Vitamin B12 deficiency, its causes and effects on the body
What it found
Vitamin B12 shortage can affect the blood, bone marrow and nervous system in people of all ages.
The body needs it for only two chemical reactions, but both are essential.
What they found
Studies in people
How the body uses B12
People need less vitamin B12 each day than any other water-soluble vitamin. The body uses it for just two chemical reactions, one inside cells and one in the energy-making parts of cells.
Causes of shortage
A shortage can happen when the gut cannot absorb the vitamin properly or when someone does not eat enough of it. Problems with the stomach or the end of the small intestine can block absorption.
Effects on blood
A lack of vitamin B12 stops fast-growing cells from making DNA properly. This leads to a type of anemia where red blood cells grow too large.
Effects on the brain
Shortages can damage the protective coating around nerves. People may also experience memory problems or psychosis.
Who is most affected
Older people more often have trouble absorbing the vitamin. But shortages happen at every age, especially where people struggle to get enough food.
What the authors conclude
- They explain that diagnosing a shortage relies on doctors suspecting it first and then using a set of lab tests together.
- They note that vitamin B12 works closely with folate, another B vitamin, so the two are linked in the body.
How it was done
The authors wrote this overview because vitamin B12 has a complicated path through the body and many things can go wrong with it. They wanted to explain how a shortage happens and what it does to people.
This is an educational chapter rather than a new experiment. The authors gathered existing knowledge about how the body uses vitamin B12, what causes a shortage and how doctors test for it. They did not recruit patients or run trials.
What it can’t tell you
- We summarised it from the abstract only.
- This is a summary of existing knowledge, not a trial testing a treatment. It cannot show whether taking extra vitamin B12 prevents these problems in any specific person.
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 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error