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From The May 2001 Issue of Nutrition Science News
ZMA: Is This Prohormone Alternative Worth it?
Edmund R. Burke, Ph.D.
Many strength and power athletes are taking notice of a supplement called ZMA, a patented, trademarked product sold as a natural alternative to prohormones such as androstenedione and androstenediol. These prohormones, used to add lean body mass and increase strength, are banned by many sports organizations.
ZMA combines zinc monomethionine aspartate (30 mg), magnesium aspartate (450 mg), and vitamin B6 (10.5 mg) in a formula designed to enhance muscle strength, endurance, healing, and recovery. To date, however, only one published abstract supports these claims. Furthermore, published studies suggest that magnesium alone may generate similar results as those claimed by this product.
Essential Zinc and Magnesium
Zinc is an anabolic mineral required for production of growth hormone and testosterone, which promote tissue repair, healing, and muscle growth. Magnesium helps transport oxygen to muscle tissue, thereby promoting strength, endurance, and relaxation. Magnesium also activates enzymes necessary for metabolism of carbohydrates and amino acids. In vitro, vitamin B6 potentiates zinc's inhibitory effect on the enzyme 5A-reductase, which converts testoerone to dihydrotesterone. This conversion interferes with testosterone's anabolic effects in the body, so the combined supplements keep testosterone around longer.1
Researchers have examined the effects of zinc supplementation on muscle strength and endurance using isometric and isokinetic tests in the knee extensor and flexor muscle groups. In a 14-day, double-blind, placebo-controlled study of 16 female volunteers, 135 mg/day zinc significantly increased muscle strength and endurance compared to placebo.2 However, this is an enormous and potentially unsafe dose of zinc, although no adverse effects were reported.
Magnesium is essential for energy production by both aerobic and anaerobic metabolism, as well as muscle-protein formation and regulation. A magnesium deficiency can cause muscle weakness and cramps. Magnesium supplementation, on the other hand, also has been shown to increase muscle strength.
In a 1992 double-blind, placebo-controlled study in the exercise and sport science laboratory at Western Washington University in Bellingham, researchers first analyzed three-day diet records of 26 college students and then calculated their magnesium intake. One group of 12 supplemented with magnesium oxide to bring their magnesium intake, including diet, to 8 mg/kg body weight/day. The remainder received placebo. During the seven-week trial, subjects participated in a strength-training program. Results showed that the supplemented group significantly increased peak quadriceps torque, measured by leg presses, by 26 percent compared to 10 percent for the placebo group.3 Furthermore, German researchers have found that 300 mg/day magnesium enhances sleep efficiency, at least in those older than 50.4
These results indicate that even simple magnesium oxide can be absorbed and produce a positive effect. The results suggest that this form of magnesium could perform just as well as ZMA.
Why ZMA?
ZMA—as well as zinc alone—has been shown to increase anabolic hormone levels, including free testosterone and IGF-1 (insulinlike growth factor), hormones that may be suppressed in hard-training athletes.
The ZMA study most often cited as evidence of efficacy was co-investigated by Lorrie Brilla, Ph.D., at Western Washington University, and Victor Conte of Balco Labs in Burlingame, Calif. Conte is the inventor and patent owner of ZMA. Brilla and Conte studied 12 NCAA division II football players who took ZMA nightly during an eight-week spring training program. A separate group of 15 took placebo.
In the athletes taking ZMA, researchers measured a 30-percent increase in both free and total testosterone. (Free testosterone exists in blood; total includes levels in blood and in cells.) Testosterone levels in the placebo group declined by 10 percent, a result of hard training. The placebo group displayed a 21.5 percent decline in blood IGF-1 levels, while there was no significant change in the ZMA group.
In addition to improvements reported in anabolic hormone levels and sleep quality, the athletes made significantly greater gains in muscle strength and power. After eight weeks of training, the ZMA group experienced an 11.6 percent increase, compared to a 4.6 percent increase in the placebo group.5
The muscle-strength increase may have been mediated by the anabolic hormone increases in the ZMA group, or could have been mediated by the magnesium- improving muscle energetics, neural signaling, or both.6
Ultimately, the anabolic hormone increases are not important to athletes if they do not get more muscular. There were no changes in body weight in either the ZMA or placebo groups, suggesting that ZMA has no effect on muscle mass. However, there was a notable increase in strength and power. Thus, the observed increases with ZMA are no more striking than the increases observed with magnesium oxide. Clearly, more research is needed before trumpeting the effectiveness of ZMA.
Exercise Caution
Because calcium interferes with zinc and magnesium absorption, no ZMA, zinc, or magnesium supplements should be taken with dairy products or other calcium-containing foods or supplements. In addition, it is important to avoid high doses of zinc; several studies indicate that 50 mg zinc or more per day may reduce levels of copper, HDL (good) cholesterol, and even the antioxidant enzyme superoxide dismutase (SOD) in as few as 14 days. Magnesium has a low order of toxicity, although excessive intake may lead to diarrhea.
The results of the limited, preliminary research on ZMA offers evidence that magnesium supplementation may help healthy young men enhance their athletic performance. The research linking zinc to performance is tenuous. Zinc depletion appears to reduce muscle endurance (but not peak strength/force), and unsafe doses of zinc after depletion do not reinvigorate lost muscle endurance despite correcting blood-zinc concentrations.7
ZMA is marketed as a natural testosterone-boosting supplement for athletes, an alternative to androstenedione. Because ZMA is not a prohormone or hormone precursor, it does not adversely affect blood hormone levels. Certainly ZMA costs less than androstenedione, but whether it is more beneficial than magnesium is still uncertain.
Sidebars:
Zinc and Magnesium Deficiency Problems
Edmund R. Burke, Ph.D., is an exercise physiologist at the University of Colorado, Colorado Springs.
References
1. Stamatiadis D, et al. Inhibition of 5 alpha-reductase activity in human skin by zinc and azelaic acid. Br J Dermatol 1988 Nov;119(5):627-32.
2. Krotkiewski M, et al. Zinc and muscle strength and endurance. Acta PhysiIogica Scand 1982;116:309-11.
3. Brilla LR, et al. Effect of magnesium supplementation on strength training in humans. J Am Coll Nutr 1992;11(3):326-9.
4. Hornyak M, et al. Magnesium therapy for periodic leg movements-related insomnia and restless legs syndrome: an open pilot study. Sleep 1998;21(5):501-5.
5. Montgomery I, et al. Physical exercise and sleep: the effect of the age and sex of the subjects and type of exercise. Acta PhysiIogica Scand Suppl 1988;574:36-40.
6. Brilla LR, Conte V. A novel zinc and magnesium formulation (ZMA) increases anabolic hormones and strength in athletes. Sports Med Train Rehab. (In Press) Abstract presented Nov. 14, 1998, at the Annual Meeting of the Southwest Chapter of the American College of Sports Medicine.
7. Brilla LR, Conte V. Effects of zinc-magnesium formulation increases anabolic hormones and strength in athletes. Med Sci Sports Exer 1999;31(5):483.
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