Vitamin B12 is essential for healthy nerves: the body needs it to build myelin, the protective sheath around nerve fibers, and for the normal development and function of the brain and spinal cord. When B12 runs low, nerve-related signs such as numbness, tingling or balance problems can appear, sometimes before any change in the blood count. Those signs are a reason to get tested, because B12 helps nerves when a shortfall is part of the picture, and many other things can cause the same symptoms.
Key Takeaways
- B12 is required for myelination and function of the central nervous system, healthy red blood cells and DNA synthesis.
- Numbness or tingling in the hands and feet, balance problems, confusion and memory changes can be signs of low B12, and they can occur without anemia. A blood test is the only way to know.
- Adults need 2.4 mcg a day (2.6 mcg in pregnancy, 2.8 mcg while breastfeeding). B12 comes naturally only from animal foods, so vegans rely on fortified foods or supplements.
- No supplement form of B12 has been shown to be better absorbed than another; cyanocobalamin and methylcobalamin are both common.
- Long-term use of metformin or acid-reducing medicines is linked to lower B12 levels. Ask your doctor about testing if you take them.
- Nerve changes from long-lasting low B12 may not fully reverse if it goes untreated, so early testing matters.
Evidence grade: Strong. B12's role in myelin and nerve function, its NIH recommended intakes and the neurological effects of deficiency are well established in NIH fact sheets and clinical reviews; supplements are studied mainly for raising low B12 levels.
What Vitamin B12 Does for Your Nerves
Vitamin B12, also called cobalamin, is a water-soluble vitamin. According to the NIH Office of Dietary Supplements (ODS), it is required for the development, myelination and function of the central nervous system, for healthy red blood cell formation and for making DNA.
Myelin and nerve signaling
Myelin is the fatty insulation that wraps many nerve fibers and helps signals travel quickly and cleanly. B12 is needed to form and maintain it. When B12 is low for a long time, nerves can be affected, and numbness and tingling in the hands and feet are among the classic signs.
The two jobs B12 does inside cells
B12 works as a helper for two enzymes. The first, methionine synthase, turns homocysteine into the amino acid methionine. Methionine is used to make S-adenosylmethionine, a "methyl donor" the body uses to modify DNA, RNA, proteins and fats. The second enzyme converts methylmalonyl-CoA into succinyl-CoA as part of energy metabolism. When B12 is short, homocysteine and methylmalonic acid (MMA) build up, and doctors can measure both in the blood. A 2017 expert review describes B12's central roles in DNA synthesis, methylation and mitochondrial metabolism.
For the full nutrient profile, including foods and absorption, see our vitamin B12 guide. To see how B12 works with the rest of its family, read how B vitamins affect the nervous system.
Signs of Low B12 That Are Worth a Blood Test
The body stores a lot of B12, about 1 to 5 mg, so a shortfall can take years to show. ODS and MedlinePlus list these signs:
- Nerve-related: numbness or tingling in the hands and feet, loss of balance, confusion, poor memory and low mood.
- Blood-related: tiredness, weakness, pale skin and heart palpitations, which come from a type of anemia with large red blood cells.
- Other: a sore mouth or tongue, loss of appetite and weight loss.
Two points matter most. First, ODS notes that nerve symptoms can appear without anemia, so a normal blood count does not rule out low B12. Second, MedlinePlus explains that long-term deficiency can cause nerve damage that may be permanent if treatment does not start promptly after symptoms begin. These symptoms also overlap with many other conditions, so the right step is a conversation with your doctor and a blood test, not guessing.
How B12 is tested
The usual first test is a serum or plasma B12 level. Labs set their own cut-offs; ODS notes most consider values below 200 or 250 pg/mL low, while MedlinePlus lists a normal range of about 299 to 1,054 pg/mL. When results are borderline, doctors may check methylmalonic acid, the most sensitive marker of B12 status.
Who Is More Likely to Run Low
- Older adults. Many have less stomach acid, which is needed to release B12 from food. ODS advises people over 50 to get most of their B12 from fortified foods or supplements, which are easier to absorb.
- Vegans and vegetarians. Plant foods do not naturally contain B12. Fortified cereals, fortified nutritional yeast and supplements fill the gap.
