SupplementsVitaminsVitamin B12
Vitamin B12
as methylcobalamin
A vitamin your body can store for years, which is exactly why a shortage can creep up without you noticing.
- Builds up
- Weeks to months
- In your body
- Stored for years
- Per 1 capsule
- 1000 mcg
- 30-day supply
- $3.60One capsule a day, plus packing and delivery
What is vitamin b12?
Vitamin B12 helps your body make red blood cells, look after your nerves and build DNA. Plants don't make it, so it comes from fish, meat, eggs, milk and fortified foods.
You only need a tiny amount: 2.4 mcg a day for adults. Your body's way of absorbing it is complicated, though. Your stomach has to free it from food and make a protein called intrinsic factor, which carries it into your gut. Anything that disturbs that process can leave you short, even if you eat plenty.
Ours is methylcobalamin, one of the active forms of B12, in a vegan capsule. It's colored with beet juice.
What it does
- Red blood cellsSupports the normal formation of red blood cells.
- NervesSupports normal nerve function and the nervous system.
- EnergyHelps your body's normal energy production, and reduces tiredness when you're low.
- MethylationSupports normal homocysteine metabolism alongside folate.
These statements have not been evaluated by the FDA. This product is not intended to diagnose, treat, cure or prevent any disease.
What people take it for
Good evidenceVegan and vegetarian dietsThe clearest reason. Studies keep finding low B12 in people who skip animal foods, more so in vegans.
Good evidenceOlder age and common medicinesAbsorption often drops with age, and metformin and acid reducers can lower it too.
MixedEnergy and focusIf you're low, this can make a real difference. If you aren't, it's unclear whether extra gives you more energy.
How long it takes
Levels rise over weeks, and symptoms can take longer. Studies on oral B12 ran for 3 to 4 months. If your nerves are affected, recovery can be slower.
- HoursA small part of each capsule is absorbed, and extra leaves in your urine
- 3 to 5 weeksWhen symptoms began to ease in some reported cases on B12 shots, though recovery varies
- YearsHow long your stores can last, and how long a shortage can take to appear
How long it stays in your body
Your liver holds on to B12 for a long time, and your body recycles it carefully. That's why a shortage can take years to show, even after your intake drops.
What's in a capsule
One capsule holds 1,000 mcg, far more than the 2.4 mcg a day you need. That's on purpose, because only a small part of a big amount gets in. Studies comparing pills with injections used 1,000 to 2,000 mcg a day.
Why a normal result doesn't always mean you're fine
A standard B12 blood test isn't perfect. Doctors have documented plenty of people with real symptoms and a result inside the normal range. So when it matters, they add methylmalonic acid and homocysteine, which rise when your cells don't have enough B12. Numbness, tingling and balance problems with a normal-looking result are worth pushing on.
Folate adds a twist. High amounts of folate can hide the anemia that B12 shortage causes, while nerve damage keeps going. That's why you should test both, rather than assuming.
Which form of B12 works best, and whether high-dose capsules can match shots, is in the full guide.
What it interacts with
- MetforminIt lowers B12 over time. After 5 years, about 19% of people on it had low or borderline levels, compared with about 10% on a dummy pill. Worth testing.
- Acid-reducing medicines (PPIs, H2 blockers)Taking them for 2 years or more is linked to a higher chance of low B12, because stomach acid helps free it from food.
- Nitrous oxideThis gas, used in dentistry and recreationally, can disrupt B12 and cause problems even with a normal-looking result. Tell your doctor if you've been exposed.
- Cancer treatmentOne study linked B12 use before and during chemotherapy for breast cancer with poorer survival. It doesn't prove cause, but tell your oncologist.
- Diabetic kidney diseaseIn one study, B12 at this same 1,000 mcg, given with folic acid and B6, went with faster kidney decline and more heart and blood vessel events. Ask your doctor.
Goes well with
Side effects
- Usually none. Oral B12 has been well tolerated in the small studies that looked, though they were too small to catch rare problems.
Check first if
- Numbness, tingling or balance problems: see a doctor rather than just taking a capsule, because nerve damage needs proper follow-up.
- Diabetic kidney disease: ask your doctor first.
- Cancer treatment: tell your oncologist first.
- Allergy to cobalt or cobalamin, Leber's hereditary optic neuropathy, or kidney disease: tell your doctor before taking B12.
