Enterohepatic circulation of vitamin D: a reappraisal of the hypothesis.

Vitamin-D metabolites in bile were investigated after oral and intravenous doses of radioactively labelled vitamin D had been given to six patients with T-tube biliary drainage after cholecystectomy. The vitamin was mainly excreted as highly polar inactivation products and less than 4% of the metabolites in bile were present as 25-hydroxyvitamin D or its glucuronide conjugate. There was insufficient vitamin D or 25-hydroxyvitamin D in bile for the reabsorption of these metabolites to make a significant contribution to normal vitamin-D status. Therefore interference with an enterohepatic circulation of vitamin-D metabolites cannot be a cause of vitamin-D deficiency.