You may be low in B12 if you feel constantly cold + tired
Vitamin B12
Vitamin B12 is a member of the vitamin B complex. It contains cobalt, and so is also known as cobalamin. It is exclusively synthesised by bacteria and is found primarily in meat, eggs and dairy products.
Vitamin B12's primary functions are in the formation of red blood cells and the maintenence of a healthy nervous system. B12 is necessary for the rapid synthesis of DNA during cell division. This is especially important in tissues where cells are dividing rapidly, particularly the bone marrow tissues responsible for red blood cell formation. If B12 deficiency occurs, DNA production is disrupted and abnormal cells called megaloblasts occur. This results in anaemia. Symptoms include excessive tiredness, breathlessness, listlessness, pallor, and poor resistance to infection. Other symptoms can include a smooth, sore tongue and menstrual disorders. Anaemia may also be due to folic acid deficiency, folic acid also being necessary for DNA synthesis.
B12 is also important in maintaining the nervous system. . Prolonged B12 deficiency can lead to nerve degeneration and irreversible neurological damage.
When deficiency occurs, it is more commonly linked to a failure to effectively absorb B12 from the intestine rather than a dietary deficiency. Absorption of B12 requires the secretion from the cells lining the stomach of a glycoprotein, known as intrinsic factor. The B12-intrinsic factor complex is then absorbed in the ileum (part of the small intestine) in the presence of calcium. Certain people are unable to produce intrinsic factor and the subsequent pernicious anaemia is treated with injections of B12.
Vitamin B12 can be stored in small amounts by the body. Total body store is 2-5mg in adults. Around 80% of this is stored in the liver.