A nutrient that's mostly animal-based
Vitamin B12 is unusual among vitamins in that it comes almost entirely from animal foods [1]. That single fact drives most B12 advice: people who eat animal products usually get enough, while those who don't must plan for it.
Food sources
- Richest: clams, beef liver, fish (salmon, trout, tuna), and shellfish.
- Common: meat, poultry, eggs, milk, yogurt, and cheese.
- Fortified: many breakfast cereals and nutritional yeast are fortified with B12 — important for plant-based eaters.
The adult RDA is 2.4 mcg/day (slightly more in pregnancy and lactation) [1].
Who's at risk of falling short
- Vegans and many vegetarians, since plant foods don't reliably provide B12 — see [supplements for vegans](/learn/supplements-for-vegans).
- Older adults, who absorb food-bound B12 less efficiently as stomach acid declines.
- People on long-term acid reducers or metformin, which can lower B12 (see [nutrient depletion from medications](/learn/nutrient-depletion-from-medications)).
- People with absorption conditions or gut surgery.
Why supplements work well here
Unlike food B12 (which needs stomach acid to be released), B12 in supplements and fortified foods is in free form and reliably absorbed [1]. So for at-risk groups, a supplement or fortified foods are a dependable solution. There's no upper limit for B12 because high intakes haven't shown toxicity (see why some nutrients have no upper limit).
Practical guidance
- Animal-food eaters usually meet B12 needs without trying.
- Vegans/vegetarians should use fortified foods and/or a B12 supplement reliably.
- Older adults and those on acid reducers/metformin should ask about checking B12.
- Note the separate caution that high folic acid can [mask a B12 deficiency](/learn/folate-intake-and-b12-masking).