Colonic mucosal concentrations of folate correlate well with blood measurements of folate status in persons with colorectal polyps

Background: Estimates of habitual dietary folate intake are known to be imprecisely correlated with systemic measures of folate status. Furthermore, measurements of blood folate concentrations may not accurately reflect the concentration of folate in tissues of interest. This issue is important for assessing folate status in the colorectal mucosa because low dietary intake or blood concentrations of folate are associated with an increased risk of colorectal neoplasia. Objective: We examined whether conventional measures of folate in blood and a more sensitive, inverse indicator of systemic folate status, serum homocysteine, accurately reflected folate concentrations in human colonic mucosa obtained by endoscopic biopsy. Design: In 30 persons with colorectal polyps, blood samples were taken and biopsies of normal rectosigmoid mucosa performed at the time of colonoscopic polypectomy. Serum, red blood cell, and colonic mucosal folate and serum homocysteine concentrations were measured. Results: Serum and red blood cell folate and serum homocysteine concentrations accurately reflected colonic mucosal folate concentrations; among these, serum homocysteine correlated best with mucosal concentrations. Folate concentrations in the normal rectosigmoid mucosa were significantly lower in persons with adenomatous polyps than in those with hyperplastic polyps (P = 0.04). Conventional measures of systemic folate status were not significantly lower in those with adenomas, although serum homocysteine was mildly elevated (P = 0.04). Conclusions: Our data underscore the ability of systemic measures of folate status, particularly serum homocysteine, to reflect folate concentrations in the colonic mucosa. Nevertheless, future studies that examine the ability of folate to modulate colorectal carcinogenesis may benefit from direct measurement of folate in the colon.