The known roles of Vitamin B12 in the body are connected with some chemical groups known as ‘active methyl groups’. These are of importance in the synthesis of nucleic acids the replenishment of the amino acid methionine, and production of two important substances called choline and creatine. There are also some other connections with amino acid metabolism. The intake of Vitamin B12 normally needed is only about 4mcg (micrograms not milligrams this time), which is an extremely small amount, far less than any other Vitamins we have discussed. The UK RNIs are still less. Supplemental intake levels average 25mcg and range from 10 to 50mcg per day. Apart from pernicious anaemia, there are a good many other symptoms and illnesses reported as being helped by giving Vitamin B12, but most probably the effects are generally non specific, reflecting the general improvement in body biochemistry when the Vitamin is present. It should be noted that most cases of pernicious anaemia arise not on account of Vitamin B12 deficiency in the diet, but because the stomach fails to produce a specific substance, called \Intrinsic Factor\ which is needed for Vitamin B12 absorption. >>Source
Uses in the body: contributes towards healthy nervous and cardiovascular systems, the formation of red blood cells and bone marrow, production of genetic material and metabolism of fats, proteins and carbohydrates.
Signs of deficiency: exhaustion, anaemia, pallor, pins and needles in hands and feet, irritability, depression, shortness of breath on exertion.
Therapeutic uses: anaemia, fatigue, digestive problems, mental or nervous problems. Vegans and vegetarians can become deficient in B12 as it’s mainly found in animal produce.
Dietary sources: meat (especially liver), fish, eggs, dairy produce, fortified cereals, brewer’s yeast, yeast extract, blackstrap molasses, seaweed (it’s present in blue-green algae such as spirulina and chlorella, but it may not be well absorbed by the body).
Recommended daily allowance: 1µg
Typical therapeutic daily dose: 100µg to 1,000µg
Daily intake shouldn’t exceed: 3,000µg
Cautions: the form hydroxycobalamin is preferable to cyanocobalamin, which can aggravate certain eye conditions. Check the labels. Toxicity is very rare.
Best taken: by injection for best absorption. Drops (taken with water or under the tongue) may be better absorbed than tablets. Take at breakfast with food.