cobalamin
Meaning of cobalamin: The only vitamin that contains a metal, and the only one the liver can stockpile for years at a time.
Definition of cobalamin
Cobalamin is vitamin B12, a large water-soluble vitamin built around a single cobalt atom. The body cannot make it and obtains it almost entirely from animal foods such as meat, fish, eggs and milk. It is needed for two specific chemical reactions, one that keeps nerve insulation intact and one that allows red blood cells and DNA to be built normally.
Why is absorption so complicated?
Most vitamins are absorbed simply. This one needs a chain of steps, and a break anywhere along it causes a shortage even when the diet is generous. Stomach acid and enzymes first release the vitamin from the food protein it arrives bound to. The stomach lining then supplies a carrier called intrinsic factor, which escorts it the length of the small intestine to a specific docking site in the last section, the ileum. Loss of the acid-producing cells, removal of part of the stomach, disease or surgery involving the ileum, and long term suppression of stomach acid can each interrupt the chain.
What does a shortage do?
Two very different problems appear, and they do not always appear together. The blood problem is a form of anemia in which red cells are made too large and too few, because dividing cells cannot build DNA properly. The nerve problem is a slow degeneration of the spinal cord and the peripheral nerves, producing numbness, unsteadiness and, in some cases, changes in memory and mood. Nerve damage can develop while the blood count still looks normal, so a normal count does not rule the shortage out.
How does it differ from the other B vitamins?
| Feature | Cobalamin | Most other B vitamins |
|---|---|---|
| Dietary source | Animal foods and fortified products only | Plants and animals |
| Storage | Enough for several years held in the liver | Little or none |
| Absorption | Needs intrinsic factor from the stomach | Taken up directly |
The storage difference matters most. It is classed as a water-soluble vitamin, which normally implies little reserve, and it is the exception to that rule. Plants contain essentially none, which is why it is the nutrient most often added to foods and supplements aimed at people who avoid animal products.
What is its relationship with folate?
The two work in the same reaction, and cobalamin is needed to release folate into the form the body can use. Folate given alone can correct the anemia of cobalamin shortage while leaving the nerve damage to progress unchecked and unnoticed. That interaction is the reason the two are usually measured and considered together.
Also known as
Used in a sentence
Cobalamin was measured alongside folate to investigate the enlarged red cells.
Good to know
Nerve damage from cobalamin shortage can begin before the blood count becomes abnormal, and folate given on its own corrects the anemia while the neurological damage continues.