CBL

۱۱۶ طرفدار

۴۲ انتشار • فعال از ۲۰۱۸

Vitamin B12, also known as cobalamin or extrinsic factor, is a water-soluble vitamin involved in metabolism. It is one of B vitamins. It plays an essential role in the nervous system by supporting myelin synthesis. It is needed for DNA synthesis and for the maturation of red blood cells in the bone marrow. It serves also as a vital cofactor in both fatty acid and amino acid metabolism. As humans cannot make it, it is required in the diet, making it an essential nutrient. Animals require B12 but plants do not, relying instead on alternative enzymatic pathways. Vitamin B12 is the most chemically complex of all vitamins, and is synthesized exclusively by certain archaea and bacteria. Natural food sources include meat, shellfish, liver, fish, poultry, eggs, and dairy products. It is also added to many breakfast cereals through food fortification and is available in dietary supplement and pharmaceutical forms. Supplements are commonly taken orally but may be administered via intramuscular injection to treat deficiencies. In healthy adults, vitamin B12 deficiency is not common, mainly because body stores of the vitamin are substantial and turnover is slow, with relatively low dietary requirements. However, B12 deficiency in the elderly is a significant concern, and is related to dementia. The most common cause in developed countries is impaired absorption due to loss of gastric intrinsic factor (IF), required for absorption. A related cause is reduced stomach acid production with age or from long-term use of proton-pump inhibitors, H2 blockers, or other antacids, and interaction with metformin. Elderly people – due to impaired intestinal absorption – and children, premenopausal women, and pregnant women whose diets are low in animal foods are all at increased risk. Deficiency is especially harmful in pregnancy, childhood, and older adults. It can lead to neuropathy, and a type of anemia in which red blood cells become abnormally large.