EFFECT OF FOLIC AND FOLINIC ACIDS ON ZINC INTESTINAL-ABSORPTION

We have investigated the effect of folic and folinic acids on intestinal zinc absorption in humans, using zinc tolerance tests. Zinc (30 mg) as the gluconate was given by mouth to 10 healthy subjects, alone (1), with 200 mg of folic acid (2) or with 200 mg of folinic acid (3). The zinc/folate molar ratio was 1:1. These three oral loading doses were given after overnight fasting to each of the 10 subjects, at weekly intervals. Serum zinc was measured at 0, 1, 2, 3, 6, 12 and 24 h. Zinc was also determined in urine collected for a 6-hour period following the ingestion of oral loading dose. The results do not indicated any inhibition of zinc absorption and urinary zinc excretion by folates. The areas under the curves varied from 48.2 +/- 20.0-mu-mol/6 h (1) to 57.0 +/- 10.3-mu-mol/6 h (3), peak zinc concentration from 28.8 +/- 7.3-mu-mol/l (1) to 32.1 +/- 4.1-mu-mol/l (3), half-life from 3.12 +/- 1.12 h (3) to 3.42 +/- 1.48 h (1), elimination rate constant from 0.22 +/- 0.08 (1) to 0.24 +/- 0.07 (3), mean urinary zinc excretion from 58.1-mu-mol/6 h (2) to 98.7-mu-mol/6 h (1) and mean zinc clearance from 1.15 l/h (3) to 3.26 l/h (1). All these indices were not statistically significantly different among the three different loading doses.