1000 mcg b12 free#

Table 1 lists the current RDAs for vitamin B12. Tolerable Upper Intake Level (UL): Maximum daily intake unlikely to cause adverse health effects.Estimated Average Requirement (EAR): Average daily level of intake estimated to meet the requirements of 50% of healthy individuals usually used to assess the nutrient intakes of groups of people and to plan nutritionally adequate diets for them can also be used to assess the nutrient intakes of individuals.Adequate Intake (AI): Intake at this level is assumed to ensure nutritional adequacy established when evidence is insufficient to develop an RDA.Recommended Dietary Allowance (RDA): Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals often used to plan nutritionally adequate diets for individuals.These values, which vary by age and sex, include: DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. Intake recommendations for vitamin B12 and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the National Academies of Sciences, Engineering, and Medicine. Experts suggest that if a patient’s serum vitamin B12 level is less than 150 pg/ml (111 pmol/L), the patient’s serum MMA levels should be checked to confirm a diagnosis of vitamin B12 deficiency. However, this indicator has poor specificity because it is influenced by other factors, such as low folate levels and, especially, by declines in kidney function. Another marker is total plasma homocysteine levels, which rise quickly as vitamin B12 status declines a serum homocysteine level higher than 15 micromol/L, for example, suggests vitamin B12 deficiency. However, MMA levels also rise with renal insufficiency and tend to be higher in older adults. Levels of serum methylmalonic acid (MMA), a vitamin B12-associated metabolite, are the most sensitive markers of vitamin B12 status, and an MMA level greater than 0.271 micromol/L suggests vitamin B12 deficiency. The cutoff between normal vitamin B12 levels and deficiency varies by method and laboratory, but most laboratories define subnormal serum or plasma values as those lower than 200 or 250 pg/mL (148 or 185 pmol/L). Vitamin B12 status is typically assessed by measurements of serum or plasma vitamin B12 levels.

1000 mcg b12 free#

If vitamin B12 is added to fortified foods and dietary supplements, it is already in free form and therefore does not require the separation step. The resulting complex is absorbed in the distal ileum by receptor-mediated endocytosis. In the duodenum, digestive enzymes free the vitamin B12 from haptocorrin, and this freed vitamin B12 combines with intrinsic factor, a transport and delivery binding protein secreted by the stomach’s parietal cells. More vitamin B12 is released from its food matrix by the activity of hydrochloric acid and gastric protease in the stomach, where it then binds to haptocorrin. The freed vitamin B12 then binds with haptocorrin, a cobalamin-binding protein in the saliva. The process starts in the mouth when food is mixed with saliva. Vitamin B12 is bound to protein in food and must be released before it is absorbed. L-methylmalonyl-CoA mutase converts L-methylmalonyl-CoA to succinyl-CoA in the metabolism of propionate, a short-chain fatty acid. Methionine is required for the formation of S-adenosylmethionine, a universal methyl donor for almost 100 different substrates, including DNA, RNA, proteins, and lipids. Methionine synthase catalyzes the conversion of homocysteine to the essential amino acid methionine. Vitamin B12 functions as a cofactor for two enzymes, methionine synthase and L-methylmalonyl-CoA mutase. Vitamin B12 is required for the development, myelination, and function of the central nervous system healthy red blood cell formation and DNA synthesis. However, two others forms, hydroxycobalamin and cyanocobalamin, become biologically active after they are converted to methylcobalamin or 5-deoxyadenosylcobalamin. Methylcobalamin and 5-deoxyadenosylcobalamin are the metabolically active forms of vitamin B12. Because vitamin B12 contains the mineral cobalt, compounds with vitamin B12 activity are collectively called “cobalamins”. Vitamin B12 is a water-soluble vitamin that is naturally present in some foods, added to others, and available as a dietary supplement and a prescription medication. For a reader-friendly overview of Vitamin B12, see our consumer fact sheet on Vitamin B12. This is a fact sheet intended for health professionals. Health Risks from Excessive Vitamin B12.Groups at Risk of Vitamin B12 Inadequacy.