How vitamin B12 is absorbed and why absorption sometimes fails
What it found
Vitamin B12 relies on three transport proteins and specific gut receptors to be taken in by the body.
Digestive diseases, weight-loss surgery, and inherited conditions can all block this process.
What they found
Studies in people
Dietary lack in vegans
A shortage of vitamin B12 mostly happens when people do not eat enough of it. This is mainly seen in vegans.
Surgery and malabsorption
Weight-loss surgery and stomach removals are major causes of B12 malabsorption. The authors recommend checking B12 levels in people who have had weight-loss surgery.
Genetic causes overlooked
Inherited conditions that block B12 absorption are likely missed in adults who show low B12 levels.
Other findings
How B12 travels
In the stomach, B12 separates from food and binds to a protein called haptocorrin. In the small intestine, it transfers to another protein called intrinsic factor before being taken up by gut cells.
Liver recycling of B12
Some B12 stored in the liver is released into bile. It then travels back through the gut to be taken up again.
Need for better tests
B12 malabsorption is common, especially in older people. The old test used to check for it is no longer available, so a reliable replacement is urgently needed.
What the authors conclude
- They recommend checking B12 levels regularly in people who have had weight-loss surgery.
- They suggest that doctors may be overlooking genetic reasons for low B12 in adults.
- They call for a new, reliable test to replace the one that is no longer used.
How it was done
The authors wanted to explain how the body takes in vitamin B12 and what conditions stop that from happening properly.
They gathered and examined existing research on how vitamin B12 moves through the digestive system. They also looked at the diseases and conditions that prevent proper absorption.
What it can’t tell you
- We summarised it from the abstract only.
- This work gathers past research rather than testing people directly. It cannot prove which cause of malabsorption is most common in everyday life.
- Because it looks at many different conditions together, it cannot show exactly how much each one lowers B12 levels in a single person.
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 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error