Bioavailability of heptaglutamyl relative to monoglutamyl folic acid in healthy adults.
BACKGROUND
The bioavailability of dietary folate has been estimated to be approximately 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.


METHODS
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%).


CONCLUSIONS
The polyglutamate chain of folates in the diet reduces their bioavailability.
Wageningen Centre for Food Sciences, Wageningen University, Wageningen, Netherlands.
Alida
A
Melse-Boonstra
Clive E
CE
West
Martijn B
MB
Katan
Frans J
FJ
Kok
Petra
P
Verhoef
D000284:Administration, Oral; D000368:Aged; D001682:Biological Availability; D019587:Dietary Supplements; D004311:Double-Blind Method; D004912:Erythrocytes / Q000737:chemistry; D005260:Female; D005492:Folic Acid / Q000031:analogs & derivatives* / Q000097:blood / Q000493:pharmacokinetics*; D006710:Homocysteine / Q000097:blood*; D006801:Humans; D007408:Intestinal Absorption / Q000187:drug effects; D008297:Male; D008875:Middle Aged; D011624:Pteroylpolyglutamic Acids / Q000493:pharmacokinetics
D011624:Pteroylpolyglutamic Acids; D006710:Homocysteine; D005492:Folic Acid