This chapter discusses the importance of zinc in human nutrition. Zinc is an essential trace element for humans, animals, and plants. It is vital for many biological functions and plays a crucial role in more than 300 enzymes in the human body. The adult body contains about 2–3 grams of zinc. Zinc is found in all parts of the body: it is in organs, tissues, bones, fluids, and cells. Muscles and bones contain most of the body's zinc. Particularly, high concentrations of zinc are in the prostate gland and semen. Zinc is generally less available from foods of plant origin than from foods of animal origin. The calculated zinc requirements for infants indicate that zinc in human milk should be highly available for absorption if requirements are to be satisfied. Observations on infants and animals have shown that zinc is substantially less available from cow milk than from human milk.
The objective of this paper is to provide a current overview of the significance of zinc in human nutrition. To achieve this, the following issues are addressed: (1) the biochemistry and biology of zinc in the context of their relevance to zinc in human nutrition and to our understanding of the complexity and practical importance of human zinc deficiency; (2) the history of our understanding of human zinc deficiency with an emphasis both on its brevity and on notable recent progress; (3) the clinical spectrum of severe zinc deficiency; (4) the lack of ideal biomarkers for milder zinc deficiency states, with the consequent dependence on randomized, placebo-controlled intervention studies to ascertain their prevalence and clinical consequences, including growth delay, diarrhea, pneumonia, other infections, disturbed neuropsychological performance and abnormalities of fetal development; (5) the public health significance of human zinc deficiency in the developing world; (6) reasons for concern and unanswered questions about zinc nutriture in the United States; (7) the need for better understanding of human zinc metabolism and homeostasis (including its limitations) at a molecular, cellular, organ-system and whole body level and of factors that affect zinc bioavailability; and (8) potential strategies for the prevention and management of human zinc deficiency. This review concludes with an emphasis on the immediate need for expanded research in directions that have become increasingly well demarcated and impelling as a result of recent progress, which is summarized in this overview.