Vitamin B12
Also known as Cobalamin
Vitamin B12, also called cobalamin, is a water-soluble vitamin required for red blood cell formation, DNA synthesis, and normal nerve function. It occurs naturally only in animal foods and in fortified products. Absorption depends on stomach acid and intrinsic factor, so many older adults and people with certain conditions absorb it poorly even when intake is adequate.
Why it matters
What it does in your body
- Serves as a cofactor for DNA synthesis and red blood cell formation
- Maintains the myelin sheath and healthy nerve function
- Works with folate to convert homocysteine to methionine
- Supports normal brain function and energy metabolism
- Required for proper cell division
By age, sex, and life stage
How much you need
Infant values are Adequate Intakes (AI); values for ages 1 and older are RDAs. Many older adults have reduced stomach acid or intrinsic factor and absorb naturally occurring B12 poorly, so they are advised to get much of their B12 from fortified foods or supplements, which are more easily absorbed.
Recommended intake across life
in mcg/dayBars scale to the highest recommendation shown. Where men and women differ, both values are listed.
Full reference table
| Life stage | Male | Female |
|---|---|---|
| Infants 0-6 mo | 0.4 (AI) | 0.4 (AI) |
| Infants 7-12 mo | 0.5 (AI) | 0.5 (AI) |
| Children 1-3 | 0.9 | 0.9 |
| Children 4-8 | 1.2 | 1.2 |
| Children 9-13 | 1.8 | 1.8 |
| Teens 14-18 | 2.4 | 2.4 |
| Adults 19+ | 2.4 | 2.4 |
| Pregnancy | n/a | 2.6 |
| Lactation | n/a | 2.8 |
Values in mcg/day. AI marks an Adequate Intake, used when there is not enough evidence for a formal recommendation.
What moves the number
What changes your needs
Age
Older adults commonly have reduced stomach acid, which impairs absorption of B12 from food; a notable share of older adults may be deficient.
Sex
The RDA is the same for adult men and women, 2.4 mcg per day, outside of pregnancy and lactation.
Body weight / size
Requirements are set per person rather than by body weight; the small daily need reflects efficient recycling of B12 through bile.
Pregnancy and lactation
Needs rise to 2.6 mcg during pregnancy and 2.8 mcg during lactation; infants of vegan mothers with low B12 are at risk of severe deficiency.
Absorption
Absorption requires stomach acid and intrinsic factor. Pernicious anemia, gastric or ileal surgery, celiac and Crohn's disease, and long-term use of metformin or acid-reducing drugs all reduce absorption.
Running low
Signs you might not get enough
Most at risk: Older adults with reduced stomach acid, people with pernicious anemia, those with gastrointestinal disorders or after gastric bypass surgery, and vegetarians and vegans, along with breastfed infants of vegan mothers.
Too much
Can you get too much?
Vitamin B12 has not been shown to cause harm even at high intakes, and the body stores or excretes excess amounts, so no upper limit has been established.
Where to get it
Best food sources
The bottom line
Vitamin B12 keeps blood and nerve cells healthy and helps make DNA. It is found naturally only in animal foods, so vegans and vegetarians need fortified foods or supplements. Because absorption declines with age, adults over 50 are advised to get much of their B12 from fortified foods or supplements.
Track vitamin b12 automatically
Vitamin B12 is one of the 92 nutrients Vora reads from a photo of your meal, so you can see where you stand without weighing or logging by hand.
Sources and method
The recommended intakes, upper limits, and food-source amounts on this page come from the primary references below. Numbers were checked against the current NIH Office of Dietary Supplements fact sheets and the Institute of Medicine (now the National Academies) Dietary Reference Intakes.
- NIH Office of Dietary Supplements, Vitamin B12 Fact Sheet for Health Professionals
- Institute of Medicine (IOM/NASEM), Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline
This page is for general education, not medical advice. Reference intakes are population averages for healthy people and do not replace guidance from your doctor or a registered dietitian, especially if you are pregnant, managing a health condition, or considering supplements.