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What is it?
Zinc is an essential mineral that is a component of more than 300 enzymes needed to repair wounds, maintain fertility in adults and growth in children, synthesise protein, help cells reproduce, preserve vision, boost immunity, and protect against free radicals, among other functions.
Where is it found?
Good sources of zinc include oysters, meat, eggs, seafood, black-eyed peas, tofu, and wheat germ.
Why do athletes use it?*
Some athletes say that zinc
- helps boost the immune system.
- helps speed recovery between workouts.
What do the advocates say?*
In order to repair micro tears that can occur as a result of strenuous exercise, serious athletes usually require higher amounts of most vitamins and minerals—including zinc—than sedentary people.
Zinc is essential to keeping the immune system strong. For athletes, this is especially important, since being sidelined with a viral infection, or other illness, can force one to miss valuable workout time.
Zinc deficiency is problematic as plasma testosterone is regulated in part by zinc. Therefore, a zinc deficiency may adversely affect this hormone, causing muscular mass and strength to suffer. Your doctor can administer a routine test to determine whether or not you are deficient in zinc.
How much is usually taken by athletes?
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.
Are there any side effects or interactions?
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. However, using zinc nasal spray has been reported to cause severe or complete loss of smell function in at least ten people. 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 anaemia, lower levels of HDL (“good”) cholesterol, or 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 anaemia and suppression of bone marrow.17
Marginal zinc deficiency may be a contributing factor in some cases of anaemia. In a study of women with normocytic anaemia (i.e., their red blood cells were of normal size) and low total iron-binding capacity (a blood test often used to assess the cause of anaemia), combined iron and zinc supplementation significantly improved the anaemia, whereas iron or zinc supplemented alone had only slight effects.18 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.19
Zinc competes for absorption with copper, iron,20 21 calcium,22 and magnesium.23 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.24 Long-term users of NAC may consider adding supplements of zinc and copper.
Are there any drug
interactions?
Certain medicines may interact with zinc. Refer to drug
interactions for a list of those medicines.
*Athletes and fitness advocates may claim benefits for zinc based on their personal or professional experience. These are individual opinions and testimonials that may or may not be supported by controlled clinical studies or published scientific articles on zinc. For more complete and detailed information, including references and safety information, see Zinc as a nutritional supplement.
References
1. Lukaski HC. Magnesium, zinc, and chromium nutriture and physical activity. Am J Clin Nutr 2000;72:585S–93S [review].
2. Van Loan MD, Sutherland B, Lowe NM, et al. The effects of zinc depletion on peak force and total work of knee and shoulder extensor and flexor muscles. Int J Sport Nutr 1999;9:125–35.
3. Manore MM. Dietary recommendations and athletic menstrual dysfunction. Sports Med 2002;32:887–901 [review].
4. Micheletti A, Rossi R, Rufini S. Zinc status in athletes: relation to diet and exercise. Sports Med 2001;31:577–82 [review].
5. Krotkiewski M, Gudmundsson M, Backstrom P, Mandroukas K. Zinc and muscle strength and endurance. Acta Physiol Scand 1982;116:309–11.
6. Khaled S, Brun JF, Cassanas G, et al. Effects of zinc supplementation on blood rheology during exercise. Clin Hemorheol Microcirc 1999;20:1–10.
7. Chandra RK. Excessive intake of zinc impairs immune responses. JAMA 1984;252:1443.
8. Shannon M. Alternative medicines toxicology: a review of selected agents. Clin Toxicol 1999;37:709–13
9. Jafek BW, Linschoten MR, Murrow BW. Anosmia after intranasal zinc gluconate use. Am J Rhinol 2004;18:137–41.
10. Bush AI, Pettingell WH, Multhaup G, et al. Rapid induction of Alzheimer A8 amyloid formation by zinc. Science 1994;265:1464–5.
11. Potocnik FCV, van Rensburg SJ, Park C, et al. Zinc and platelet membrane microviscosity in Alzheimer’s disease. S Afr Med J 1997;87:1116–9.
12. Prasad AS. Zinc in human health: an update. J Trace Elem Exp Med 1998;11:63–87.
13. Broun ER, Greist A, Tricot G, Hoffman R. Excessive zinc ingestion-a reversible cause of sideroblastic anemia and bone marrow depression. JAMA 1990;264:1441–3.
14. Reiser S, Powell A, Yang CY, Canary JJ. Effect of copper intake on blood cholesterol and its lipoprotein distribution in men. Nutr Rep Int 1987;36:641–9.
15. Sandstead HH. Requirements and toxicity of essential trace elements, illustrated by zinc and copper. Am J Clin Nutr 1995;61(suppl):621S–24S [review].
16. Fischer PWF, Giroux A, Labbe MR. Effect of zinc supplementation on copper status in adult man. Am J Clin Nutr 1984;40:743–6.
17. Broun ER, Greist A, Tricot G, Hoffman R. Excessive zinc ingestion. A reversible cause of sideroblastic anemia and bone marrow depression. JAMA 1990;264:1441–3.
18. Nishiyama S, Irisa K, Matsubasa T, et al. Zinc status relates to hematological deficits in middle-aged women. J Am Coll Nutr 1998;17:291–5.
19. Muñoz EC, Rosado JL, Lopez P, et al. Iron and zinc supplementation improves indicators of vitamin A status of Mexican preschoolers. Am J Clin Nutr 2000;71:789–94.
20. Dawson EB, Albers J, McGanity WJ. Serum zinc changes due to iron supplementation in teen-age pregnancy. Am J Clin Nutr 1990;50:848–52.
21. Crofton RW, Gvozdanovic D, Gvozdanovic S, et al. Inorganic zinc and the intestinal absorption of ferrous iron. Am J Clin Nutr 1989;50:141–4.
22. Argiratos V, Samman S. The effect of calcium carbonate and calcium citrate on the absorption of zinc in healthy female subjects. Eur J Clin Nutr 1994;48:198–204.
23. Spencer H, Norris C, Williams D. Inhibitory effects of zinc on magnesium balance and magnesium absorption in man. J Am Coll Nutr 1994;13:479–84.
24. Brumas V, Hacht B, Filella M, Berthon G. Can N-acetyl-L-cysteine affect zinc metabolisms when used as a paracetamol antidote? Agents Actions 1992;36:278–88.
