A-Z of nutritional supplements: dietary supplements, sports nutrition foods, and ergogenic aids for health and performance: Part 46


Journal Title (Medline/Pubmed accepted abbreviation): Int. J. Sport Nutr. Exerc. Metab.
Year: 2013
Volume: 47
Page Numbers: 809-810
doi: 10.1136/bjsports-2013-092699

Summary of the review article:
Zinc
  • Zinc is an essential mineral that is critical to the function of many proteins and biological functions.
  • About 85% of zinc stores in the body are in muscle and bones; 11% is in the skin and liver; and the remaining 4% is in other tissue.
  • Excellent dietary sources of zinc include oysters, wheat germ, liver, beef, melon, squash seeds (including pumpkin seeds), and cocoa.
  • Zinc deficiency can lead to decreased testosterone, growth hormone, and insulin-like growth factor 1 (IGF-1). Supplementation with zinc can restore concentrations of these biological hormones.
  • Supplementation with zinc in people that have healthy zinc stores does not augment sports performance.
  • Supplementation with more than 100 mg/day of zinc can cause adverse side effects including headache, cramps, nausea, and copper deficiency.

Zinc monomethionine aspartate (ZMA)
  • ZMA is marketed to athletes that experience zinc or magnesium deficiencies, but is becoming popular among many athletes.
  • ZMA supplementation has been shown to increase zinc stores, magnesium stores, circulating testosterone, and IGF-1. However, these observations were only reported in one study. Three other studies with similar supplementation protocols saw no response of ZMA supplementation.
  • There are claims that ZMA may improve the quality of sleep, but to date there are not any studies that have investigated this claim.

 
Key practice applications: Zinc supplementation can improve performance when a person is deficient in zinc, though it does not appear to be beneficial in individuals that are replete in zinc stores. If you are feeling weak or have a diet that is low in meat and animal products, you should have your zinc status evaluated and may benefit from a supplementation regimen.
ZMA has become a popular supplement, though there are very few studies investigating its effects. There is only one study to date that has shown performance benefits, and the article does not state whether these athletes were deficient in zinc or magnesium before the supplementation period.
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