What is Zinc?
In chemical gobbledygook, zinc is a divalent trace element. It layman terms, it’s an important essential mineral necessary for growth and development. Zinc is a cofactor for over 300 known enzymes and out of all the minerals, it is second only to iron in body content at 2 to 3 g4. As well as being a cofactor for many enzymes, zinc is an important structural constituent for many proteins in the body. Half of the body’s total zinc is present in muscle2. Other major organs of the body that contain zinc include bones, skin, kidneys, testes, and prostate glands1, 2.
Where Does Zinc Come From?
Classified as an essential mineral, zinc can only be obtained from dietary sources. Below is a table listing the major sources of dietary zinc1.
Category of Foods
Examples of Foods
Flesh of shellfish, shrimp, lobster, crab
Organs and flesh of mammals and fowl
Liver, meat, or muscle
Whole grain cereal, vegetables
Chickpeas, kidney beans, almonds
Yogurt, milk, cheese
Interestingly, zinc absorption has been shown to increase with increasing protein intake in a given meal3. This is thought to be due to the release of amino acids such as histidine, methionine and cysteine during digestion of the protein3.
Because it is involved in a wide range of bodily functions, the possible benefits of zinc supplementation have been studied for a large number of conditions and symptoms. Some of the most commonly cited indications for zinc supplementation include common infections (ear infection5, common cold6, 7, diarrhea8), various skin lesions9, diabetic complications10, alzheimer’s disease11 and macular degeneration12. Another very common association with zinc supplementation is an increase in taste sensitivity and appetite. The sense of taste is mediated through the salivary zinc-dependent polypeptide, known as gustin13. Studies have shown that low salivary zinc concentration leads to a reduction of taste and reduced appetite13. Lastly, zinc is commonly indicated to help increase/normalise testosterone levels. However, there is conflicting research on this particular indication16, 17.
Negative Side Effects of Zinc
One of the main complications of excess zinc intake is that it interferes with copper absorption18. Supplementation with zinc at 2 g/d and above can lead cause GI symptoms and vomiting4. More serious consequences of zinc toxicity include anemia, fever and central nervous system effects18.
Zinc Recommended Dosages & Timing
Zinc is usually supplemented in amounts ranging from 15-50mg. There is no particular advice concerning the timing of zinc supplementation.
In bodybuilding supplements, zinc most commonly features as part of a complex called 'zma'. This complex consists of zinc monomethionine aspartate, magnesium aspartate and vitamin B619. As discussed in our magnesium article, this particular complex was shown to increase strength and muscle mass by one particular group of researchers19. However, the findings have yet to be replicated by any other group of researchers20. This has raised the question of the validity of the original study; especially given that the same company who patented the original zma complex also sponsored the original study20. Aside from zma, zinc oxide and zinc sulfate are two of the most popular forms of oral zinc used in studies. Other forms include zinc glycinate, zinc monomethionine, zinc histidine, zinc picolinate, zinc citrate, zinc gluconate, zinc amino acid chelate and zinc carnosine. Zinc carnosine is a unique form of zinc that has been shown to have therapeutic actions not normally associated with other forms of zinc. In Japan, zinc carnosine is sold under the trade name of Polaprezinc® and is approved for treatment of gastric ulcers14. In a study comparing the bioavailability of different forms of zinc, zinc carnosine was shown to have the highest bioavailability15.
Because of its potential to interfere with copper absorption, small amounts of copper are often found in zinc-containing supplements. Additionally, because of zinc purported role in optimising testosterone levels, it is often stacked with other testosterone boosting supplements or ingredients. As mentioned above, zinc is often sold as part of a complex called 'zma', however, many companies feature a combination of zinc, magnesium and vitamin B6, but include different forms of zinc and magnesium. Such forms are typically cheaper than those used in the original zma complex. Because the original study on zma showed increased growth hormone release, zinc or the zma-complex commonly feature in human growth hormone stimulating products.
1.Standing committee on the Scientific Evaluation of Dietary Reference Intakes, Institute of Medicine (US). Zinc. In: Dietary References Intakes for Vitamin A, Vitamin K, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington DC: National Academy Press; 2000:442-501.
2. Rahman, MT. (2011). Dietary Zinc and the Brain. In Preedy VR, Watson RR & Martin CR (Eds.), Handbook of Behaviour, Food and Nutrition (pp. 2357-2373). New York: Springer.
3. Lonnerdal B. Dietary factors influencing zinc absorption. The Journal of Nutrition. 2000;130:1378S-1383S.
4. Lord RS & Bralley JA. (2008). Laboratory Evaluations for Integrative and Functional Medicine. Metametrix Institute.
5. Gulani A, Sachdev HS. Zinc supplements for preventing otitis media. Cochrane Database Syst Rev. 2012 Apr 18;4:CD006639.
6. Maggini S, et al. A combination of high-dose vitamin C plus zinc for the common cold. J Int Med Res. 2012;40(1):28-42.
7. Kartasurya MI, et al. Zinc combined with vitamin A reduces upper respiratory tract infection morbidity in a randomised trial in preschool children in Indonesia. Br J Nutr. 2012; 1-10.
8. Bajait C & Thawani V. Role of zinc in pediatric diarrhea. Indian J Pharmacol. 2011;43(3):232-235.
9. Kumar P, et al. Zinc and skin: A brief summary. Dermatol Online J. 2012;18(3):1.10.
10. Jayawardena R, et al. Effects of zinc supplementation on diabetes mellitus: a systematic review and meta-analysis. Diabetol Metab Syndr. 2012;4(1):13.
11. Craddock TJ, et al. The zinc dyshomeostasis hypothesis of Alzheimer's disease. PLoS One. 2012;7(3):e33552.
12. Moriarty-Craige SE, et al. Effects of long-term zinc supplementation on plasma thiol metabolites and redox status in patients with age-related macular degeneration. Am J Ophthalmol. 2007;143(2):206-211.
13. Shatzman AR, Henkin RI. Gustin concentration changes relative to salivary zinc and taste in humans. Proc Natl Acad Sci U S A. 1981 Jun;78(6):3867-71.
14. Takei M. The development of polaprezinc research. Yakugaku Zasshi. 2012;132(3):271-277.
15. Matsukura T & Tanaka H. Applicability of zinc complex of l-carnosine for medical use. Biochemistry. 2000;65(7):817-823.
16. Prasad AS, et al. Zinc status and serum testosterone levels of healthy adults. Nutrition. 1996;12(5):344-348.
17. Koehler K, et al. Serum testosterone and urinary excretion of steroid hormone metabolites after administration of a high-dose zinc supplement. Eur J Clin Nutr. 2009;63(1):65-70.
18. Maret W & Sandstead HH. Zinc requirements and the risks and benefits of zinc supplementation. J Trace Elem Med Biol. 2006;20(1):3-18.
19. Brilla LR, Conte V. Effects of a novel zinc-magnesium formulation on hormones and strength. JEPOnline. 2000;3(4):26-36.
20. Wilborn CD, Kerksick CM, Campbell BI, et al. Effects of zinc magnesium aspartate (ZMA) supplementation on training adaptations and markers of anabolism and catabolism. Journal of the International Society of Sports Nutrition. 2004;1(2):12-20.