Article

Folate is absorbed across the colon of adults: evidence from cecal infusion of (13)C-labeled [6S]-5-formyltetrahydrofolic acid.

Department of Nutritional Sciences, University of Toronto, Toronto, Canada.
American Journal of Clinical Nutrition (impact factor: 6.67). 06/2009; 90(1):116-23. DOI:10.3945/ajcn.2008.27345
Source: PubMed

ABSTRACT 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.
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.
During screening colonoscopy, 684 nmol (320 microg) [(13)C]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.
The apparent rate of folate absorption across the colon of a bolus dose of [(13)C]5-formyltetrahydrofolic acid infused into the cecum was 0.6 +/- 0.2 nmol/h, as determined by the appearance of [(13)C(5)]5-methyltetrahydrofolic acid in plasma. In comparison, the rate of appearance of [(13)C(5)]5-methyltetrahydrofolic acid after an intravenous injection of [(13)C(5)]5-formyltetrahydrofolate was 7 +/- 1.2 nmol/h.
Physiologic doses of natural folate are absorbed across the intact colon in humans.

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Keywords

6 healthy adults
 
[(13)C]5-formyltetrahydrofolic acid
 
adverse health outcomes
 
apparent rate
 
Blood samples
 
bolus dose
 
comprehensive understanding
 
dietary intakes
 
dietary recommendations
 
direct evidence
 
folate absorption
 
health benefits
 
human diseases
 
input side
 
intact colon
 
Physiologic doses
 
screening colonoscopy
 
synthetic folic acid intake
 
tandem mass spectrometry
 
unlabeled folates