It also regulates cell division and cell growth and is jointly responsible for the formation of DNA and RNA. Too high a homocysteine level is associated with arteriosclerosis. Vitamin B12 enters the small intestine via bile acid. There, the water-soluble vitamin is released into the blood and absorbed by the body in the last part of the small intestine, the ileum.
In order for this process to take place, the transport protein glycoprotein, the so-called intrinsic factor, is required. It binds the vitamin into a complex so that it is protected against digestive enzymes. If the intrinsic factor is disturbed, the vitamin can no longer be absorbed and deficiency symptoms occur.
Vitamin B12 in metabolism
All naturally occurring vitamin B12 is produced by microorganisms located in the intestines of humans and animals, with the human intestine playing a subordinate role. Even if the human body is able to produce vitamin B12 in the large intestine, it cannot be absorbed by the blood there. Absorption is only possible in the last part of the small intestine, and thus the vitamin B12 produced by the body is excreted unused. The human body is very well able to store vitamin B12 ingested through food.
This occurs mainly in the liver, which can store large amounts of vitamin B12 through the protein transcobalamin. If this depot is well filled, a deficiency can be compensated for by the body for months up to several years.
Especially large quantities are contained in animal offal such as liver, kidney and heart. But meat, dairy products, cheese and eggs also contain vitamin B12.
Symptoms of vitamin B12 deficiency
Older people in particular suffer more frequently from a vitamin B12 deficiency because their stomach no longer produces as much of the intrinsic factor with the digestive juice. The first signs of a deficiency are fatigue, depression, lack of concentration, numbness or tingling in the limbs.