Zinc is a micro-mineral usually found in meat, eggs, seafood, tofu, roasted pumpkin and squash seeds and peanuts. It is present in every body cell and is a component in over 200 enzymatic processes in the body. The Recommended Daily Amount (RDA) for zinc in the UK is 11 mg for males and 8mg for females.
Zinc is essential for protein synthesis and collagen formation. It is believed to help accelerate healing times, reduce the length and severity of colds and help restore loss of taste. Zinc has been shown to contribute to normal macronutrient metabolism, normal cognitive function and normal fertility and reproduction.
Zinc deficiency is characterized by increased susceptibility to infections, poor wound healing, reduced taste and sense of smell, growth retardation, loss of appetite and skin disorders such as acne, psoriasis and eczema. A severe deficiency may cause hair loss, diarrhoea and mental disturbances.
Immunity-The role of zinc in support of the immune system is widely acknowledged. Adequate zinc status is necessary for natural killers cell function. Individuals with inadequate zinc levels have been shown to be more susceptible to infections (1). Supplementation of zinc has been shown to provide benefit in immune system responses to bacterial and viral infections (2), (3), (4).
Cognitive Function– The claim that zinc contributes to normal cognitive function is substantiated by over 27 references under the EU Commission, 2012 (1). Maylor et al (5) was just one of the references cited which reported significant beneficial effects of zinc supplementation on cognitive function in healthy middle-aged and older adults. Zinc supplementation was also shown to be beneficial to cognitive function among school-aged urban and rural children in China (6).
Fertility and Reproduction– Zinc has been shown to play a role in reproduction in males and females (1). The process of spermatogenesis (a two stage developmental process for the production of sperm) requires zinc and it is found in abundance in seminal fluid. A diet low in zinc has been associated with low circulating concentrations of several hormones including testosterone (1). Zinc deficiency in humans Is also associated with lack of pubertal development (2), (4).
Eye Health and Macular Degeneration– There has been shown to be a positive correlation between zinc and eye health. The EU Commission 2012 (1), reports on a cause and effect relationship between the intake of zinc and maintenance of normal vision. Poor adaption to dark has been noted in those with zinc deficiency, which was shown to improve with Zinc supplementation (7). Researchers have suggested that both zinc and antioxidants delay the progression of age-related macular degeneration (AMD) and vision loss, possibly by preventing cellular damage in the retina (9), (10).
Acne- Zinc contributes to the maintenance of normal skin. Deficiencies have been linked with acne, and doctors often recommend zinc tablets as a possible treatment in severe cases. In addition, zinc contributes to normal metabolism of fatty acids, which are themselves linked with healthy skin and oil balance. Zinc also contributes to the maintenance of normal testosterone levels in the blood, and fluctuating testosterone levels are a known trigger of acne.
Colds, flu and infections- Zinc contributes to the normal functioning of the immune system. This makes it a popular supplement for those looking to ward off colds, flu and infections.
Muscle growth and repair- Zinc contributes to normal macronutrient metabolism and contributes to normal protein synthesis. Together these functions mean that zinc is important for the correct breakdown and absorption of the macronutrients- including carbohydrate and protein- and for the combination of those macronutrients into effective muscle growth. This means that those on a high protein and carbohydrate diet may want to consider a Zinc supplement as they are likely to have a higher requirement for this mineral. Zinc also contributes to the protection of cells from oxidative stress. This means it acts as an antioxidant in the protection of cells from damage related to free radicals. This may be of benefit for those participating in the exercise, as the metabolic process can produce free radical damage which may slow down recovery and repair processes.
Infertility- Zinc contributes to normal fertility and reproduction. This suggests that a zinc deficiency may be one of several factors contributing to fertility problems. In addition, Zinc contributes to the maintenance of normal testosterone levels in the blood. There is evidence that zinc deficiency is particularly damaging to sperm quality and levels in men, which may be linked with this action.
Prostate problems- Zinc contributes to the maintenance of normal testosterone levels in the blood. There is thought to be a link between testosterone and cases of benign prostatic hyperplasia (BPH), so guarding against a zinc deficiency may help to ensure testosterone levels are correctly balanced.
Zinc supplementation greater than 150mg per day has been associated with toxicity. These effects include low copper status with the potential of leading to copper-deficient anaemia, reduced levels of HDL cholesterol, reduced immune function and altered iron function. Acute adverse effects of high zinc intake include nausea, vomiting, loss of appetite, abdominal cramps, diarrhoea, and headaches. The Tolerable Upper Intake Level is 40mg for both males and females in the UK.