- People with absorption problems. This includes people who lack intrinsic factor, a stomach protein needed to absorb B12, people with certain digestive conditions and people who have had stomach or intestinal surgery, including weight-loss surgery.
- People taking certain medicines long term, such as metformin or acid reducers (see Safety and Interactions below).
Absorption is a big part of the story. Our article on how to improve B12 absorption covers it in more detail.
How Much Vitamin B12 You Need
The Recommended Dietary Allowance (RDA) for adults is set to keep blood counts and B12 levels healthy. Food comes first, and a few servings of animal foods or fortified foods easily cover it.
| Group | RDA per day | Food source (per serving) | B12 |
|---|---|---|---|
| Adults and teens 14+ | 2.4 mcg | Clams, cooked, 3 oz | 17 mcg |
| Pregnancy | 2.6 mcg | Fortified nutritional yeast, about 1/4 cup | 8.3 to 24 mcg |
| Breastfeeding | 2.8 mcg | Salmon, Atlantic, cooked, 3 oz | 2.6 mcg |
| Children 9 to 13 | 1.8 mcg | Ground beef, 85% lean, 3 oz | 2.4 mcg |
| Children 4 to 8 | 1.2 mcg | Milk, 2%, 1 cup | 1.3 mcg |
| Children 1 to 3 | 0.9 mcg | Egg, 1 large | 0.5 mcg |
ODS notes that B12 from dairy appears to be absorbed about three times better than B12 from meat, fish and poultry, and B12 from supplements about 50% better than from food.
Forms of Vitamin B12 in Supplements
Supplements use four main forms: cyanocobalamin (the most common), methylcobalamin, adenosylcobalamin and hydroxocobalamin. Methylcobalamin and adenosylcobalamin are the forms the body uses directly; the others are converted into them. ODS states that no evidence shows absorption differs by form, and that research has not shown any form to be better than the others. Sublingual (under-the-tongue) B12 is also sold.
Dose matters more than form. The body absorbs about half of a small dose of 1 to 2 mcg, but only about 2% of a 500 mcg dose and 1.3% of a 1,000 mcg dose, because the intrinsic-factor system that absorbs B12 fills up quickly.
| Product type | Typical B12 amount | Notes |
|---|---|---|
| Multivitamin/mineral | 5 to 25 mcg | Above the RDA for most adults |
| B-complex | 50 to 500 mcg | Combined with other B vitamins |
| B12-only supplement | 500 to 1,000 mcg | Only a small percentage is absorbed at these doses |
| Injection (prescription) | Set by a clinician | Bypasses absorption problems |
Dosing: Everyday Intake Versus Correcting Low Levels
For people with normal B12 levels, meeting the RDA through food, fortified foods or a multivitamin is the goal. Correcting a diagnosed deficiency is different and should be guided by your clinician.
Injections have long been the usual approach because they bypass absorption barriers. A 2018 Cochrane review of three randomized trials with 153 participants found that high oral doses of 1,000 to 2,000 mcg a day raised blood B12 levels about as well as injections over three to four months. The evidence was rated low quality, and the right route depends on why B12 is low. People who lack intrinsic factor, for example, are usually treated with injections, although very high oral doses may also work.
If you are comparing B vitamins for nerve support more broadly, our guide to B-complex dosage covers B12 alongside the other B vitamins.
Getting B12 from a daily multivitamin
If your aim is simply to cover the RDA, a multivitamin is one convenient route. OPA Women's Daily Multivitamin lists vitamin B12 in its B-vitamin complex, alongside thiamine, riboflavin, niacin, vitamin B6, folate, biotin and pantothenic acid, to support energy metabolism. Check the Supplement Facts panel for the exact B12 amount. For comparison, ODS reports that multivitamins typically contain 5 to 25 mcg, which covers the 2.4 mcg RDA but is far below the 1,000 to 2,000 mcg doses used to correct a diagnosed deficiency. A multivitamin is not a substitute for testing if you have nerve-related symptoms.
Safety and Interactions
- Upper limit: no Tolerable Upper Intake Level has been set for B12 because of its low potential for toxicity.
