Folate synthesized by bacteria in the human upper small intestine is assimilated by the host

Gastroenterology. 1996 Apr;110(4):991-8. doi: 10.1053/gast.1996.v110.pm8613033.


Background & aims: Some intestinal flora are known to synthesize folate. The aim of this study was to determine whether folate synthesized by small intestinal flora is assimilated by the human host.

Methods: Subjects with atrophic gastritis and healthy volunteers were studied before and after omeprazole administration. A double-lumen perfusion tube was placed in the duodenum. 3H-labeled P-aminobenzoic acid, a precursor substrate for bacterial folate synthesis, was perfused. Downstream intestinal aspirates and a 48-hour urine collection were obtained.

Results: Atrophic gastritis and omeprazole administration were associated with increases in duodenal pH and in small intestinal flora. Bacterially synthesized folates were isolated from the intestinal aspirates. Tritiated 5-methyltetrahydrofolate, a major metabolite of folate, was isolated from the urine of omeprazole-treated subjects in greater quantities than from drug-free subjects (P<0.01); the quantity of tritiated 5-methyltetrahydrofolate in the urine of the subjects with atrophic gastritis was similarly elevated.

Conclusions: (1) Mild bacterial overgrowth caused by atrophic gastritis and administration of omeprazole are associated with de novo folate synthesis in the lumen of the small intestine; (2) the human host absorbs and uses some of these folates; and (3) the contribution to folate nutriture from this source remains unclear.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 4-Aminobenzoic Acid / metabolism
  • Adult
  • Aged
  • Analysis of Variance
  • Anti-Ulcer Agents / therapeutic use
  • Bacteria / growth & development
  • Bacteria / isolation & purification
  • Bacteria / metabolism*
  • Female
  • Folic Acid / biosynthesis
  • Folic Acid / metabolism*
  • Gastritis, Atrophic / drug therapy
  • Gastritis, Atrophic / metabolism
  • Gastritis, Atrophic / microbiology
  • Humans
  • Hydrogen-Ion Concentration
  • Intestinal Absorption
  • Intestine, Small / metabolism
  • Intestine, Small / microbiology*
  • Male
  • Omeprazole / therapeutic use
  • Tetrahydrofolates / urine


  • Anti-Ulcer Agents
  • Tetrahydrofolates
  • Folic Acid
  • Omeprazole
  • 4-Aminobenzoic Acid
  • 5-methyltetrahydrofolate