Vitamin B12 deficiency and its effects on the body
What it found
Vitamin B12 deficiency can affect the blood, bone marrow and nervous system, and is more common with age but occurs in all age groups, especially where food insecurity happens.
What they found
Studies in people
Who is affected
B12 deficiency is more common with advancing age because of higher rates of malabsorptive disorders in the elderly. It is widely distributed across all age groups, particularly where food insecurity occurs.
Consequences and severity
The consequences and severity of B12 deficiency vary depending on the degree of deficiency and its duration. Major organ systems affected include the blood, bone marrow and nervous system.
Blood and nervous system effects
Megaloblastic anemia results from a defect in thymidine and therefore DNA synthesis in rapidly dividing cells. Nervous system involvement is varied, some of which results from defective myelin synthesis and repair. Cognitive impairment and psychosis may also occur.
Other findings
Low daily requirement
Vitamin B12 has the lowest daily requirement of all the water-soluble vitamins.
Complex absorption
Vitamin B12 needs a complex pathway for absorption and assimilation. This requires intact stomach and terminal small intestinal function, an enterohepatic pathway, and several dedicated binding proteins and chaperons.
Causes of deficiency
The many causes of B12 deficiency include malabsorption, defects in cellular delivery and uptake, and limited dietary intake.
Two reactions in humans
B12 is required as a cofactor for only two reactions in humans: the cytosolic methionine synthase reaction and the mitochondrial methylmalonyl CoA mutase reaction. Disruption of either reaction gives rise to B12 deficiency.
Diagnosis
Diagnosis of B12 deficiency rests on clinical suspicion followed by laboratory testing. This consists of a panel of tests that together provide clinically reliable predictive indices.
Link with folate
B12 metabolism and deficiency is closely intertwined with folate, another B-vitamin.
What the authors conclude
- They state that this chapter explores the various aspects of a unique and fascinating micronutrient.
How it was done
The authors wanted to explore the unique properties of vitamin B12, including its complex absorption pathway and the many causes of deficiency.
What it can’t tell you
- We summarised it from the abstract only.
- This paper does not report on a new study in people or animals. It is a summary of existing knowledge.
- It cannot show cause and effect for any specific treatment or dose.
Who paid
- Authors work at
- University of California Davis Medical Center, United States; Rutgers University, United States
The paper
- Title
- Vitamin B12 deficiency
- Type
- Study
- Evidence
- Studies in people
- Summarised from
- Abstract only
- Cite
- Green R, Miller JW (2022). Vitamin B12 deficiency. Vitamins and hormones. doi:10.1016/bs.vh.2022.02.003PubMed 35337628DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error