scan a label to add a product. The checker is a research and organisation tool, not a clinical decision aid.

NutriStack is an informational and organizational tool, not a medical service, and not a substitute for professional advice. Always consult a qualified healthcare professional before starting, stopping, or changing any supplement or medication.