Zinc is a trace element and an essential component of good nutrition. Many of us have seen zinc when it is used to coat steel to protect against corrosion—like that old trash can where Oscar the Grouch lives. Zinc works as a co-factor and is required to facilitate the activity of over 300 enzymes in our bodies. Zinc plays a key role in carbohydrate, fat and protein metabolism. The enzyme superoxide dismutase requires Zinc in order to protect against free radical damage. Immune system function is also bolstered by Zinc. Obviously these roles are important to everybody, and they are even more important to endurance athletes trying to balance the stresses of training and racing with those of recovery.
Endurance athletes are at risk for being zinc deficient. Several studies have shown athletes to be deficient in Zinc.1 2 3 Athletes may be at risk for Zinc deficiency both through inadequate dietary intake and through losses that occur with high intensity and long duration exercise. Athletes can lose up to 9% of the US RDA for Zinc in a single 2 hour training session.4 Vitamin B6 depletion may also play a role in decreased zinc and magnesium serum levels. Some of the roles of magnesium have been discussed in our previously posted Energy and Electrolyte Considerations as well as in A Tale of Five Electrolytes. Magnesium deficiency, like zinc, has been shown to result in decreased strength as well as decreased exercise endurance
We have previously discussed Cortisol and Overtraining Syndrome: Why an Athlete Should Care. There is compelling evidence to suggest that Zinc supplementation can decrease cortisol levels5. When Zinc is replete, anabolic hormones such as testosterone and insulin-like growth factor-1 (IGF-1) actually increase. This is very exciting news for athletes suffering from chronically elevated cortisol levels. IGF-1 is a hormone that promotes recovery and rebuilding of lean tissue in adults, and increases growth rates in children. Zinc and magnesium deficiencies are associated with growth retardation in children. Repleting zinc and magnesium has lead to a 70% increase in IGF-1 and restoration of growth rates for those same children. For athletes, IGF-1 is a key recovery hormone. A study using rats demonstrated a 60% or 80% decrease in IGF-1 when the animals were deprived of magnesium and zinc, respectively. When zinc and magnesium levels were repleted, IGF-1 levels increased 194%6
While the effects of zinc and magnesium in rats are interesting, we are more interested in what these elements can do for the human athlete. A study of the effects of zinc-magnesium preparation combined with vitamin B6 has been done7. A double-blind, randomized, controlled study was conducted using ZMA (30mg zinc monomethionine aspartate, 450mg magnesium aspartate, and 10.5mg of vitamin B6). In this study a group of college football players were given ZMA nightly for a period of 8 weeks during spring football training. Zinc, Magnesium, Testosterone and IGF-1 levels were measured and strength was tested both before and after the supplement period. The placebo group exhibited significantly decreased levels of Zinc, Magnesium, Testosterone and IGF-1, while the supplemented group demonstrated significantly increased levels of the same. Why does this matter? The supplemented group also exhibited leg torque and power increases of approximately 10%, which was statistically significant compared to controls. While a subsequent study8 was not able to support these results, the athletes the subsequent study had normal zinc and magnesium levels before and after the study period, which may explain the lack of performance increases.
Training, competing, and everyday life stress athletes. In the absence of adequate zinc and magnesium, these stresses can have catabolic rather than anabolic effects. Much like a healthy dose of zinc can protect steel from corrosion; athletes should protect their bodies from catabolism. A bioavailable supplement of zinc and magnesium, like ZMA, is recommended.
1Zalcman I, Guartita HV, et al. Nutritional status of adventure racers. Nutrition. 2007 May;23(5): 404-11.
2 Singh A, smoak BL, Patterson KY, et al. Biochemical indice of selected trace minerals in men: effect of stress. Am J Coin Nutr. 1991;53: 126-31.
3 Cordova A, Navas FJ. Effect of training on zinc metabolism: changes in serum and sweat zinc concentrations in sportsmen. Ann Nutr Metab. 1998;42: 274-82.
4 DeRuisseau KC, Chevront SN, Haymes EM, Sharp RG. Sweat iron and zinc losses during prolonged exercise. Int J Sport Nutr Exerc Metab. 2002 Dec;12(4): 428-37.
5 Golf SW, Bender S, Gruttner J. On the significance of magnesium in extreme physical stress. Cardiovasc Drugs Ther 1998: 12:197-202.
6 Droup I, Flyvbjerg A, Everts ME, Clausen T. Role of insulin-like growth factor-1 and growth horomone in growth inhibition induced by magnesium and zinc deficiencies. BrJ Nutr 1991: 66:505-21.
7 Billa LR, Conte V. effects of a Novel Zinc-Magnesium Formulation on Hormones and Strength. JEPonline, 3(4): 26-36, 2000.
8 Wilborn CD, Kersick CM, et al. Effects of Zinc Magnesium Aspartate (ZMA) Supplementation on Training Adaptations and Markers of Anabolism and Catabolism. J Int Soc Sports Nutr. 2004; 1(2): 12-20.