Zinc is essential for many metabolic and enzymatic functions in man. Deficiency of
zinc in man has now been recognized to occur not only as a result of nutritional factors, but also in various disease states, including
malabsorption syndromes,
acrodermatitis enteropathica,
Crohn's disease,
alcoholism and
cirrhosis of the liver. The deficiency state in human subjects exists as a spectrum extending from mild to severe degree. The clinical manifestations of mild
zinc deficiency include
oligospermia,
weight loss and hyperammonaemia. Moderate
zinc deficiency is characterized clinically by growth retardation,
hypogonadism in males, skin changes, poor appetite, mental
lethargy, delayed wound healing, taste abnormalities and abnormal dark adaptation. In severe
zinc deficiency states, bullous-pustular
dermatitis,
alopecia, diarrhoea, emotional disorders,
weight loss, intercurrent
infections,
hypogonadism in males and, if unrecognized, death have been observed.
Zinc is needed for the functions of over 100
enzymes. It is essential for
DNA,
RNA and
protein synthesis and, as such, is important for cell division.
Zinc is an inducer of
mRNA of
metallothionein, a protein which may have an important role in the regulation of intestinal
zinc absorption.
Zinc has a specific effect on testes in animals and man. Recent reports indicate that in human subjects
thymopoietin may be
zinc dependent and in animal studies
somatomedin may be affected adversely due to dietary
zinc restriction.
Zinc plays an important role in the protection of cell membrane integrity and may be protective against
free radical injury.
Zinc is known to compete with
cadmium, lead,
copper,
iron and
calcium for similar binding sites. In the future, a potential use of
zinc may be to alleviate toxic effects of
cadmium and lead in human subjects. Recent evidence suggests that thymic-dependent lymphocytes (T cells are
zinc dependent. T-helper and suppressor cells, T-effector cells and T-natural killer cells appear to be
zinc dependent.
Zinc is also essential for some of the neutrophil functions. Thus, it appears that
zinc may play an important role in immunity. One may suggest that some of the clinical features of
cirrhosis of the liver, such as testicular
atrophy, loss of body hair,
night blindness, poor wound healing, poor appetite, susceptibility to
infections and enhanced sensitivity to drugs, may be related to conditioned deficiency of
zinc, future studies are required to determine whether or not
zinc supplementation is beneficial to these patients.