Victor Conte, of BALCO Laboratories, is probably more known for his legal troubles than for his development of a commonly known neutraceutical called ZMA® (zinc magnesium aspartate). ZMA® has been popularized since 1999 by advertisements that purport its benefits in testosterone enhancement and muscle building potential. In this scientific review, ZMA® is stripped of its influential advertisements and put under the microscope.
What exactly is ZMA®?
ZMA® is simply a registered trademark name of SNAC system, Inc. which consists of a vitamin and mineral blend containing1:
- Zinc (as monomethionine and aspartate): 15-30 mg/dose
- Magnesium (as aspartate): 200-450 mg/dose
- Vitamin B6: 10.5 mg/dose
Zinc is a nutrient people need to stay healthy. The body needs zinc to grow and develop properly. Zinc also helps wounds heal and helps the body’s immune system work correctly. Finally, people need zinc to be able to taste and smell properly. Getting too much zinc causes nausea, vomiting, loss of appetite, stomach cramps, diarrhea, and headaches. If you take too much zinc for a long time, it can cause problems such as low copper levels, low immunity, and low levels of HDL cholesterol (the “good” cholesterol). The safe upper limits for zinc in adults aged 19 and older is 40 mg.2
Magnesium is the fourth most abundant mineral in the body and needed for more than 300 biochemical reactions. It helps maintain normal muscle and nerve function, keeps heart rhythm steady, supports a healthy immune system, and keeps bones strong. Magnesium also helps regulate blood sugar levels, promotes normal blood pressure, and is known to be involved in energy metabolism and protein synthesis. There is an increased interest in the role of magnesium in preventing and managing disorders such as hypertension, cardiovascular disease, and diabetes. The tolerable upper intake levels for magnesium in adults aged 19 and older is 350 mg.3
Vitamin B6 is a water-soluble vitamin that exists in three major chemical forms: pyridoxine, pyridoxal, and pyridoxamine. It performs a wide variety of functions in your body and is essential for your good health. For example, vitamin B6 is needed for more than 100 enzymes involved in protein metabolism. It is also essential for red blood cell metabolism. The nervous and immune systems need vitamin B6 to function efficiently, and it is also needed for the conversion of tryptophan (an amino acid) to niacin (a vitamin). Too much vitamin B6 can result in nerve damage to the arms and legs. This neuropathy is usually related to high intake of vitamin B6 from supplements, and is reversible when supplementation is stopped. The Food and Nutrition Board of the Institute of Medicine has established an upper tolerable intake level (UL) for vitamin B6 of 100 mg per day for all adults.4
What is ZMA® claimed to do?
According to information provided on SNAC System, Inc.’s website, this is how their ZMA® product is described:5
Figure 1: Edited snapshot of ZMA® description on SNAC System, Inc.’s product website page.5 Content that did not directly address the ZMA® product has been blurred.
First, I’m going to clarify something involving a late 90’s research study involving ZMA® usage with members of a University football team (as referenced in the snapshot above). Companies typically use the outcome of this research study when marketing ZMA®. I will confirm that Victor Conte, of BALCO Laboratories, was one of the researchers stated in that study. Conte’s financial interest in the ZMA® study and SNAC System, Inc.‘s financial support of the research is suspect from a legitimacy standpoint.6 Also PubMed, a peer-reviewed research hub, didn’t accept that particular ZMA® study from Brilla and Conte. So without further ado, let’s dive into the real research surrounding ZMA®.
What does the latest peer-reviewed research tell us about ZMA®?