- Metformin: metformin may reduce B12 absorption. In the long-running Diabetes Prevention Program Outcomes Study, borderline-low B12 was about twice as common in the metformin group as in the placebo group after 5 years (19.1% vs 9.5%), and risk rose with each year of use. If you take metformin, talk to your doctor about checking your B12.
- Acid-reducing medicines: proton pump inhibitors (such as omeprazole or lansoprazole) and H2 blockers (such as cimetidine) can reduce B12 absorption from food. In a study of more than 25,000 people with low B12, a 2-year or longer supply of a proton pump inhibitor was linked to 65% higher odds of deficiency, and of an H2 blocker to 25% higher odds. Talk to your doctor or pharmacist if you use these long term.
- Do not self-manage nerve symptoms: numbness, tingling, weakness or balance problems need a medical evaluation, whatever the cause.
- Multivitamins with botanicals: some multivitamins contain herbal blends. If you take prescription medicines, ask your pharmacist to review the full ingredient list.
- Pregnancy and breastfeeding: needs are higher (2.6 and 2.8 mcg). Infants breastfed by mothers on vegan diets can develop low B12, so talk to your healthcare provider about B12 if you follow a vegan diet while pregnant or breastfeeding.
Frequently Asked Questions
How does vitamin B12 help the nervous system?
B12 is required to form and maintain myelin, the protective coating around nerve fibers, and for the normal development and function of the brain and spinal cord. It also helps recycle homocysteine and supports DNA synthesis and energy metabolism inside cells.
What are the most common nerve-related signs of low B12?
Numbness or tingling in the hands and feet and problems with balance are the classic signs. Confusion, memory problems and low mood can also occur. These signs can appear without anemia, so see your doctor and ask about a B12 test.
Can nerve symptoms from low B12 get better?
It depends on how long the deficiency lasted and how quickly it is treated. MedlinePlus notes that nerve damage from long-term low B12 may be permanent if treatment does not start promptly after symptoms begin, which is why early testing matters.
How much B12 should I take for nerve health?
If your levels are normal, the goal is the RDA of 2.4 mcg a day for adults, which food, fortified foods or a multivitamin can cover. If a test shows low B12, your clinician will choose the dose and route; trials of oral treatment used 1,000 to 2,000 mcg a day.
Is methylcobalamin better than cyanocobalamin?
ODS says research has not shown that any form of supplemental B12 is better than the others, and no evidence shows absorption differs by form. Cyanocobalamin is the most common and is converted by the body into the active forms.
Is a B-complex helpful for nerve health?
A B-complex supplies B12 together with other B vitamins, usually with 50 to 500 mcg of B12 according to ODS. Whether you need one depends on your diet, your test results and any medicines you take, so ask your healthcare provider which option and amount suit you.
Sources
- NIH Office of Dietary Supplements. Vitamin B12: Fact Sheet for Health Professionals. 2025.
- NIH Office of Dietary Supplements. Vitamin B12: Fact Sheet for Consumers. 2023.
- MedlinePlus Medical Encyclopedia. Vitamin B12 deficiency anemia. National Library of Medicine. 2025.
- MedlinePlus Medical Encyclopedia. Vitamin B12 level. National Library of Medicine.
- Green R, Allen LH, Bjørke-Monsen AL, et al. Vitamin B12 deficiency. Nat Rev Dis Primers. 2017.
- Wang H, Li L, Qin LL, et al. Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency. Cochrane Database Syst Rev. 2018.
- Aroda VR, Edelstein SL, Goldberg RB, et al. Long-term Metformin Use and Vitamin B12 Deficiency in the Diabetes Prevention Program Outcomes Study. J Clin Endocrinol Metab. 2016.
- Lam JR, Schneider JL, Zhao W, Corley DA. Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency. JAMA. 2013.
Disclosure: OPA Nutrition sells supplements, including products mentioned in this article. This content is for education only and is not medical advice. Statements about dietary supplements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Talk to your healthcare provider before using any supplement, especially if you take medication or have a medical condition.
Written and reviewed by Michael Gonzales, Founder, OPA Nutrition · Last reviewed: · How OPA researches and writes
