Bioavailability of heptaglutamyl relative to monoglutamyl folic acid in healthy adults123

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ABSTRACT

Background

The bioavailability of dietary folate has been estimated to be ≈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.

Key Words

Polyglutamyl folic acid
monoglutamyl folic acid
folic acid
bioavailability
bioefficacy
serum folate
erythrocyte folate
plasma homocysteine

Cited by (0)

1

From the Wageningen Centre for Food Sciences (AM-B, MBK, and PV) and the Division of Human Nutrition (AM-B, CEW, MBK, FJK, and PV), Wageningen University, Wageningen, Netherlands, and the Department of Gastroenterology and Hepatology, University Medical Centre, Nijmegen, Netherlands (CEW).

2

Supported by the Wageningen Centre for Food Sciences, an alliance of major Dutch food industries, Maastricht University; TNO Nutrition and Food Research; Wageningen University and Research Centre; and the Dutch government.

3

Address reprint requests to P Verhoef, Division of Human Nutrition and Epidemiology, Wageningen University, PO Box 8129, 6700 EV Wageningen, Netherlands. E-mail: [email protected].