In more recent years, much interest has been generated by the possibility that subclinical zinc deficiency may significantly increase the incidence of and morbidity and mortality from diarrhea and upper respiratory tract infections. Along with iron, iodine, and vitamin A, zinc deficiency is one of the most important micronutrient deficiencies globally. 
Meat and chicken are excellent sources of zinc, as are nuts and lentils. In the Western diet, food products such as breakfast cereal are fortified with zinc and these products provide an increasingly important source of zinc. Approximately 45 percent of adults may have inadequate zinc intakes. 
It has important roles both in cell division as well as apoptosis (programmed cell death) and thus plays a role in growth, tissue repair, and wound healing. It is also involved in lipid and glucose metabolism and in immunity and the response to infection. Zinc deficiency is associated with impaired phagocytic function, lymphocyte depletion, decreased immunoglobulin production, reduction in the T4+/T8+ ratio, and decreased interleukin 2 (IL-2) production. 
Mild dietary zinc deficiency impairs growth velocity while severe depletion of zinc leads to growth failure. Other clinical manifestations of zinc deficiency include delayed sexual maturation, impotence, hypogonadism, oligospermia, alopecia, dysgeusia (impaired taste), immune dysfunction, night blindness, impaired wound healing, and various skin lesions. 
Humans are very tolerant of high zinc intakes up to 100 mg/day. Mega-dose supplementation or high zinc intake from contaminated food or beverages has been associated with nonspecific gastrointestinal symptoms, including abdominal pain, diarrhea, nausea, and vomiting. Zinc may interfere with copper absorption, and high zinc intakes (>150 mg/day) can lead to copper deficiency.