Zinc is an essential trace element and serves as the active center of approximately 300 enzymes. Therefore, zinc deficiency may be associated with a variety of clinical features such as hypogeusia, hyposmia, growth retardation, dermatitis, alopecia, gonadal hypofunction, abnormal pregnancy, susceptibility to infections, delayed wound healing, impaired glucose tolerance, and increased carcinogenesis. Zinc deficiency was reported to be on the increase in the Nagano Study conducted from 2003 to 2005. Zinc therapy is classified into two categories, zinc-supplementary and -specific treatments. Ordinarily, zinc-supplementary therapy is carried out for the symptoms and diseases caused by zinc deficiency. On the other hand, zinc-specific therapy is applied to obtain copper- and iron-chelating, antifibrotic, and antidiabetic effects. The availability of zinc-specific therapy is now confirmed in humans and animals. Hereafter, the safety of zinc therapy needs to be examined further.