Vitamin B12 deficiency

Vitamin B12 deficiency refers to low levels of Vitamin B12 in the body.

This can lead to a variety of problems ranging from anemia to soreness of the tongue and neurological dysfunction.

Vitamin B12, also known as cobalamin, is a complex organometallic compound found in animal and dairy products like meat, eggs or milk.

Dairy and animal products are broken down in the stomach by pepsin, which is the active form of a gastric enzyme called pepsinogen, to release B12.

Then, a protein made by parietal cells in the stomach, called intrinsic factor, can bind to B12, and the B12-intrinsic factor complex passes into the intestines.

When the complex reaches the terminal ileum, the enterocytes, which are the special cells lining the intestines, recognize intrinsic factor and absorb the whole complex.

Inside the enterocytes, intrinsic factor gets removed and a special protein called transcobalamin-II binds the free B12 and transports it into the blood and from there, to various target tissues.

Some of the transcobalamin-B12 complex gets to the liver, where B12 can be stored for several years.

B12 is used to synthesize DNA precursors, which is essential for cell division.

First, vitamin B12 accepts a methyl group from methyl tetrahydrofolate or methyl-THF, making methylcobalamin and free tetrahydrofolate, or THF in the process.

THF then gets an extra “methylene” group from serine, an amino acid found within the cells.

THF quickly transfers the methylene to a nucleotide called deoxyuridine monophosphate, or d-UMP for short.

As a result, d-UMP becomes d-TMP or deoxythymidine monophosphate, which can then be converted to thymidine, one of the nucleotides used to build DNA.

Going back, the methylcobalamin that was formed along with THF transfers its methyl group to homocysteine and converts it into an essential amino acid called methionine, thus lowering the levels of homocysteine in the body, too much of which can be harmful.

Alternatively, B12 can be used by the mitochondria in another active form called “adenosylcobalamin” - which is basically B12 with an adenosyl group clinging to it! Adenosylcobalamin acts as a coenzyme for methylmalonyl coenzyme A mutase, an enzyme which converts methylmalonyl co-A into succinyl co-A.