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Results using GH Stak vary from individual to individual. Testimonial endorser’s results using it may be considered atypical. Testimonial endorsers have been remunerated by Muscle-Link. GH Stak is a trademark of Muscle-Link. These statements have not been evaluated by the U.S. Food and Drug Administration.
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www.ironmanmagazine.com \ MARCH 2008 49 little. Too much zinc leads to
an imbalance between zinc and copper, resulting in an ex- cess excretion of copper. The effects of a copper deficiency include a type of anemia and a decline in protective high-den- sity-lipoprotein cholesterol, and a serious copper deficiency could lead to a breakdown of the aorta, the large artery leading out of the heart, be- cause copper is required for the synthesis of collagen, which strengthens blood vessels.
While having sufficient zinc is vital for the func- tion of immune cells known as T cells—which, among other things, protect against viruses and tumor formation—getting too much zinc works in reverse, impeding immune reactions in the body. Taking as little as 80
milligrams of zinc daily will have an immune-suppressing effect in most people. It concentrates in the prostate gland, and one study found that con- sistently taking 100 milligrams of zinc or more daily led to a 290-percent in- crease in the risk of metastatic prostate cancer. Even taking only 53 milligrams of zinc daily can impair copper status in the body. Plus, while not having enough zinc impairs blood-platelet aggregation, which leads to increased bleeding time, having too much increases the risk of internal blood clotting, which is linked to heart attack and stroke.2
From an athlete’s point of view, zinc status can either help or hinder. Low zinc intake is associated with impaired muscle function, reduced strength and a greater propensity to fatigue pre- maturely during exercise. Among the enzymes activated by zinc is carbonic anhydrase, needed for the metabolism of carbon dioxide. So if you’re too low on zinc, the enzyme’s activity is impaired, which messes with your breathing and would result in premature exercise fatigue.3 Zinc also works with
various anabolic hormones, including testosterone, insulin, IGF-1 and growth
hormone. Without it, nitric oxide declines, which adversely affects hormone function and blood flow to exercising muscles. So can ZMA aid your bodybuild- ing efforts? If you know the effects of zinc deficiency, the benefits of a supplement like ZMA seem clear. Suppose, however, you get enough zinc in your diet—would ZMA still prove beneficial?
A recent study compared the effects of taking the suggested three-capsule dose of ZMA to those of taking a pla- cebo.4 The subjects were 14 healthy,
exercising young men whose baseline daily zinc intake averaged between 11.9 and 23.2 milligrams.
A study published in 2000 showed that semiprofessional athletes who took the suggested dose had a 30 percent increase in plasma testosterone and a corresponding increase in muscular strength compared to athletes not tak- ing the supplement. In the new study, however, those taking ZMA had no rise in testosterone or its urinary metabo- lites. The pills were analyzed and found to contain no trace of pro-hormones, although they did meet label specifi- cations. Other effects of ZMA in the subjects included a rise in urinary pH, or alkalinity, and a doubling of urinary flow over the eight-week study. The increased urine flow was likely related to the rapid excretion of zinc in the sub- jects taking ZMA.
While the authors noted that the training level of the subjects was infe- rior to that of the subjects in the 2000 study, both groups had similar zinc and testosterone measures before and after
the studies. The authors suggest that for those not deficient in zinc, taking ZMA won’t affect testosterone levels. They further suggest that the ZMA effect on pH, as well as the increased urinary flow, may prove a problem for some people, citing the 30-milligram dose, which is close to the suggested tolerable safe daily dose of 40 mil- ligrams. Since zinc is an ingredient in many other supplements bodybuilders use, such as meal replacements and vitamin-and-mineral capsules, that calls for caution on the part of supplement users. On the other hand, since stud- ies show that fish and chicken aren’t reliable sources of zinc, bodybuilders who eschew red meat may benefit from some type of zinc supplement.
Two other factors to consider are that only about 20 percent of a zinc supplement is absorbed under the best conditions (25 percent is absorbed from food). Other minerals, such as calcium and iron, speed zinc excretion. The other mineral in ZMA, magnesium, is also far more likely to be lacking in a typical bodybuilding diet. So a sup-
plement such as ZMA may prove useful for many people. Just don’t depend on it to raise your testosterone too. —Jerry Brainum
References
1 Ho, E. (2004). Zinc deficiency, DNA
damage and cancer risk. J Nutr Bio-
chem. 15:572-78.
2 Hughes, S., et al. (2006). The ef-
fect of zinc supplementation in humans on plasma lipids, antioxidant status and thrombogenesis.J Amer Coll Nutr. 25:4:285-91.
3 Lukaski, H. (2005). Low dietary zinc
decreases erythrocyte carbonic anhy- drase activities and impairs cardiorespi- ratory function in men during exercise.
Am J Clin Nutr. 81:1045-51.
4 Koehler, K, et al. (2007). Serum
testosterone and urinary excretion of steroid metabolites after administration of a high-dose zinc supplement. Eur J
Clin Nutr. 1-6: In press.
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