Zinc as an Appetite Stimulator - The Possible Role of Zinc in the Progression of Diseases Such as Cachexia and Sarcopenia

Zinc is required by humans and animals for many physiological functions, such as growth, immune function, and reproduction. Zinc deficiency induces a number of physiological problems, including anorexia, growth retardation, dermatitis, taste disorder, and hypogonadism. Although it is clear that zinc deficiency produces specific and profound anorexia in experimental animals, the connection between zinc deficiency and anorexia is less certain. We were the first to show that orally, but not intraperitoneally, administered zinc rapidly stimulates food intake through orexigenic peptides coupled to the afferent vagus nerve using rats during early-stage zinc deficiency without decreased zinc concentrations in plasma and tissues. We confirmed that a zinc-sufficient diet containing zinc chloride acutely stimulated food intake after short-term zinc deprivation. We also found that orally administered zinc sulfate increased the expression of NPY and orexin mRNA after administration. Using vagotomized rats, we tested whether the increase in food intake after oral administration of zinc was mediated by the vagus nerve. In sham-operated rats, the oral administration of zinc stimulated food intake, whereas zinc and saline administrations did not exhibit differing effects in vagotomized rats. We conclude that zinc stimulates food intake in short-term zinc-deficient rats through the afferent vagus nerve with subsequent effects on hypothalamic peptides associated with food intake regulation. In this review, we describe recent research investigating the roles of zinc as an appetite stimulator in food intake regulation, along with research about hypothalamus, ghrelin, leptin and zinc receptor, and clinical application about anorexia nervosa, cachexia and sarcopenia. The article also presents some promising patents on zinc.