Cobalt is a chemical element and belongs to the so-called iron-platinum group. It is often found together with nickel and iron. Biologically, it plays a major role as the central atom of vitamin B12.
What is cobalt?
Cobalt is an iron-like metal with atomic number 27. The name cobalt comes from Latin and means cobold. Cobalt was once held as a valuable silver or copper ore. However, because it could not be processed and gave off foul-smelling fumes when heated due to its arsenic content, miners referred to it as cobold. The metal rarely occurs in the earth’s crust compared to other elements. In nature it is always associated with nickel. Cobalt is a trace element that occurs in most soils. There are some cobalt ores, which were formed by weathering processes. However, its yield in the sulfide ores is very low, only 0.1 to 0.3 percent. Elemental cobalt shows up as a tough heavy metal that occurs in two modifications. Like all metals, cobalt conducts electricity and heat very well. In air, it is passivated by a surface oxidation layer. Cobalt can form complex compounds with organic molecules. A typical example is cobalamin (vitamin B12).
Function, action, and roles
Cobalt is extremely important for the human organism in the form of complex compounds, also known as cobalamins. The cobalamins represent the vitamin B12 group. Here, a cobalt atom acts as the central atom of a complex with six ligands. The cobalt atom is surrounded by the four nitrogen atoms of a corrin ring. A fifth nitrogen ligand is derived from a 5,6-dimethyl-benzimidazole ring, which is nucleotide-bonded to the corrin ring. The sixth ligand is interchangeable and is responsible for differentiating the various cobalamins. The only active form of vitamin B12 is the complex adenosylcobalamin. Adenosylcobalamin is also the coenzyme B12. The cobalamins are so far the only known organometallic compounds in which cobalt plays an important role in biological processes. Vitamin B12 acts as a coenzyme for two enzymatic processes. It is involved in the conversion of homocysteine to methionine. In this process, homocysteine is methylated. This reaction is a central component of all methylation reactions. The other enzymatic reaction helps break down odd-numbered fatty acids and some amino acids to succinyl-CoA. This compound is an intermediate of the citric acid cycle. Cobalamins cannot be produced in the human organism. Therefore, humans are dependent on dietary intake. It is true that vitamin B12 is produced by intestinal bacteria in the large intestine. However, it can only be absorbed in the small intestine, so that the cobalamin synthesized in the large intestine is of no physiological significance. Vitamin B12 is stored in the liver. From there, it enters the small intestine via bile acids and is absorbed there in the ileum by intrinsic factor. Thus, with reduced intake, the body’s own requirement can be met for years.
Formation, occurrence, properties, and optimal values
Cobalt is found in its biologically active form in vitamin B12 in all foods that are of animal origin. Purely plant-based foods do not contain sufficient cobalamin. Biosynthesis of the vitamin occurs by bacteria. Herbivores meet their needs through special intestinal flora. Humans cannot utilize the cobalamin produced in the large intestine because it is formed below the ileum. Here it is excreted unused. However, herbivores also depend on pastures with a sufficiently high concentration of cobalt. Therefore, cobalt compounds must be mixed into the animals’ feed when soils are low in cobalt. A cobalt deficiency manifests itself in the animals as increasing anemia because vitamin B12 can no longer be formed in sufficient quantities.
Diseases and disorders
Anemia can also develop in humans due to a deficiency of vitamin B12. However, this deficiency cannot be corrected by supplementation with cobalt. As mentioned earlier, vitamin B12 produced by bacteria in the human large intestine is not utilized. Humans depend on the supply of cobalamin in the diet. Since mainly animal foods can be considered as a source of cobalamin, vegetarians are additionally dependent on vitamin B12 supplements.However, cobalamin has a half-life of 450 to 750 days in the body. It is stored in the liver and can be taken up again and again via the intrinsic factor. Therefore, the stored reserves in the liver last for several years, even if the intake is limited. Humans have a daily requirement of 3 micrograms. When there is an actual deficiency of vitamin B12, anemia develops. In addition, psychological problems develop, due to a disturbance of the hindbrain and pyramidal pathways. Furthermore, the blood concentration of homocysteine increases because its methylation to methionine comes to a halt. Elevated homocysteine levels promote the development of atherosclerosis. At the same time, the methyl group donor N5-methyl-tetrahydrofolate (N5-methyl-THF) can no longer be converted back into THF (tetrahydrofolate). Among other things, THF is responsible for the formation of nucleic bases, so that nucleic acid formation is also inhibited. As a result, hematopoiesis is delayed and the few red blood cells are still overloaded with hemoglobin. Anemia has developed, which can be corrected by administration of folic acid or, even better, vitamin B12. When the absorption of vitamin B12 is impaired by the absence of intrinsic factor, pernicious anemia results.
