Absorption of the phosphate forms involves their dephosphorylation catalyzed by the enzyme alkaline phosphatase. Most of the vitamin is taken up by the liver. There, the dephosphorylated vitamins are converted to the phosphorylated PLP, PNP and PMP, with the two latter converted to PLP. In the liver, PLP is bound to proteins, primarily albumin. The PLP-albumin complex is what is released by the liver to circulate in plasma. Protein-binding capacity is the limiting factor for vitamin storage. Total body stores, the majority in muscle, with a lesser amount in liver, have been estimated to be in the range of 61 to 167 mg.Enzymatic processes utilize PLP as a phosphate-donating cofactor. PLP is restored via a salvage pathway that requires three key enzymes, pyridoxal kinase, pyridoxine 5-phosphate oxidase, and phosphatases. Inborn errors in the salvage enzymes are known to cause inadequate levels of PLP in the cell, particularly in neuronal cells. The resulting PLP deficiency is known to cause or implicated in several pathologies, most notably infant epileptic seizures.The end-product of vitamin B6 catabolism is 4-pyridoxic acid, which makes up about half of the B6 compounds in urine. 4-Pyridoxic acid is formed by the action of aldehyde oxidase in the liver. Amounts excreted increase within 1–2 weeks with vitamin supplementation and decrease as rapidly after supplementation ceases. Other vitamin forms excreted in the urine include pyridoxal, pyridoxamine and pyridoxine, and their phosphates. When large doses of pyridoxine are given orally, the proportion of these other forms increases.
In 2001, MHLW enacted a new regulatory system, Foods with Health Claims (保健機能食品; FHC), which consists of the existing FOSHU system and the newly established Foods with Nutrient Function Claims (栄養機能表示食品; FNFC), under which claims were approved for any product containing a specified amount per serving of 12 vitamins, including vitamin B6, and two minerals. To make a health claim based on a foods vitamin B6 content, the amount per serving must be in the range of 0.3–25 mg. The allowed claim is: "Vitamin B6 is a nutrient that helps produce energy from protein and helps maintain healthy skin and mucous membranes. "In 2010, the European Food Safety Authority (EFSA) published a review of proposed health claims for vitamin B6, disallowing claims for bone, teeth, hair skin and nails, and allowing claims that the vitamin provided for normal homocysteine metabolism, normal energy-yielding metabolism, normal psychological function, reduced tiredness and fatigue, and provided for normal cysteine synthesis.The US Food and Drug Administration (FDA) has several processes for permitting health claims on food and dietary supplement labels. There are no FDA-approved Health Claims or Qualified Health Claims for vitamin B6. Structure/Function Claims can be made without FDA review or approval as long as there is some credible supporting science. Examples for this vitamin are "Helps support nervous system function" and "Supports healthy homocysteine metabolism." Absorption, metabolism and excretion
Vitamin B6 is absorbed in the jejunum of the small intestine by passive diffusion. Even extremely large amounts are well absorbed.