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Zinc
Zinc:
Zinc is an essential trace mineral that has functions as part of about 300 different enzymes. As such, zinc plays a role in virtually all biochemical pathways and physiological processes. More than 90% of the body’s zinc is stored in the bones (30%) and muscles (60%), but zinc is also found in virtually all body tissues. The richest dietary sources of zinc are seafood (especially oysters), meat, fish, eggs, and poultry.
Theory Because zinc is an essential part of nearly 300 different biochemical pathways, structure/function claims can be made for the nutrient’s role in a wide variety of processes including digestion, wound healing, energy production, growth, cellular repair, collagen synthesis, bone strength, cognitive function, carbohydrate metabolism (glucose utilization and insulin production), and reproductive function. Even mild zinc deficiency has been associated with depressed immunity, decreased sperm count and impaired memory. Perhaps the most popular claim for zinc lately is for its role in immunity, where zinc may interfere with the replication of the cold virus (rhinovirus).
There is certainly sufficient evidence supporting the use of zinc lozenges in reducing the duration and severity of colds. Although concentrated zinc lozenges can help kill cold viruses in the mouth and throat, it is important to begin using them as soon as possible following the onset of cold symptoms (ideally within the first 24-48 hours). Test tube studies have shown that zinc can block the cold virus from replicating – and effect that could help the body’s natural immune defenses "get a jump on" killing the viruses. Most studies of the effect of zinc lozenges (typically zinc gluconate or zinc acetate) on the common cold have shown that subjects in the supplement group tend to have fewer "symptomatic" days (on average 2-3 fewer sick days) compared to subjects receiving a placebo (measured in terms of coughing, sore throat, nasal congestion and headache). Occasionally, high dose zinc supplements are recommended to diabetic patients. Such patients commonly suffer from increased loss of zinc and reduced body stores of zinc. High doses of zinc have been shown to mimic the effects of insulin in reducing blood sugar and promoting wound healing. These effects, however, should be considered preliminary and high dose zinc supplements are not recommended for diabetics except on the advice of their personal physician. Exercise performance has also been associated with adequate zinc status – especially in athletes who avoid red meat, concentrate their diets too much on carbohydrates or follow an overly restricted dietary regime. Low zinc intake (3mg/day) has been linked to reduced activity of a zinc-containing enzyme in red blood cells called carbonic anhydrase (which helps red blood cells transport carbon dioxide from tissues to the lungs to be exhaled). Mild to moderate zinc deficiency can lead to significant reductions in ability to take up and use oxygen, remove carbon dioxide and generate energy during high intensity exercise. Zinc has also been linked to enhanced bone formation and reduction of bone loss – both alone and in combination with plant isoflavones such as genistein. When used together with isoflavones, it appears that the isoflavonoid effect on bone is enhanced by zinc and may have a potent role in prevention of bone loss.
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