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This Article Full Text Full Text (PDF) Supplemental data All Versions of this Article: 90/1/116    most recent ajcn.2008.27345v1 Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Citation Map Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Aufreiter, S. Articles by O'Connor, D. L PubMed PubMed Citation Articles by Aufreiter, S. Articles by O'Connor, D. L Agricola Articles by Aufreiter, S. Articles by O'Connor, D. L

Folate is absorbed across the colon of adults: evidence from cecal infusion of ¹³C-labeled [6S]-5-formyltetrahydrofolic acid^1,2,3

¹ From the Departments of Nutritional Sciences (SA, Y-IK, DLO, and PBP), Medicine (Y-IK and NM), and Paediatrics (PBP), University of Toronto, Toronto, Canada; The Research Institute, The Hospital for Sick Children, Toronto, Canada (SA, DLO, and PBP); the Division of Gastroenterology, St Michael's Hospital, Toronto, Canada (Y-IK, NM, and PK); the Food Science and Human Nutrition Department, University of Florida, Gainesville, FL (JFG); and the Centers for Disease Control and Prevention, Atlanta, GA (CMP and ZF).

² Supported by the National Sciences & Engineering Research Council of Canada. SA was funded by the Ontario Student Opportunity Trust Fund, The Hospital for Sick Children Foundation Scholarship Program, and the Ontario Ministry of Training–Colleges and Universities (OGS scholarship).

³ Address correspondence to DL O'Connor, Department of Nutritional Sciences, University of Toronto, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada, M5G 1X8. E-mail: deborah_l.o'connor{at}sickkids.ca.

Background: Folate deficiency increases the risk of several human diseases. Likewise, high intakes of folate, particularly synthetic folic acid intake, may be associated with adverse health outcomes in humans. A more comprehensive understanding of the "input side" of folate nutrition may help to set dietary recommendations that strike the right balance between health benefits and risks. It is well known that the microflora in the colon produce large quantities of folate that approach or exceed recommended dietary intakes; however, there is no direct evidence of the bioavailability of this pool in humans.

Objective: The objective was to determine whether, and to what extent, the natural folate vitamer 5-formyltetrahydrofolic acid is absorbed across the intact colon of humans.

Design: During screening colonoscopy, 684 nmol (320 µg) [¹³C]glutamyl-5-formyltetrahydrofolic acid was infused directly into the cecum of 6 healthy adults. Three or more weeks later, each subject received an intravenous injection of the same compound (172 nmol). Blood samples were collected before and after each treatment. The ratio of labeled to unlabeled folates was determined in plasma by tandem mass spectrometry.

Results: The apparent rate of folate absorption across the colon of a bolus dose of [¹³C]5-formyltetrahydrofolic acid infused into the cecum was 0.6 ± 0.2 nmol/h, as determined by the appearance of [¹³C₅]5-methyltetrahydrofolic acid in plasma. In comparison, the rate of appearance of [¹³C₅]5-methyltetrahydrofolic acid after an intravenous injection of [¹³C₅]5-formyltetrahydrofolate was 7 ± 1.2 nmol/h.

Conclusion: Physiologic doses of natural folate are absorbed across the intact colon in humans.