Effect of Iron, Vitamin B-6 and Picolinic Acid on Zinc Absorption in the Rat

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Abstract
True daily zinc absorption was determined in rats fed a high iron diet (220 ppm Fe; 16.5 ppm Zn), an adequate iron diet (30 ppm Fe) and a high iron diet with varying levels of pyridoxine-HCl (2–40 ppm). Zinc absorption in rats fed the high iron diet was significantly less than in rats fed the adequate iron diet. Zinc absorption in rats fed the high iron diet supplemented with picolinic acid (200 ppm) was markedly increased and did not differ from that in rats fed the adequate iron diet. True, daily zinc absorption increased as the level of dietary vitamin B-6 was increased. Zinc absorption was the least in rats fed 2 ppm vitamin B-6 and was greatest in rats fed 40 ppm vitamin B-6. The concentration of picolinic acid in the pancreas increased as the level of dietary vitamin B-6 was increased. Zinc absorption was significantly elevated in rats fed the high iron diet that contained either 4 or 10 ppm vitamin B-6 and 200 ppm picolinic acid. The turnover rate of 65Zn was determined in rats fed an adequate iron, marginal zinc diet (8.5 ppm Zn) with varying levels of vitamin B-6. The turnover of 65Zn was greatest in rats fed 2 ppm vitamin B-6 and least in rats fed 40 ppm vitamin B-6 or 2 ppm vitamin B-6 + 200 ppm picolinic acid. The results suggest that high levels of dietary iron inhibit zinc absorption via competition for binding with endogenous picolinic acid. The results provide further evidence to support the hypothesis that picolinic acid facilitates absorption of dietary zinc.