Colonic mucosal concentrations of folate are accurately predicted by bloodmeasurements of folate status among individuals ingesting physiologic quantities of folate

Folate status is inversely related to the risk of colorectal cancer. Whethe r conventional blood measurements of folate status accurately reflect folat e concentrations in the colorectal mucosa has been a controversial topic. T his is an important issue because accurate measures of folate status in the colorectal mucosa are important for ascertaining the risk of colorectal ca ncer in epidemiological studies and for determining the effects of folate s upplementation in clinical trials. We examined whether conventional blood m easurements of folate and a more sensitive, inverse indicator of systemic f olate status, serum homocysteine, accurately reflect folate concentrations in human colonic mucosa obtained by endoscopic biopsy. Study subjects (n = 20) were participants in a randomized trial that investigated the effect of folate supplementation (5 mg daily for 1 year) on provisional molecular ma rkers of colon cancer. Blood samples and biopsies of normal rectosigmoid mu cosa were obtained at baseline, at 6 months, and at 1 year. Serum, RBC, and colonic mucosal folate and serum homocysteine concentrations were determin ed. Colonic mucosal folate concentrations correlated directly with serum fo late concentrators at each time point (r = 0.572 0.845; P < 0.015) and with RBC folate concentrations at 6 months and 1 year (r = 0.747-0.771; P < 0.0 01). Colonic mucosal folate concentrations correlated inversely with serum homocysteine concentrations at each time point (r = -0.622-0.666; P < 0.008 ). Systemic measures of folate status did not correlate with colonic mucosa l folate concentrations among individuals receiving supplemental folate, Ou r observations indicate that colonic mucosal concentrations of folate may b e predicted accurately by blood measurements of folate status only among in dividuals not ingesting supraphysiological quantities of folate.