What is Vitamin B12?
Vitamin B12, also known as cobalamin, is a water-soluble vitamin that is essential for the body but cannot be produced by it. It is the only vitamin that contains cobalt — a mineral from which its name derives. B12 is found primarily in animal-based foods: meat, fish, eggs and dairy products.
B12 deficiency can develop slowly and manifest as fatigue (Green et al., 2017), weakness and difficulty concentrating. Vegans, older adults and those with digestive issues are particularly at risk.
How does Vitamin B12 work?
B12 acts as a coenzyme in two important biochemical reactions. First, it participates in methionine synthesis (Stabler, 2013), which is necessary for DNA methylation and homocysteine metabolism. Second, B12 is required for methylmalonyl-CoA mutase function, which is important for the breakdown of fatty acids and amino acids.
B12 absorption is a complex process. In the stomach, B12 is released from food, binds to intrinsic factor (IF) — a protein produced by stomach cells — and is absorbed in the terminal ileum. This is why stomach conditions or surgeries can impair absorption.
Evidence and benefits
The European Food Safety Authority (EFSA) has approved the following health claims for vitamin B12:
- Contributes to normal energy-yielding metabolism — B12 participates in cellular energy production
- Contributes to normal functioning of the nervous system — essential for myelin sheath formation and maintenance
- Contributes to normal red blood cell formation — deficiency can cause megaloblastic anaemia
- Contributes to the reduction of tiredness and fatigue — adequate B12 levels support overall vitality
- Contributes to normal homocysteine metabolism — elevated homocysteine is a cardiovascular risk factor
- Contributes to normal psychological function — supports mood and cognitive function
- Contributes to the normal function of the immune system — necessary for immune cell function
How to take Vitamin B12
Vitamin B12 is available in several forms:
- Cyanocobalamin — the most common and well-studied synthetic form, stable and affordable
- Methylcobalamin — an active form that the body can use directly without prior conversion
- Hydroxocobalamin — long-acting form, often used in injections
The recommended daily intake for adults is 2.5 mcg, but supplements often contain higher doses (100–1000 mcg) because absorption is limited. B12 is water-soluble and excess amounts are excreted in urine.
B12 can be taken at any time, but morning consumption with food may improve absorption.
Who should consider B12 supplementation?
- Vegans and vegetarians — plant-based diets do not provide sufficient B12
- Adults over 50 — stomach acid production decreases with age, making B12 absorption from food more difficult
- Pregnant and breastfeeding women — increased demand for foetal and infant development
- People with digestive disorders — coeliac disease, Crohn's disease and other conditions can impair absorption
- Users of certain medications — metformin and proton pump inhibitors can reduce B12 absorption
Frequently asked questions
Can you overdose on B12?
B12 is a water-soluble vitamin and excess amounts are excreted in urine. No toxicity has been observed even at high doses.
How do I know if I have a B12 deficiency?
B12 levels can be measured with a blood test. Common deficiency symptoms include fatigue, numbness in hands and feet, balance problems and memory issues. Consult your doctor.
Is methylcobalamin better than cyanocobalamin?
Both forms have their advantages. Methylcobalamin is the bioactive form, but cyanocobalamin is more stable and better studied. For most people, either form is suitable.
Does B12 give you energy?
B12 contributes to normal energy-yielding metabolism but does not act as a stimulant. If you have a B12 deficiency, supplementation may help reduce fatigue. At normal levels, additional supplementation will not increase energy.
Can I take B12 with other vitamins?
Yes, B12 works well alongside other B vitamins, especially folic acid, as they work together in homocysteine metabolism.
References
1. Green R, Allen LH, Bjørke-Monsen AL, et al. (2017). Vitamin B12 deficiency. Nature Reviews Disease Primers, 3, 17040.
2. Stabler SP. (2013). Vitamin B12 deficiency. New England Journal of Medicine, 368(2), 149-160.
3. Pawlak R, Parrott SJ, Raj S, et al. (2013). How prevalent is vitamin B12 deficiency among vegetarians? Nutrition Reviews, 71(2), 110-117.
4. O'Leary F, Samman S. (2010). Vitamin B12 in health and disease. Nutrients, 2(3), 299-316.
---
See also:
Disclaimer
A food supplement is not a substitute for a varied and balanced diet and a healthy lifestyle.