In a study published in the Journal of the International Society of Sports Nutrition (2004), a commercial supplement containing zinc magnesium aspartate (ZMA®) was put to the test. During the 8-week double blind study, forty-two resistance trained males were randomly assigned to either a dextrose placebo (non-active) or ZMA® supplement which they consumed 30-60 minutes prior to bedtime. Subjects were tested at the 0, 4, and 8 week session for body composition assessment, 1-rep maximum and muscular endurance for the bench and leg press, Wingate anaerobic power, and anabolic/catabolic blood analysis along with other health markers.7
The results of this study concluded that while there was a slight 12-17% increase in serum zinc levels, ZMA® supplementation had no significant effects on total/free testosterone, IGF-1, growth hormone, cortisol, the ratio of cortisol to testosterone, or muscle and liver enzymes in response to training. In addition, no significant effects were observed between the placebo (non-active) and ZMA® supplement groups in measurements of 1-rep maximum strength, upper or lower body muscle endurance, or anaerobic sprint capacity.7
Another analysis of the “significantly increase anabolic hormone production” ZMA® claim
In a study published in the European Journal of Clinical Nutrition (2009), researchers narrowed their focus to find a direct relationship between ZMA® supplementation and serum testosterone. During the 8-week trial, fourteen resistance trained males aged 22-33 years were assigned either three capsules per day of ZMA® or three capsules per day of D-lactose monohydrate (as a visually indistinguishable placebo) in a placebo-controlled, double-blind manner. Prior to the trial, the zinc intake levels of all the subjects ranged between 11.9 and 23.2 mg day, which affirmed that the subjects were not zinc deficient.8
Blood and urine samples were collected before the start of supplementation and taken weekly within and at the end of the 8-week trial. Samples were collected in the morning between 0900 and 1100 hours as subjects reported to the laboratory at the same time of day every week.8
The results of this study again concluded that while serum zinc was raised in the ZMA® group, there were no significant changes in serum testosterone. Also, urine markers of testosterone and its metabolism were not altered by the use of ZMA®.8
While serum zinc levels were higher in the ZMA® group, so was the urinary zinc excretion which indicated proper zinc balancing in the body. This is important to note because it appears that in cases of zinc deficiency, testosterone may be negatively lower but can be normalized when sufficient zinc is provided in the regular diet. However, to much zinc in the diet will simply be excreted and therefore cannot further increase serum testosterone.8
Conclusion
While research does indicate that zinc intake can increase testosterone in those consuming a zinc deficient diet, it has no significant impact on those who are consuming a zinc sufficient diet as established by the Recommended Dietary Allowances (RDAs) for Zinc:
Figure 2: Recommended Dietary Allowances (RDAs) for Zinc.2
The argument to purchase ZMA® as a sports supplement to aid in muscle strength, endurance, healing and tissue repair seems to be outweighed by the most recent clinical trial outcomes. This decision is clearly up to the end user, but it’s a perfect example of how advertisements and true science can conflict significantly.
ZMA® is a registered trademark of SNAC System, Inc. Corporation California.
References
1 SNAC Scientific Nutrition for Advanced Conditioning. http://www.snac.com. Accessed on 06/21/2010.
2 Office of Dietary Supplements National Institutes of Health. http://ods.od.nih.gov/factsheets/Zinc-QuickFacts.asp. Accessed on 06/21/2010.
3 Office of Dietary Supplements National Institutes of Health. http://ods.od.nih.gov/factsheets/magnesium.asp. Accessed on 06/21/2010.
4 Office of Dietary Supplements National Institutes of Health. http://ods.od.nih.gov/factsheets/vitaminb6.asp. Accessed on 06/21/2010.
5 SNAC Scientific Nutrition for Advanced Conditioning. http://www.snac.com/products.htm. Accessed on 06/21/2010.
6 L. R. Brilla, Western Washington University, Bellingham, WA 98225, and V. Conte, BALCO Laboratories, Burlingame, CA 94010. A Novel Zinc and Magnesium Formulation (ZMA®) Increases Anabolic Hormones and Strength in Athletes. Sports Medicine, Training and Rehabilitation Journal, November 1998 (in press).
7 Wilborn CD, Kerksick CM, Campbell BI, Taylor LW, Marcello BM, Rasmussen CJ, Greenwood MC, Almada A, Kreider RB. Effects of Zinc Magnesium Aspartate (ZMA®) Supplementation on Training Adaptations and Markers of Anabolism and Catabolism. J Int Soc Sports Nutr. 2004 Dec 31;1(2):12-20.
8 Koehler K, Parr MK, Geyer H, Mester J, Schänzer W. Serum testosterone and urinary excretion of steroid hormone metabolites after administration of a high-dose zinc supplement. Eur J Clin Nutr. 2009 Jan;63(1):65-70.