B12, also called cobalamin, is a vitamin made by bacteria.
Vitamin B12 is an essential vitamin, which is used to make red blood cells and DNA (the source of genetic information for all body cells). B12 is also required for making a protective layer around nerve cells in the nervous system.
A deficiency of B12 leads to there being fewer red blood cells produced than normal, and those which are formed are large immature ones which have reduced ability to carry oxygen. Symptoms include anaemia with severe tiredness; nervous system problems such as numbness, tingling in hands legs, and general degeneration of nerve cells which may lead to paralysis; pale skin and loss of surface texture on the tongue.
There may be insufficient vitamin B12 in the diet, or a problem with absorbing it during the digestive process, or lack of intrinsic factor – a substance which is essential for the absorption of B12 (see below).
Vitamin B12 is manufactured in animals when they consume friendly bacteria from the soil. It has been claimed that some plant foods such as spirulina and tempeh contain vitamin B12. However, these foods only contain an inactive type of B12 that is not useful to the human body, and vegans may be advised to use a vitamin B12 supplement. This is particularly important for children, and those who are pregnant or breastfeeding since a deficiency in B12 can lead to development of brain damage in infants.
Some prepared foods are B12 fortified so check the ingredient listings. If a supplement is taken, it should contain an active form of the vitamin (such as cyanocobalamin or hydroxocobalamin).
The body is capable of storing vitamin B12. The liver is the primary site of storage – sufficient stores of vitamin B12 can usually supply the body’s requirements for between three to five years. Body reserves of vitamin B12 are relatively large in relation to the small amounts required each day. If a person chooses a vegan diet (no dairy products or eggs), it would normally be several years before deficiency symptoms begin to emerge.
It would be worthwhile considering seeing a doctor to have one’s blood tested and B12 levels recorded, and this process repeated at two yearly intervals to check for changes. Symptoms of deficiency often do not appear or are recognised until the state of health has deteriorated considerably.
After being ingested vitamin B12 needs an intrinsic factor to achieve absorption from the small intestine into the blood. Intrinsic factor is a type of protein manufactured in the stomach. It attaches itself to B12 and moves into the small intestine where it enables the B12 to be gradually absorbed.
A lack of intrinsic factor is usually caused by a defect in the gene associated with the factor, or if part of the stomach is removed during surgery. Without intrinsic factor, a person is not able to absorb vitamin B12 – even if they are getting enough B12 from food.
Deficiency of vitamin B12 caused by lack of intrinsic factor is termed ‘pernicious anaemia’. This type of B12 deficiency cannot be treated by diet. Vitamin B12 must be supplied to the body by injections, which bypass the need for intrinsic factor in the small intestine”. (From “Understanding Nutrition”, Whitney, Hamilton & Rolfes, 1990. West Publishing Company, USA.)
Vitamin B12 is quite a stable nutrient. Very little of the vitamin is destroyed during cooking. Even when milk undergoes pasteurisation or UHT treatment, only a small amount is lost. However significantly more B12 is lost in evaporated milk.
Vitamin B12 works closely with another vitamin called folic acid or folate. Vitamin B12 is actually needed to free folate from an inactive state, which allows it to make healthy red blood cells and DNA.