cyanocobalamin
Meaning of cyanocobalamin: The vitamin the body absorbs with the most difficulty is also the one it stores longest, so deficiency builds quietly over years.
Definition of cyanocobalamin
Cyanocobalamin is a manufactured, stable form of vitamin B12, the cobalt-containing vitamin needed for making red blood cells, building DNA and maintaining the insulating sheath around nerve fibers. It is given as tablets, injections or a nasal spray to treat and prevent B12 deficiency, and it is the form added to fortified foods and to most supplements.
Why is B12 so hard to absorb?
It has the most elaborate absorption route of any vitamin. Stomach acid and enzymes first release it from the protein it is bound to in food. It is then handed to intrinsic factor, a protein made by the same stomach cells that make acid, and the pair travels the whole length of the small intestine to be taken up by specific receptors in its final stretch. Every step is somewhere the process can break. Loss of acid, loss of intrinsic factor, disease or surgical removal of that final stretch of intestine, and bacterial overgrowth consuming the vitamin along the way all cut supply by different routes. Pernicious anemia is the specific case in which the immune system destroys the cells making intrinsic factor. Long-term acid-suppressing medicine, metformin, stomach surgery and a diet with no animal foods each reduce it as well. A small fraction of any dose crosses the intestinal wall without intrinsic factor at all, which is why large doses by mouth can work even when the usual route has failed.
What goes wrong when it runs short?
The liver holds a store measured in years, so supply that stops today produces nothing for a long time, and that delay is why deficiency is rarely traced to its start. When the store empties, two separate problems appear. Red cell production falters and the cells released are abnormally large, a form of anemia visible on a blood count. Separately, the sheath around nerve fibers degrades, beginning in the long tracts at the back of the spinal cord and causing numbness, tingling in the feet and unsteadiness that worsens in the dark. The two do not appear in step. Nerve damage can be well advanced while the blood count still reads normal, and folate taken alone corrects the anemia while leaving the nerve damage to progress unseen.
How do the forms differ?
| Form | Origin | Notes |
|---|---|---|
| Cyanocobalamin | Manufactured | The most stable; carries a cyanide group added during purification, released in trace amounts |
| Hydroxocobalamin | From bacterial culture | Lasts longer after injection; also used at high dose as a cyanide antidote |
| Methylcobalamin and adenosylcobalamin | Made inside cells | The active forms the others are converted into after absorption |
B12 is the one water soluble vitamin the body stockpiles in quantity, which sets it apart from the rest of that group and explains why the timescale of its deficiency is so much longer.
Also known as
Used in a sentence
Cyanocobalamin injections were prescribed after laboratory testing confirmed a vitamin B12 deficiency.
Good to know
Vitamin B12 deficiency can produce nerve-related symptoms before anemia becomes apparent on routine blood testing, which is why levels are sometimes checked in unexplained neurologic symptoms.