<P> For U.S. food and dietary supplement labeling purposes the amount in a serving is expressed as a percent of Daily Value (% DV). For vitamin B labeling purposes 100% of the Daily Value was 2.0 mg, but as of May 27, 2016 it was revised to 1.7 mg to bring it into agreement with the RDA . A table of the old and new adult Daily Values is provided at Reference Daily Intake . Food and supplement companies have until January 1, 2020 to comply with the change . </P> <P> Vitamin B is absorbed in the jejunum and ileum by passive diffusion . With the capacity for absorption being so great, animals are able to absorb quantities much greater than necessary for physiological demands . The absorption of pyridoxal phosphate and pyridoxamine phosphate involves their dephosphorylation catalyzed by a membrane - bound alkaline phosphatase . Those products and nonphosphorylated forms in the digestive tract are absorbed by diffusion, which is driven by trapping of the vitamin as 5 ′ - phosphates through the action of phosphorylation (by a pyridoxal kinase) in the jejunal mucosa . The trapped pyridoxine and pyridoxamine are oxidized to pyridoxal phosphate in the tissue . </P> <P> The products of vitamin B metabolism are excreted in the urine, the major product of which is 4 - pyridoxic acid . An estimated 40--60% of ingested vitamin B is oxidized to 4 - pyridoxic acid . Several studies have shown that 4 - pyridoxic acid is undetectable in the urine of vitamin B - deficient subjects, making it a useful clinical marker to assess the vitamin B status of an individual . Other products of vitamin B metabolism excreted in the urine when high doses of the vitamin have been given include pyridoxal, pyridoxamine, and pyridoxine and their phosphates . A small amount of vitamin B is also excreted in the feces . </P> <P> The classic clinical syndrome for vitamin B deficiency is a seborrhoeic dermatitis - like eruption, atrophic glossitis with ulceration, angular cheilitis, conjunctivitis, intertrigo, and neurologic symptoms of somnolence, confusion, and neuropathy (due to impaired sphingosine synthesis) and sideroblastic anemia (due to impaired heme synthesis). </P>

Ingested folate requires the addition of what to make it active as a coenzyme