|DATE||Friday, March 03|
|AUTHOR||Dr. Carlos Orozco (BSc, MSc, ND, MD, PhD, FPAMS)|
Zinc is an essential trace element for all forms of life. The significance of zinc in human nutrition and public health was recognized relatively recently. Clinical zinc deficiency in humans was first described in 1961, when the consumption of diets with low zinc bioavailability due to high phytic acid content was associated with “adolescent nutritional dwarfism” in the Middle East (1). Since then, zinc insufficiency has been recognized by a number of experts as an important public health issue, especially in developing countries (2).
Numerous aspects of cellular metabolism are zinc-dependent. Zinc plays important roles in growth and development, the immune response, neurological function, and reproduction. On the cellular level, the function of zinc can be divided into three categories: 1) catalytic, 2) structural, and 3) regulatory (3).
Nearly 100 different enzymes depend on zinc for their ability to catalyze vital chemical reactions. Zinc-dependent enzymes can be found in all known classes of enzymes (4).
Zinc plays an important role in the structure of proteins and cell membranes. A finger-like structure, known as a zinc finger motif, stabilizes the structure of a number of proteins. For example, copper provides the catalytic activity for the antioxidant enzyme copper-zinc superoxide dismutase (CuZnSOD), while zinc plays a critical structural role (4,5). The structure and function of cell membranes are also affected by zinc. Loss of zinc from biological membranes increases their susceptibility to oxidative damage and impairs their function (6).
Zinc finger proteins have been found to regulate gene expression by acting as transcriptionfactors (binding to DNA and influencing the transcription of specific genes). Zinc also plays a role in cell signalingand has been found to influence hormone release and nerve impulse transmission. Recently zinc has been found to play a role in apoptosis (gene-directed cell death), a critical cellular regulatory process with implications for growth and development, as well as a number of chronic diseases (7).
Severe zinc deficiency
Much of what is known about severe zinc deficiency was derived from the study of individuals born with acrodermatitisenteropathica, a genetic disorder resulting from the impaired uptake and transport of zinc. The symptoms of severe zinc deficiency include the slowing or cessation of growth and development, delayed sexual maturation, characteristic skin rashes, chronic and severe diarrhea, immune system deficiencies, impaired wound healing, diminished appetite, impaired taste sensation, night blindness, swelling and clouding of the corneas, and behavioral disturbances. Before the cause of acrodermatitisenteropathica was known, patients typically died in infancy. Oral zinc therapy results in the complete remission of symptoms, though it must be maintained indefinitely in individuals with the genetic disorder (5,13). Although dietary zinc deficiency is unlikely to cause severe zinc deficiency in individuals without a genetic disorder, zinc malabsorption or conditions of increased zinc loss, such as severe burns or prolonged diarrhea, may also result in severe zinc deficiency.
Mild zinc deficiency
More recently, it has become apparent that milder zinc deficiency contributes to a number of health problems, especially common in children who live in developing countries. The lack of a sensitive indicator of mild zinc deficiency hinders the scientific study of its health implications. However, controlled trials of moderate zinc supplementation have demonstrated that mild zinc deficiency contributes to impaired physical and neuropsychological development, and increased susceptibility to life-threatening infections in young children (13). For a more detailed discussion of the relationship of zinc deficiency to health problems, see Disease Prevention.
Individuals at risk of zinc deficiency:(5)
Strict vegetarians: The requirement for dietary zinc may be as much as fifty percent greater for strict vegetarians whose major food staples are grains and legumes because high levels of phytic acid in these foods reduce the absorption of zinc (4).