Vitamin B12: what it does, how much you need, and how much is too much
By Vita · fact-checked against NIH ODS
Vita is Vitaminico's AI nutrition coach. Every number here is checked against the NIH Office of Dietary Supplements; these pages have not yet been reviewed by our registered dietitians.
A vitamin that keeps your blood and nerve cells healthy and helps make DNA.
Vitamin B12: key facts
- Everyday need (RDA/AI)
- 2.4 mcg for all adults (2.6 mcg in pregnancy, 2.8 mcg in lactation)
- Safe upper limit (UL)
- No established UL
- Measured in
- mcg
- Best foods
- Beef liver, clams, fish, meat, poultry, eggs, dairy products
Adult values from the NIH ODS Vitamin B12 fact sheet. Needs differ in pregnancy, lactation and childhood.
What does vitamin b12 do?
Vitamin B12 helps keep your body's blood and nerve cells healthy and helps make DNA, the genetic material in all your cells. It also helps prevent megaloblastic anemia, a blood condition that leaves people tired and weak. Your body absorbs it from food in two steps: stomach acid frees the B12 from protein, then it binds to a stomach protein called intrinsic factor so it can be taken up.
Why you might be low on vitamin b12
- You eat little or no animal food — only animal foods naturally contain B12, so vegetarians and vegans (and the breastfed babies of vegan mothers) can fall short
- You're over 50 — many older adults make too little stomach acid to release B12 from food, so guidance is to get most B12 from fortified foods or supplements
- You have pernicious anemia or atrophic gastritis — your stomach can't make enough intrinsic factor or acid to absorb B12
- You've had stomach or intestinal surgery (such as weight-loss or gastric surgery), or have celiac or Crohn's disease, which impair absorption
- You take a gastric acid reducer (omeprazole, lansoprazole, cimetidine, ranitidine) or metformin, which can lower B12 absorption or blood levels
Signs of low vitamin b12
These are common signals, not a diagnosis — a blood test and your clinician confirm a real gap.
- Tiredness or weakness (from megaloblastic anemia, the hallmark of B12 deficiency)
- Numbness or tingling in the hands and feet, a sign of nerve problems
- Pale skin, heart palpitations, loss of appetite, and weight loss
- Problems with balance
- Depression, confusion, poor memory, or dementia
- Soreness of the mouth or tongue
Best food sources of vitamin b12
| Food | Typical amount |
|---|---|
| Beef liver, cooked, pan fried | 70.7 mcg per 3 oz |
| Clams, cooked (without shells) | 17 mcg per 3 oz |
| Salmon, Atlantic, cooked | 2.6 mcg per 3 oz |
| Ground beef, 85% lean, pan browned | 2.4 mcg per 3 oz |
| Milk, 2% milkfat | 1.3 mcg per 1 cup |
| Fortified breakfast cereal (25% DV) | 0.6 mcg per serving |
| Egg, whole, cooked | 0.5 mcg per 1 large egg |
How much vitamin b12 is too much?
Vitamin B12 has no established upper limit. No UL because excess is considered safe even at high doses; deficiency (common in vegans and older adults) can cause anemia and nerve damage.
Vitamin B12 has no established upper limit — the Food and Nutrition Board didn't set one because it has a low potential for toxicity and hasn't been shown to cause harm even at high doses. Even large supplement doses like 500 or 1,000 mcg are considered safe, since your body absorbs only a small fraction and doesn't store the excess.
Stacking a multivitamin, a single supplement and fortified foods adds up faster than it looks — run your full dose through the free Supplement Safety Checker before adding anything new.
Vitamin B12 FAQ
Will B12 supplements give me more energy?
Not if you already get enough from your diet. Despite the marketing, B12 doesn't boost energy, athletic performance, or endurance in people who aren't deficient.
I'm vegan — do I need to worry about B12?
Yes. Only animal foods naturally contain B12, so vegans and vegetarians should get it from fortified foods (like some cereals and nutritional yeasts) or a supplement. Vegan mothers who are pregnant or breastfeeding should be especially careful, since their babies can also come up short.
Is one form of B12 supplement better than another?
Research hasn't shown any form to be superior. Cyanocobalamin, methylcobalamin, adenosylcobalamin, hydroxocobalamin, and sublingual (under-the-tongue) versions all work; the body absorbs only a small percentage of any high dose.
Source
Every RDA/AI, upper limit and unit on this page is drawn from the NIH Office of Dietary Supplements Vitamin B12 fact sheet ›.
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Educational, not medical advice. The upper limits shown are Tolerable Upper Intake Levels for healthy adults from all sources combined; needs differ in pregnancy, lactation, childhood and with some conditions or medications. This page does not diagnose a deficiency or set your dose — talk to your clinician before starting any high-dose supplement.