Vitamin B12 absorption and malabsorption in the body
What it found
Vitamin B12 is taken in and moved around the body by a complex system of carrier proteins and receptors.
Many digestive diseases and inherited conditions can stop this process from working properly.
What they found
Studies in people
Checking B12 after surgery
The authors recommend checking for B12 deficiency during follow-up of people who have had bariatric surgery.
Other findings
How B12 is absorbed
In the stomach, B12 is released from food proteins and binds to a protein called haptocorrin. In the small intestine, haptocorrin is broken down and B12 transfers to intrinsic factor, which then helps it be taken up in the lower part of the small intestine.
B12 recycling
Some B12 stored in the liver is sent out in bile and then reabsorbed, going through a loop between the liver and the gut.
Causes of malabsorption
The main causes of poor B12 absorption include inherited conditions such as intrinsic factor deficiency, Imerslund-Gräsbeck disease, Addison's pernicious anemia, obesity, bariatric surgery and gastrectomies. Other causes include pancreatic insufficiency, obstructive jaundice, tropical sprue, celiac disease, bacterial overgrowth, parasitic infestations, Zollinger-Ellison syndrome, inflammatory bowel diseases, chronic radiation enteritis of the distal ileum and short bowel.
Genetic causes underestimated
The genetic causes of B12 malabsorption are probably underestimated in adults with B12 deficiency.
Testing problem
B12 malabsorption is common in the general population and in the elderly, but it can no longer be assessed with the Schilling test. There is an urgent need for an equivalent reliable test.
What the authors conclude
- They recommend assessing B12 deficit in the follow-up of subjects with bariatric surgery.
- They say the genetic causes of B12 malabsorption are probably underestimated in adult cases with B12 deficit.
- They point out the urgent need for an equivalent reliable test because B12 malabsorption cannot be anymore assessed by the Schilling test.
How it was done
Vitamin B12 deficiency is mainly caused by not getting enough in the diet, especially in vegans, and by problems absorbing it because of digestive diseases. The authors wanted to explain how B12 is normally absorbed and what goes wrong in malabsorption.
What it can’t tell you
- We summarised it from the abstract only.
- This is a review of how B12 is absorbed and what can go wrong. It does not test treatments or compare groups of people.
- It cannot show how common each cause of malabsorption is, or which test might replace the Schilling test.
Who paid
- Authors work at
- University of Lorraine, France; University Hospital of Nancy, France; Washington University School of Medicine, United States
The paper
- Title
- Vitamin B12 absorption and malabsorption
- 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
- Guéant JL, Guéant-Rodriguez RM, Alpers DH (2022). Vitamin B12 absorption and malabsorption. Vitamins and hormones. doi:10.1016/bs.vh.2022.01.016PubMed 35337622DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error