What happens when you take vitamin b12 with folate?
Vitamin B12 and folate (vitamin B9) are the two most tightly coupled vitamins in human biochemistry. They share a single critical reaction, and each one depends on the other to do its job.
- They meet at one enzyme. The enzyme methionine synthase converts homocysteine back into methionine. Folate, in its active 5-methyltetrahydrofolate form, supplies the methyl group, and vitamin B12, in its methylcobalamin form, is the cofactor that hands that methyl group off.
- A shortfall of either one stalls the same pathway. Without enough folate, the methyl group is unavailable. Without enough B12, the enzyme cannot transfer it. Both shortfalls push homocysteine up and slow DNA synthesis.
- Red blood cells suffer either way. When DNA synthesis slows, developing red blood cells become abnormally large (the megaloblastic anemia seen in both folate and B12 deficiency), so the blood picture can look the same regardless of which vitamin is missing.
- But folate cannot fully cover for B12. High folate intake can keep the blood symptoms at bay by pushing DNA synthesis along a folate-only side route, yet the nervous system still depends on B12 in ways folate cannot replace. That asymmetry is the heart of why the pair matters clinically.
Why is this important?
The main reason to keep B12 and folate together is the folate-masking problem. High-dose folic acid can correct the anemia of B12 deficiency, so blood counts and energy normalize, while the underlying B12 deficiency keeps quietly damaging the spinal cord and peripheral nerves. By the time symptoms appear, some of that nerve injury can be permanent (a condition called subacute combined degeneration).
This is why over-the-counter folic acid is kept to modest amounts and why clinicians check B12 status before treating with folate. It is also why prenatal vitamins and B-complex products almost always include B12 alongside folate.
Beyond safety, the pair works together to support homocysteine balance. In a large meta-analysis of randomised trials, folic acid did most of the work in lowering blood homocysteine, with B12 adding a further, smaller reduction on top — more than folate alone. That combined effect is the rationale for using B-vitamin combinations in pregnancy, in older adults, and in people with cardiovascular risk factors.
What should you do?
Before any change: if you are considering high-dose folate, or you fall into a higher-risk group, have your B12 status checked first and review the plan with your doctor or pharmacist. This is the single most important step, because it prevents folate from masking a B12 problem.
Every day: take folate and B12 together. A standard B-complex, prenatal vitamin, or daily multivitamin pairs them automatically at sensible ratios, so no separate timing or dosing is needed.
After a change: if you start metformin or a proton pump inhibitor, become vegan or vegetarian, or simply get older, ask your clinician to check your B12 level periodically, since absorption can decline. If you have B12-related neurologic symptoms, methylcobalamin is the form some clinicians prefer, but both methylcobalamin and cyanocobalamin are effective.
For people with MTHFR gene variants, the methylated form of folate (5-MTHF or L-methylfolate) can be helpful, but plain folic acid works well for the general population. Whatever the form, avoid high-dose folate on its own for extended periods without medical supervision.
Which specific products are affected?
Virtually every B-complex, multivitamin, and prenatal vitamin already combines B12 and folate at sensible ratios, so the pairing is the industry default. Common examples include Centrum, One A Day, Theragran, B-50 and B-100 complexes, Thorne Basic B Complex, and Pure Encapsulations B-Complex Plus. Prenatal vitamins routinely contain both vitamins together.
The products to be more careful with are the standalone ones: high-dose prescription folic acid tablets, and standalone B12 injections or lozenges. These are worth reviewing with a clinician, especially in older adults. Methylated combination products such as Thorne Methyl-Guard and Designs for Health Homocysteine Supreme pair methylfolate with methylcobalamin specifically for homocysteine support.
The science behind it
The interdependence of B12 and folate at methionine synthase, and folate's ability to mask B12-deficiency anemia while nerve damage progresses, are well established in the literature.
- Homocysteine Lowering Trialists' Collaboration, BMJ 1998 — a meta-analysis of randomised trials found that folic acid produced the largest reduction in blood homocysteine, with vitamin B12 adding a further reduction on top, confirming the additive benefit of the pair. (https://pmc.ncbi.nlm.nih.gov/articles/PMC28491/)
- Selhub J, et al. Am J Clin Nutr 2009 (PMC2647758) — a population study examining the folate-vitamin B12 interaction in relation to cognitive impairment, anemia, and biochemical markers of B12 deficiency, supporting the clinical relevance of keeping the two in balance. (https://pmc.ncbi.nlm.nih.gov/articles/PMC2647758/)
- NIH Office of Dietary Supplements, Vitamin B12 Fact Sheet for Health Professionals — describes methionine synthase and homocysteine remethylation, and notes that B12-related neurologic damage can occur even without anemia. (https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/)
Frequently Asked Questions
Can I take vitamin B12 and folate at the same time?
Yes. They are designed to work together, and most B-complex, multivitamin, and prenatal products combine them in one dose. There is no need to space them apart.
Why is taking folate alone a concern?
High-dose folate can correct the anemia caused by B12 deficiency, making blood counts and energy look normal, while the underlying B12 deficiency continues to damage nerves. Pairing folate with B12, and checking B12 status before high-dose folate, prevents this.
Do I need the methylated forms (5-MTHF and methylcobalamin)?
For people with MTHFR gene variants or B12-related neurologic symptoms, the methylated forms can be preferred. For the general population, plain folic acid and cyanocobalamin are also effective.
Who is most at risk of low B12?
Adults over 50, vegans and vegetarians, and people taking metformin or proton pump inhibitors long-term tend to absorb less B12 and may need their levels checked periodically.
Is this combination safe during pregnancy?
Folate and B12 together are routine in prenatal care, since folate supports healthy neural tube development. Use a prenatal vitamin as directed by your clinician rather than improvising high doses.
Do I need to check my levels before supplementing?
For ordinary multivitamin or B-complex amounts, routine testing usually is not required. Before using high-dose folate on its own, confirm your B12 status with your doctor or pharmacist.
Key takeaways
- Vitamin B12 and folate share one enzyme (methionine synthase) and depend on each other to support DNA synthesis, red blood cells, and homocysteine balance.
- The real risk is taking high-dose folate alone, which can mask B12 deficiency while nerve damage progresses unnoticed.
- A standard B-complex, multivitamin, or prenatal pairs them safely and automatically.
- Confirm your B12 status before high-dose folate, and review the plan with your doctor or pharmacist.
- Adults over 50, vegans and vegetarians, and people on metformin or PPIs should have B12 checked periodically.