is added to commercial dried cereals. The RDA is 2.4 mcg a day. Deficiencies are rare in young people, although the elderly may have trouble absorbing natural vitamin B12 and require synthetic forms from supplements and fortified foods. Symptoms of mild B12 deficiency include memory loss, instability, disorientation, and decreased reflexes, and possibly and hearing loss. Deficiencies also elevate homocysteine (see vitamin B6, above). When vitamin B12 deficiencies are caused by a genetic defect, in which a protein known as gastric intrinsic factor is lacking, a serious disorder known as pernicious anemia can develop, which must be treated with injections of vitamin B12 or else neurologic damage may occur.Deficiencies and Toxicity of BiotinBiotin, also a B vitamin, is involved in the production of amino acid proteins and fatty acids. It is obtained not only in diet but is also produced by bacteria in the intestines. Dietary sources are eggs, milk, liver, mushrooms, bananas, tomatoes, whole grains, nuts, and brewer's yeast. There is no DRI for biotin; some experts suggest 30-100 mcg. Deficiencies are almost unheard of. There is no evidence of toxicity with this vitamin.Deficiencies and Toxicity of FolateFolate is a B vitamin compound that is important for many metabolic processes in the body and is used in the manufacture of neurotransmitters (chemical messengers in the brain), in preventing heart disease, and for synthesizing DNA. Folate is best found in avocado, bananas, orange juice, cold cereal, asparagus, fruits, green, leafy vegetables, dried beans and peas, and yeast. The synthetic form, folic acid, is now added to commercial grain products. Vitamins are usually made from folic acid, which is about twice as potent as folate. Many experts now recommend that adults have 400 mcg of folic acid daily, which is considerably higher than the DRI recommendations of 400 mcg of folate, which does not take into consideration the possible benef...
