Quick answer
Adults need 2.4 mcg of vitamin B12 a day, 2.6 mcg in pregnancy and 2.8 mcg while breastfeeding, the same for men and women. Supplements usually hold 5 to 1,000 mcg, because only a small share of a large dose is absorbed. No upper limit is set.1,2
Key facts
- There is no separate amount for people over 70; the adult figure of 2.4 mcg applies.2
- From food alone, US women average 3.69 mcg of B12 a day and men 5.84 mcg.2
- B12 from supplements is absorbed about 50% better than B12 from food.2
- US adults who take a B12 supplement average 297 mcg a day in total if men and 407 mcg if women.2
Recommended amounts by age
| Age or stage | Recommended per day |
|---|---|
| Birth to 6 months | 0.4 mcg |
| 7 to 12 months | 0.5 mcg |
| 1 to 3 years | 0.9 mcg |
| 4 to 8 years | 1.2 mcg |
| 9 to 13 years | 1.8 mcg |
| 14 years and over | 2.4 mcg |
| Pregnancy | 2.6 mcg |
| Breastfeeding | 2.8 mcg |
Men and women have the same recommendation, and it does not rise with age after 14. The adult figure was set as the intake that keeps blood counts and blood B12 levels normal.2
Why supplement doses are so much higher
About 50% of a B12 dose is absorbed at 1 to 2 mcg or less, but only about 2% of a 500 mcg dose and 1.3% of a 1,000 mcg dose.2
Intrinsic factor, the main route for absorbing B12, is saturated at about 1.5 to 2 mcg per meal, so the share absorbed falls as the amount taken at one time rises.2,3
| Dose | Share absorbed | Amount absorbed |
|---|---|---|
| 1 to 2 mcg | About 50% | About 0.5 to 1 mcg |
| 500 mcg | About 2% | About 10 mcg |
| 1,000 mcg | About 1.3% | About 13 mcg |
Multivitamins usually contain 5 to 25 mcg of B12, B-complex products 50 to 500 mcg, and supplements with only B12 typically 500 to 1,000 mcg.2
Over 50, over 70
The recommended amount stays at 2.4 mcg a day after 50, but NIH advises getting most of it from fortified foods or supplements, because in most cases people that age can absorb B12 from those sources.1
Many older adults make too little stomach acid to free B12 from food protein, which is why the advice shifts toward fortified foods and supplements rather than to a bigger number.1
When older adults already have mildly low B12, far more is used. In a 16-week trial in 120 people, 647 to 1,032 mcg a day of oral cyanocobalamin was needed to bring methylmalonic acid, a marker of shortage, most of the way down, while 2.5 to 250 mcg a day did much less. That trial was in people whose low levels had been found by testing, so it says nothing about what people with normal levels need.4
Is 2.4 mcg enough?
A systematic review estimated that healthy adults and older people lose 1.4 to 5.1 mcg of B12 a day, and that replacing it would take 3.8 to 20.7 mcg a day from food.5
Those estimates run higher than the official figure, and the review's authors asked for more evidence before any change. The US recommendation remains 2.4 mcg a day for adults.1,5
If you eat little or no animal food
Vegans need B12 from fortified foods or supplements. In a 90-day trial of vegans and vegetarians with marginal levels, 50 mcg a day under the tongue was enough to bring blood B12 back to adequate levels.2,6
When higher doses are used
No upper limit is set for vitamin B12 because it has a low potential for harm. NIH says it is generally considered safe even at large doses, such as 500 or 1,000 mcg, because the body does not store the excess.1,2
Doses of 1,000 to 2,000 mcg a day by mouth are used under medical care to raise low levels, as an alternative to injections. If you think you are low, get tested before choosing a dose, because people who cannot absorb B12, such as those with pernicious anemia, may need shots.1,7
- Ask first if you take metformin or a medicine that reduces stomach acid
- Ask first if you have numbness, tingling or balance problems, which need testing
Questions people ask
Is 1,000 mcg of B12 a day too much?
No upper limit is set, and NIH says doses of 500 or 1,000 mcg are considered safe. Only about 1.3% of a 1,000 mcg dose is absorbed.1,2
How much B12 should a woman over 50 take?
The same 2.4 mcg a day as other adults, mostly from fortified foods or a supplement, as NIH advises for everyone over 50. A doctor may advise more if a blood test shows a low level.1
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Sources
- National Institutes of Health, Office of Dietary Supplements. Vitamin B12: Fact Sheet for Consumers. Updated December 15, 2023. Opened 2026-10-07.
- National Institutes of Health, Office of Dietary Supplements. Vitamin B12: Fact Sheet for Health Professionals. Updated July 2, 2025. Opened 2026-10-07.
- Watanabe F. Vitamin B12 sources and bioavailability. Exp Biol Med (Maywood). 2007;232(10):1266-1274. Opened 2026-10-07.
- Eussen SJ, de Groot LC, Clarke R, et al. Oral cyanocobalamin supplementation in older people with vitamin B12 deficiency: a dose-finding trial. Arch Intern Med. 2005;165(10):1167-1172. Opened 2026-10-07.
- Doets EL, In 't Veld PH, Szczecińska A, et al. Systematic review on daily vitamin B12 losses and bioavailability for deriving recommendations on vitamin B12 intake with the factorial approach. Ann Nutr Metab. 2013;62(4):311-322. Opened 2026-10-07.
- Del Bo' C, Riso P, Gardana C, et al. Effect of two different sublingual dosages of vitamin B12 on cobalamin nutritional status in vegans and vegetarians with a marginal deficiency: a randomized controlled trial. Clin Nutr. 2019;38(2):575-583. Opened 2026-10-07.
- Wang H, Li L, Qin LL, et al. Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency. Cochrane Database Syst Rev. 2018;3(3):CD004655. Opened 2026-10-07.
This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.