Folate Absorption across the Colon: Caplet Study

The purpose of this study was to determine the absorption of [13C]5-formyltetrahydrofolic acid across the human colon with an intact microflora. Bioavailability was determined after administration of a pH-dependent acrylic co-polymer coated barium sulphate caplet containing 855 nmol and measuring the plasma appearance of [13C5]5-methyltetrahydrofolic acid compared to an intravenous injection of the same compound (214 nmol). Blood samples serially collected after both test doses were analyzed by microbiological assay and tandem mass spectrometry to determine total folates and ratio of labeled to unlabeled folates, respectively. Caplet disintegration in the colon was quantitatively assessed by fluoroscopic imaging for six of nine subjects. The plasma [13C5]5-methyltetrahydrofolic acid appearance rate was 4 + 0.9 nmol/h (intravenous) and 0.35 + 0.02 nmol/h (caplet). Mean apparent absorption across the colon was 35%. These findings suggest that physiological doses of natural folate are absorbed across the human colon in the presence of an undisturbed microbiota.MAS