Bioavailability of heptaglutamyl relative to monoglutamyl folic acid in healthy adults

• Published in: The American journal of clinical nutrition Vol. 79; no. 3; pp. 424 - 429
• Main Authors: Melse-Boonstra, A, West, C.E, Katan, M.B, Kok, F.J, Verhoef, P
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Clinical Nutrition 01-03-2004; American Society for Clinical Nutrition, Inc
• Subjects: absorption; Administration, Oral; Adults; Aged; availability; beans; Bioavailability; Biological and medical sciences; Biological Availability; deuterium-labeled monoglutamyl; Dietary Supplements; Double-Blind Method; Erythrocytes - chemistry; Feeding. Feeding behavior; Female; Folic Acid - analogs & derivatives; Folic Acid - blood; Folic Acid - pharmacokinetics; foods; Fundamental and applied biological sciences. Psychology; Health; Homocysteine - blood; Humans; Intestinal Absorption - drug effects; Male; Middle Aged; plasma homocysteine concentrations; polyglutamate folate; Pteroylpolyglutamic Acids - pharmacokinetics; risk; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Vitamin B; women; Human; monoglutamyl folic acid; erythrocyte folate; Red blood cell; Bioavailability; Polyglutamyl folic acid; Folic acid; Folate; bioefficacy; Blood plasma; serum folate; Blood cell; Homocystein; plasma homocysteine; Adult; Serum
• ISSN: 0002-9165; 1938-3207
• DOI: 10.1093/ajcn/79.3.424

Background: The bioavailability of dietary folate has been estimated to be approximately equal to 50% of that of synthetic folic acid. Folate in the diet is linked to a polyglutamate chain that may restrict folate absorption. Objective: Our goal was to quantify the bioavailability and bioefficacy of low doses of polyglutamyl folic acid relative to that of monoglutamyl folic acid. Design: In total, 180 men and women aged 50-75 y ingested capsules containing 323 nmol heptaglutamyl folic acid/d or 262 nmol monoglutamyl folic acid/d or placebo in a randomized parallel trial. Serum and erythrocyte folate and plasma homocysteine concentrations were measured after an overnight fast at baseline and after 12 wk of intervention. Results: Mean serum and erythrocyte folate concentrations increased less in the polyglutamyl folic acid group [6.1 (95% CI: 5.3, 7.0) and 155 (122, 188) nmol/L, respectively] than in the monoglutamyl folic acid group [11.8 (10.3, 13.3) and 282 (246, 318) nmol/L, respectively]. Differences remained statistically significant (P < 0.05) after correction for the difference in the amount of folic acid administered. The decrease in plasma homocysteine concentrations did not differ significantly between treatment groups [polyglutamyl: -12.1% (-14.8%, -9.3%); monoglutamyl: -14.1% (-16.3%, -11.9%)]. The relative bioavailability of polyglutamyl folic acid was 64% (52%, 75%) on the basis of serum folate and was 68% (51%, 84%) on the basis of erythrocyte folate concentrations. Bioefficacy, determined by changes in plasma homocysteine concentrations, was 106% (77%, 134%). Conclusion: The polyglutamate chain of folates in the diet reduces their bioavailability.