- Pregnancy or breastfeeding: your needs are a little higher, so ask what's right for you.
The blood tests that go with it
- Vitamin B12The usual first test, though it can look normal when your cells are low.
- Methylmalonic acidRises when your cells are short of B12. Kidney problems can raise it too.
- HomocysteineRises with low B12, folate or B6.
- HolotranscobalaminMeasures the B12 your cells can actually use.
- MCVRed blood cell size, which goes up with low B12.
- HemoglobinFalls when low B12 causes anemia.
Supplementation
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These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure or prevent any disease.
Want it more precise? Get the app.
A page can only tell you about Vitamin B12. The app tells you about you: whether it fits, when to take it, and whether it's working.
- Checked against your blood work and everything you already take
- On your daily timeline, around your sleep, training and meals
- Followed over time, so you can see what moved
Vitamin B12OPEN 09:00Vitamin B12 against your blood work, your sleep and what you already take.
AIYou've been on metformin for 4 years and your last B12 was borderline. Worth adding methylmalonic acid to your next test?
ASK ABOUT VITAMIN B12Find the goal that's yours.
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Questions
What is vitamin B12 good for?
Making red blood cells, keeping your nerves working and producing DNA. Most people notice it only when they run low.
What are the benefits of vitamin B12?
If you're low, it can lift tiredness and support your nerves and blood. If your level's already fine, it's unclear whether extra adds energy.
How long does vitamin B12 take to work?
Blood levels rise over weeks. In some reported cases, on shots, symptoms began to ease in about 3 to 5 weeks. Recovery varies from person to person, and nerve problems can take longer.
What are the side effects of vitamin B12?
Usually none. Oral B12 appears well tolerated, though the studies were small. Certain people, such as those with diabetic kidney disease, should ask first.
Can you take too much B12?
There's no official upper limit, because your body absorbs only a small part and it's generally considered safe. Still, high amounts haven't been harmless for everyone, like some people with diabetic kidney disease.
What are the signs of low B12?
Tiredness, anemia, numbness or tingling in the hands and feet, weakness, loss of balance and memory problems. See a doctor if you notice these.
Who tends to run low on vitamin B12?
Mostly vegans and vegetarians, older adults, people on metformin or long-term acid reducers, and anyone who has had stomach surgery. A blood test helps.
Can I take B12 every day?
Yes, that's how it was taken in studies comparing it with shots. Check first if you have diabetic kidney disease or are having cancer treatment.
Sources
- MedlinePlus. Vitamin B12.
- MedlinePlus. Cyanocobalamin injection.
- Wolffenbuttel BHR et al. The many faces of cobalamin (vitamin B12) deficiency. Mayo Clin Proc Innov Qual Outcomes, 2019.
- Carmel R. How I treat cobalamin (vitamin B12) deficiency. Blood, 2008.
- Green R et al. Vitamin B12 deficiency. Nat Rev Dis Primers, 2017.
- Wang H et al. Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency. Cochrane Database Syst Rev, 2018.
- Obeid R et al. Cobalamin coenzyme forms are not likely to be superior to cyano- and hydroxyl-cobalamin in prevention or treatment of cobalamin deficiency. Mol Nutr Food Res, 2015.
- Aroda VR et al. Long-term metformin use and vitamin B12 deficiency in the Diabetes Prevention Program Outcomes Study. J Clin Endocrinol Metab, 2016.
- Lam JR et al. Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency. JAMA, 2013.
- Allen LH. How common is vitamin B-12 deficiency? Am J Clin Nutr, 2009.
- Pawlak R et al. How prevalent is vitamin B12 deficiency among vegetarians? Nutr Rev, 2013.
- House AA et al. Effect of B-vitamin therapy on progression of diabetic nephropathy. JAMA, 2010.
- Ambrosone CB et al. Dietary supplement use during chemotherapy and survival outcomes of patients with breast cancer. J Clin Oncol, 2020.
- Agostinho et al. Acute psychosis and dissociative syndrome following binge recreational nitrous oxide use: a case report. Cureus, 2026.
- NIH Office of Dietary Supplements. Vitamin B12: fact sheet for health professionals.
Written by LifeFrom from these sources, and not yet reviewed by a clinician. Talk to your doctor before starting a supplement.
