Zinc is an essential mineral that is naturally present in a wide variety of food from plant and animal origins. It plays an important role in growth and development, taste, smell, wound healing, immune function, protein synthesis, and the maintenance of skin and hair.
Deficiency in zinc is common in older people and is associated with risk factors such as age (over 65 years), renal disease, chronic gastrointestinal disease, and chronic liver disease.
Zinc Deficiency and Increased Susceptibility to Infection
People with zinc deficiency experience increased susceptibility to a variety of pathogens. This is not surprising, as zinc is crucial for the function of immune cells that act at every level of the immune response including neutrophils, natural killer cells, T lymphocytes, and B lymphocytes .
For instance, several studies showed that zinc supplementation reduces the incidence of acute and chronic diarrhea and acute lower respiratory infections .
Zinc Deficiency and Delayed Wound Healing
Zinc concentration is high in the epidermis of the skin and its deficiency was shown to lead to roughened skin and impaired wound healing. Zinc is essential during the different phases of wound healing, such as clot formation, inflammation, cell proliferation, re-epithelialization, granulation, angiogenesis, matrix remodeling, and scarification .
Zinc Deficiency and Maintenance of the Skin and Hair
Zinc is required for the active proliferation and differentiation of epidermal keratinocytes. However, zinc requires the activity of the zinc transporter ZIP4 that acts as a zinc sensor. Mutations in ZIP4 result in zinc deficiency and a disorder known as acrodermatitis enteropathica that is characterized by alopecia (hair loss), diarrhea, and skin lesions .
Zinc Deficiency and Loss of Taste and Smell
Several studies reported a taste disfunction in some patients who were given drugs that altered zinc metabolism or who experienced disease processes associated with abnormalities of zinc metabolism.
Consequent studies have shown that zinc plays a role in regulating the function of the taste bud, the nerves that transmit taste information to the brain. Interestingly, the treatment of these patients with zinc produced improvement in taste function .
Zinc deficiency is responsible for several disorders that can lead to increased infections and delayed would healing that results in serious consequences on the health of affected people. Several studies have shown that these disorders could be reversed through direct zinc supplementation or via its consumption through a diet rich in zinc.
 Sazawal, S., Black, R.E., Bhan, M.K., Jalla, S., Bhandari, N., Sinha, A. and Majumdar, S., 1996. Zinc supplementation reduces the incidence of persistent diarrhea and dysentery among low socioeconomic children in India. The Journal of nutrition, 126(2), pp.443-450.
 Ruel, M.T., Rivera, J.A., Santizo, M.C., Lönnerdal, B. and Brown, K.H., 1997. Impact of zinc supplementation on morbidity from diarrhea and respiratory infections among rural Guatemalan children. Pediatrics, 99(6), pp.808-813.
 Sazawal, S., Black, R.E., Jalla, S., Mazumdar, S., Sinha, A. and Bhan, M.K., 1998. Zinc supplementation reduces the incidence of acute lower respiratory infections in infants and preschool children: a double-blind, controlled trial. Pediatrics, 102(1), pp.1-5.