Natural Medical SolutionsVitamin B12 keeps your blood and nerve cells healthy and helps your body make DNA. It also helps prevent a type of anemia that leaves people tired and weak.
What does vitamin B12 do?
Vitamin B12 is a nutrient with a few important jobs:
- Keeps your blood cells healthy
- Keeps your nerve cells healthy
- Helps make DNA, the genetic material in every cell
- Helps prevent megaloblastic anemia, which makes people tired and weak
How much vitamin B12 do you need?
It depends on your age. The average daily recommended amounts are:
- Adults: 2.4 micrograms
- Pregnant teens and women: 2.6 micrograms
- Breastfeeding teens and women: 2.8 micrograms
- Teens 14 to 18: 2.4 micrograms
- Children 9 to 13: 1.8 micrograms
- Children 4 to 8: 1.2 micrograms
- Children 1 to 3: 0.9 micrograms
These are small numbers. Micrograms, not milligrams.
Can you take too much vitamin B12?
Vitamin B12 has not been shown to cause any harm, even at high doses.
That is unusual among vitamins, and it is worth saying plainly. There is no upper limit set for it.
It does not mean a high dose is useful. It means a high dose has not been shown to hurt you.
Who should watch their B12 level?
Some medicines lower your B12, so tell your doctor if you take:
- Metformin, for prediabetes or diabetes
- Acid reflux or ulcer medicines, especially long term. These include omeprazole (Prilosec), lansoprazole (Prevacid), cimetidine (Tagamet) and ranitidine (Zantac).
Both are very common, and both are usually taken for years rather than weeks. That is what makes them worth knowing about.
Does Vitamin B12 interact with any medications?
Talk to your doctor and pharmacist before taking vitamin b12 if you take any prescription medicine. The list below is not complete.
Metformin might reduce how much vitamin B12 you absorb, and lower the level of B12 in your blood. If you take metformin, ask your doctor whether your B12 should be checked.
These slow the release of stomach acid, and your body needs that acid to pull B12 out of food. Taken long term they can lead to B12 deficiency.
Common questions about vitamin b12
Does metformin lower vitamin B12?
Can you take too much vitamin B12?
Do acid reflux medicines affect B12?
How much vitamin B12 do adults need?
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Where this information comes from
Written from NIH Office of Dietary Supplements, a public-domain resource from the U.S. National Institutes of Health. Information retrieved 2026-08-21.
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