Zinc

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 glands^{1, 2}.

Second only to iron in terms of the amount we have in our bodies, Zinc is an essential mineral for growth, development, and maintaining health. Not only is it a structural constituent of many organs, including kidneys, bones, testes, prostate gland, and muscles, which contain over 50% of the body's zinc, but it is necessary part of more than 300 enzymatic reactions that occur within the body.

Zinc is a mineral with a lot of benefits, and it has been studied extensively for its role in supporting the immune system. It is commonly used in the prevention and treatment of colds, skin conditions, and common infections. This mineral also has an important role in the regulation of testosterone production, and a zinc deficiency can impede the body's production of this anabolic male hormone. A good zinc level is therefore important for male fertility and for anyone trying to build muscle. Zinc is an essential mineral which means we must take it in through food, and it is found abundantly in seafood, meat, dairy, and many vegetables, cereals and legumes. It's not always easy for busy people to eat a varied diet, and a zinc supplement is a convenient way to fight sickness, ensure ongoing health and optimise muscle growth.

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.

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.

Zinc Benefits

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 cold^{6, 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 indication^{16, 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.

Zinc Supplements

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.

Stacking Zinc

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.
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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.
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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.