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Vitamin B12 is essential for healthy nerve and blood cells. It is also important for making DNA and breaking down homocysteine, an amino acid that can cause problems if it builds up to high levels. Although most people get enough through their diet, various supplementation forms are available for those with difficulty absorbing vitamin B12 into the bloodstream.

What Is Vitamin B12?

Vitamin B12 is the name for a group of closely related vitamins. A deficiency can lead to serious problems such as anemia and permanent, severe nerve damage. While most people get enough vitamin B12 through their diet, some people have difficulty absorbing it into the bloodstream.
Vitamin B12 is available in tablet, sublingual tablet ("under the tongue" tablet), capsule, oral liquid, intramuscular injection, nasal spray, and patch form. Some forms are more reliable than others.
(Click Vitamin B12 Benefits for more information on what the vitamin is used for.)

How Does It Work?

Vitamin B12 is essential for healthy nerve and blood cells. It is also important for making DNA. In addition, the vitamin helps to break down homocysteine, an amino acid that can cause problems if it builds up to high levels. In particular, it is thought that high homocysteine may contribute to problems such as cardiovascular disease or blood clots.
In food, vitamin B12 is bound to protein and is released by stomach acid. Then it binds to a substance known as intrinsic factor (which is produced in the stomach) and is absorbed into the bloodstream through the small intestine. Any problems in either of these steps can result in a deficiency.
To overcome such problems in absorption, vitamin B12 injections (or, more recently, nasal sprays) are often used. Although it was once thought that injections were the only way to treat deficiencies due to low or absent intrinsic factor, it is now known that oral forms can be just as effective, although much higher doses are required. Small amounts of vitamin B12 can be absorbed after oral consumption, even without any intrinsic factor.
Written by/reviewed by:
Last reviewed by: Kristi Monson, PharmD;
Last updated/reviewed:
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