Biotin intestinal bacterial synthesis

As a result of this resorption and the protein binding of plasma biotin, which reduces filtration at the glomerulus, renal clearance of biotin is only 40% of that of creatinine. This efficient conservation of biotin, together with the recycling of biocytin released from the catabolism of biotin-containing enzymes, may be as important as intestinal bacterial synthesis of the vitamin in explaining the rarity of deficiency. 

On the basis of studies in patients who developed deficiency during total parenteral nutrition, and who are therefore presumably wholly reliant on an exogenous source of the vitamin - with no significant contribution from intestinal bacterial synthesis - the provision of 60 fxg of biotin per day for adults receiving total parenteral nutrition is generally recommended (Bitsch et al., 1985). 

Biotin is widely distributed in many foods. It is synthesized by intestinal flora, and in balance studies the total output of biotin in urine plus faeces is three- to sixfold greater than the intake, reflecting bacterial synthesis. It is not known to what extent this is available to the host (see also Problem 10.4). 

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