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Exercise increases zinc losses from the human body, and severe zinc deficiency can compromise muscle function.1, 2 Athletes who do not eat an optimal diet, especially those who are trying to control their weight or use fad diets while exercising strenuously, may become deficient in zinc to the extent that performance or health is compromised.3, 4. One double-blind trial in women found that 135 mg per day of zinc for two weeks improved one measure of muscle strength.5 Whether these women were zinc deficient was not determined in this study. A double-blind study of male athletes with low blood levels of zinc found that 20 mg per day of zinc improved the flexibility of the red blood cells during exercise, which could benefit blood flow to the muscles.6 No other studies of the effects of zinc supplementation in exercising people have been done. A safe amount of zinc for long-term use is 20 to 40 mg per day along with 1 to 2 mg of copper. Higher amounts should be taken only under the supervision of a doctor.
Zinc intake in excess of 300 mg per day has been reported to impair immune function.7 Some people report that zinc lozenges lead to stomach ache, nausea, mouth irritation, and a bad taste. One source reports that gastrointestinal upset, metallic taste in the mouth, blood in the urine, and lethargy can occur from chronic oral zinc supplementation over 150 mg per day,8 but those claims are unsubstantiated. In topical form, zinc has no known side effects when used as recommended.
Caution: Using zinc nasal spray has been reported to cause severe or complete loss of smell function. In some of those cases, the loss of smell was long-lasting or permanent.9
Preliminary research had suggested that people with Alzheimer’s disease should avoid zinc supplements.10 More recently, preliminary evidence in four patients actually showed improved mental function with zinc supplementation.11 In a convincing review of zinc/Alzheimer’s disease research, perhaps the most respected zinc researcher in the world concluded that zinc does not cause or exacerbate Alzheimer’s disease symptoms.12
Zinc inhibits copper absorption. Copper deficiency can result in anemia, lower levels of HDL (“good”) cholesterol, neurological disorders, and cardiac arrhythmias.13, 14, 15 Copper intake should be increased if zinc supplementation continues for more than a few days (except for people with Wilson’s disease).16 Some sources recommend a 10:1 ratio of zinc to copper. Evidence suggests that no more that 2 mg of copper per day is needed to prevent zinc-induced copper deficiency. Many zinc supplements include copper in the formulation to prevent zinc-induced copper deficiency. Zinc-induced copper deficiency has been reported to cause reversible anemia and suppression of bone marrow.17 In addition, there are case reports of neurologic abnormalities due to copper deficiency occurring in people who had been using large amounts of certain widely available denture creams that contained high concentrations of zinc.18
In a study of elderly people with macular degeneration, supplementing with 80 mg of zinc per day for an average of about six years increased by about 50% the incidence of hospitalizations due to genitourinary causes (such as urinary tract infections, kidney stones, and urinary retention).19 In that study, copper was also given, but in a form that cannot be absorbed by humans (cupric oxide). The reported adverse effect of zinc may have been due in large part to zinc-induced copper deficiency, which could be prevented by taking copper in a form other than cupric oxide. Nevertheless, it would be prudent for elderly people wishing to take large amounts of zinc to consult with a doctor.
Marginal zinc deficiency may be a contributing factor in some cases of anemia. In a study of women with normocytic anemia (in other words, their red blood cells were of normal size) and low total iron-binding capacity (a blood test often used to assess the cause of anemia), combined iron and zinc supplementation significantly improved the anemia, whereas iron or zinc supplemented alone had only slight effects.20 Supplementation with zinc, or zinc and iron together, has been found to improve vitamin A status among children at high risk for deficiency of the three nutrients.21
Zinc competes for absorption with copper, iron,22, 23calcium,24 and magnesium.25 A multimineral supplement will help prevent mineral imbalances that can result from taking high amounts of zinc for extended periods of time.
N-acetyl cysteine (NAC) may increase urinary excretion of zinc.26 Long-term users of NAC may consider adding supplements of zinc and copper.
Certain medicines interact with this supplement.
|Replenish Depleted Nutrients|
|Reduce Side Effects|
|Potential Negative Interaction|
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The information presented by Healthnotes is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. Self-treatment is not recommended for life-threatening conditions that require medical treatment under a doctor's care. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires December 2017.