2009 年 20 巻 4 号 p. 284-295
Zinc deficiency is worldwide and one of the most important public health problems in the world. This review contains a concise history of the discovery of human zinc deficiency to promote understanding of the importance of zinc kinetics, and the further methodological development of zinc kinetic analysis using radioisotopes and stable isotopes with a special emphasis on the estimation of the critical value for plasma zinc in humans. A brief history of diagnosis of iron deficiency is also discussed, because zinc and iron nutriture was revealed to be associated in humans due to the common food factors. Based on nonlinear regression analysis with a broken-line model of the relationship between plasma zinc and the lesser peripheral zinc pool size, candidates of the critical value for plasma zinc were proposed. After the scientific evaluation by the Nutrition and Toxicity Evaluation Committee, Japan Society for Biomedical Research on Trace Elements formed in 2008 a diagnostic criterion for human zinc deficiency : 80 µg/dL of plasma or serum zinc as a lower limit of normal zinc status at the condition of the forenoon collection. Co-occurrence of mild deficiencies of iron and zinc was discovered from young American women using zinc kinetic analysis as a survey tool. The co-occurrence was explained by the common food factors : beef or red meat as a common source of bioavailable iron and zinc, and bran breakfast cereals as a source of phytate, a potent absorption inhibitor for both iron and zinc. Menorrhagia (heavy menstrual blood loss) as detected by bleeding through menstrual pads was a negative predictor for both iron and zinc nutriture for women. Although vitamin C is a potent enhancer of iron absorption, several studies including zinc kinetic analysis found that excessive vitamin C may impair zinc status by a potential inhibition of zinc absorption through complexation with zinc. Overall, outcomes of zinc kinetic studies are expected to contribute to understanding of zinc nutrition and metabolism and to treatment of zinc deficiency in humans.
