ZINC
Stimulates hair and nail growth. Aids in
preventing hair loss. May help treat and prevent
dandruff.
Zinc
(Zn) is an essential trace mineral. The human body has between 1.5 - 2.5 g
Zn, making it nearly as abundant as iron. It is highly concentrated in
specialized areas of the brain, pancreas and adrenal gland, but is present
in all cells, particularly in the nucleus. Zinc has structural, catalytic
(enzymatic) and regulatory roles. About 1% of the human genome codes for
zinc finger proteins, where zinc provides a structural role for regulatory
functions. Over 60 enzymes require zinc for activity, including the RNA
polymerases. Zinc is actively taken up by synaptic vesicles, supporting a
role in neuronal activity and memory. Zinc metabolism is altered during
disease and physical stress through hormones, cytokines and toxins,
presumably as part of a host defense response.
IMPORTANCE: Is an antioxidant nutrient; necessary
for protein synthesis; wound healing; vital for the development of the
reproductive organs, prostate functions and male hormone activity; it
governs the contractility of muscles; important for blood stability;
maintains the body's alkaline balance; helps in normal tissue function;
aids in the digestion and metabolism of phosphorus.
Deficiencies: An early sign of zinc deficiency in
animals is decreased food intake. It is a type II deficiency since a
reduction in growth occurs without an apparent reduction in tissue zinc.
Reduced immune function, involving B cell and T cell depletion and/or
reduced activity, and skin lesions associated with secondary infections
are common findings. Chronic zinc deficiency in humans results in reduced
growth (dwarfism) and sexual development which are reversible by raising
zinc intake. Signs of zinc deficiency may reflect its involvement in cell
proliferation and differentiation. Growth, behavioral abnormalities and
cognition may respond to zinc supplementation in some populations. Many
clinical findings that relate to depressed growth or immunity may have
marginal zinc deficiency as a secondary cause. May result
in delayed sexual maturity, prolonged healing wounds, white spots on
finger nails, retarded growth, stretch marks, fatigue, decreased
alertness, susceptibility to infections.
Clinical uses: Zinc is not widely used as a
therapeutic agent except as an ingredient of topical medication. Oral zinc
may be used to treat idiopathic skin lesions, some inflammatory conditions
and depressed immunity. Zinc is usually indicated in rehabilitation
therapy from malnutrition and/or malabsorption in children and adults,
used in feeding programs for premature infants and neonates and is also a
component of TPN solutions. Supplemental zinc reduces acute diarrhea and
depressed immunity.
Diet recommendations: The Recommended Dietary
Allowances (RDAs) are: infants, 5 mg/day; children <10 years, 10
mg/day; males >10 years, 15 mg/day; females >10 years, 12 mg/day;
pregnancy, 15 mg/day; and lactation, 0-6 mo., 19 mg/day; 7-12 mo., 16
mg/day.
Food sources: Zinc is highly abundant in red and white
meat and shellfish. Foods of plant origin except the embryo portion of
grains, e.g., wheat germ, are low in zinc. Phytic acid in plants like
soybeans binds zinc, forming an insoluble complex that lowers
bioavailability. Other inhibitors of absorption are fiber, polyphenols and
a high intake of calcium. Zinc from human milk is more absorbable than
that from infant formulas or cow's milk.
Toxicity: Acute zinc toxicity is characterized by
gastric distress, dizziness and nausea. Symptoms of chronic toxicity
include gastric problems, decreased serum ceruloplasmin activity and
hypocupremia, decreased lymphocyte stimulation to PHA and reduced HDL
cholesterol. An emetic effect occurs at >150 mg Zn/day. Consumption of
zinc supplements produces measurable cellular effects but the long term
benefit/risk of zinc supplementation has yet to be determined.
Recent research: Experiments with transgenic and knock
out mice are defining the role for zinc metalloproteins in metabolism,
development and cytoprotection. Zinc as a component of an antioxidant
system is being evaluated. Zinc as a factor in Ab amyloid protein
aggregation leading to plaque formation found in Alzheimer's patients is
under investigation. Supplemental zinc has been proven to be of benefit in
treatment of acute diarrhea in infants and children. Fluorescent zinc
indicators are in use to define zinc functions at the cellular level.
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