Vitamin B12 sources and how well the body absorbs it
What it found
Vitamin B12 comes mainly from animal foods, and how much the body takes in drops as the amount in a meal goes up.
In people, fish, sheep and chicken meat gave different amounts, and eggs gave the least.
What they found
Studies in people
Absorption drops with dose
The gut system that takes in vitamin B12 is thought to be full at about 1.5 to 2.0 micrograms per meal. So the share the body takes in falls as the amount in a meal rises.
How much from meats
In healthy people, the share of vitamin B12 taken in averaged 42% from fish, 56% to 89% from sheep meat, and 61% to 66% from chicken.
Eggs poorly absorbed
Vitamin B12 in eggs appears to be taken in poorly, at less than 9%, compared with other animal foods.
Other findings
Main food sources
The usual places vitamin B12 comes from in the diet are animal foods: meat, milk, egg, fish and shellfish.
Official intake assumption
US and Japanese dietary reference intakes assume healthy adults with normal gut function take in 50% of the vitamin B12 in their diet.
Plant foods and algae
Some plant foods, dried green and purple lavers (nori), hold substantial amounts of vitamin B12, but other edible algae had none or only traces. Most edible blue-green algae used in human supplements mainly contain pseudovitamin B12, which is inactive in people.
Fortified cereals and vegetables
Fortified breakfast cereals are a particularly valuable source of vitamin B12 for vegans and elderly people. Work is also being done to produce some vitamin B12-enriched vegetables.
What the authors conclude
- They say the edible cyanobacteria are not suitable for use as vitamin B12 sources, especially in vegans.
- They note that fortified breakfast cereals are a particularly valuable source of vitamin B12 for vegans and elderly people.
What it can’t tell you
- We summarised it from the abstract only.
- This paper pulls together findings from other work rather than running its own study.
- It cannot show how vitamin B12 from a specific product on a shelf will be taken in by any one person.
Who paid
- Authors work at
- Tottori University, Japan
The paper
- Title
- Vitamin B12 sources and bioavailability
- Type
- ReviewThe authors read earlier studies and describe what they found. It isn’t a new study.
- Evidence
- Studies in people
- Summarised from
- Abstract only
- Cite
- Watanabe F (2007). Vitamin B12 sources and bioavailability. Experimental biology and medicine (Maywood, N.J.). doi:10.3181/0703-MR-67PubMed 17959839DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error