Zinc is an essential mineral and has a multitude of biological roles due to being a functional component of over 300 hundred enzymes. Many enzymes rely on zinc to be able to catalyze chemical reactions, and zinc participates in the structure of important proteins and is involved in the regulation of gene expression.
Oysters contain substantially more zinc than any other food, although red meat (e.g., beef, pork) and poultry provide the majority of zinc in the American diet. Other good sources of zinc are legumes, nuts, and dairy products.
The potential benefits of supplementation with zinc are largely dependent on the individual’s zinc status. That is, supplementation with zinc is unlikely to provide a benefit if zinc levels are already adequate. One exception to this rule may be in the case of respiratory tract infections, in which supplementation with zinc (in the form of lozenges) has been shown to reduce the duration of illness.
Supplementation with zinc has been shown to improve severe acne,, depressive symptoms, testosterone levels and sperm quality, and markers of glycemic control and blood lipids, particularly in people with chronic disease.
In the short term, consuming zinc in excess of the recommended upper limit (40 mg/day) can result in gastrointestinal symptoms (e.g., abominable pain, nausea, vomiting, diarrhea). In the long term, excessive zinc intake can cause copper deficiency and associated anemia, as well as suppression of the immune system. Also, the application of intranasal zinc has been reported to cause a loss of smell in some people.
The potential benefits derived from supplementation with zinc seem to be at least partly attributable to zinc’s anti-inflammatory and antioxidant properties.
Additionally, zinc is required for normal development, activity, and function of both innate and adaptive immune cells; the proper function of pancreatic beta-cells and glucose uptake; and spermatogenesis and normal sperm physiology (e.g., sperm motility).
In the brain, zinc ions inhibit N-methyl-D-aspartate (NMDA) receptors, which is relevant to depression because the condition is characterized by elevated glutamatergic neurotransmission (which NMDA receptors contribute to). Zinc may also benefit depression by increasing brain-derived neurotrophic factor levels.