ZMA—a combination of zinc, magnesium, and vitamin B6—has been marketed for over twenty years as a “natural testosterone booster” and better sleep. The editors checked which studies this reputation is based on, what they actually found and for whom the supplement may make practical sense.
Where did the ZMA evidence base come from?
The history of ZMA as a sports supplement began with a small study by Brilla and Conte published in 2000 in the electronic Journal of Exercise Physiology Online. Participants were American college football players who received either a combination of zinc monomethionine/aspartate, magnesium aspartate, and vitamin B6, or a placebo during eight weeks of spring practice. The authors reported increases in free and total testosterone, as well as IGF-1 and strength gains in the ZMA group.
It was this work that became the basis of the supplement's marketing. However, critics immediately drew attention to an important detail: the ZMA formula was developed by a company related to one of the authors, and the research was funded by an interested party. A conflict of interest alone does not invalidate the results, but requires independent replication.
In addition, football players actively sweat during the season and often have an insufficient intake of trace elements. If part of the participants had a deficiency of zinc or magnesium, then the improvement of the hormonal profile could be a consequence of the elimination of the deficiency, and not a specific effect of the combination on a healthy person with a normal status.
Independent studies conducted subsequently had a different design and, importantly, controlled the diet of the participants. It is their results that today determine how ZMA is treated by the scientific societies of sports nutrition.
Testosterone and anabolic hormones
The most cited independent study is Wilborn et al. (2004), published in the Journal of the International Society of Sports Nutrition. Forty-two strength-trained men received either ZMA or a placebo for eight weeks. The researchers measured total and free testosterone, cortisol, IGF-1, as well as body composition and strength indicators. No significant differences between the groups were found for any of the hormonal markers.
In 2009, Koehler and colleagues investigated another question: whether high-dose zinc (as part of a ZMA-like supplement) alters testosterone levels and urinary excretion of steroid hormone metabolites. The work had an anti-doping origin — the authors wanted to find out whether the supplement distorts the athlete's steroid profile. The answer was negative: neither serum testosterone nor urinary metabolites changed significantly.
At the same time, there is a separate array of data on zinc as such. Prasad et al. (1996) showed that testosterone levels are reduced in zinc-deficient men and recover after correction of the status, and artificially induced deficiency lowers testosterone in healthy men. This is consistent with biology: zinc is needed for the work of many enzymes, including those involved in the synthesis of steroids and the function of the pituitary gland.
So the logic is this: zinc is necessary for normal hormonal function, and its deficiency can indeed lower testosterone. But additional zinc beyond the need for a person with a normal status does not "overdrive" hormones above the physiological level. It is this difference between deficit correction and normal stimulation that is key to understanding the entire evidence base for ZMA.
| Research | Participants | Duration | The main result |
|---|---|---|---|
| Brilla, Conte (2000) | Football students | 8 weeks | Increase in testosterone, IGF-1 and strength; financing by the manufacturer |
| Wilborn et al. (2004) | Trained men, strength training | 8 weeks | No differences from placebo in terms of hormones, body composition and strength |
| Koehler et al. (2009) | Healthy men | A short course of high-dose zinc | No changes in testosterone and urinary steroid metabolites |
| Prasad et al. (1996) | Adults with varying zinc status | Observation and intervention | Zinc deficiency reduces testosterone; correction restores |
Strength, endurance and body composition
In Brilla and Conte's work, the ZMA group showed better gains in quadriceps isokinetic strength than placebo. However, in a study by Wilborn et al., where strength was assessed by classical tests of maximal repetition of the bench press and leg press, as well as anaerobic power on a cycle ergometer, no effect of the supplement was found. The increase in strength in both groups was due to training.
In terms of body composition, the situation is similar: independent data show no additional increase in lean mass or reduction in fat mass from ZMA in people with adequate nutrition. The supplement has no mechanism that would allow us to expect such an effect in the absence of a deficiency.
There are practically no direct controlled studies of ZMA specifically for endurance performance. There is evidence for magnesium: reviews by Nielsen and Lukaski (2006) and Lukaski (2004) describe that magnesium deficiency impairs energy metabolism and increases oxygen demand during exercise, and correction of the deficiency improves performance. No convincing increase in performance has been demonstrated for people with normal magnesium levels.
Practical editorial conclusion: ZMA should not be considered as an ergogenic supplement in the classical sense, that is, as a means that directly increases strength or endurance. It is not in the same category as creatine, caffeine, or beta-alanine, which have a strong evidence base for a direct effect.
Sleep and recovery
The second popular promise of ZMA is deeper sleep and vivid dreams. Here, the evidence base is even weaker than for hormones. There are very few controlled studies of the combination of ZMA with an objective assessment of sleep (polysomnography or actigraphy) in athletes, and the conclusions are mostly based on data on individual components.
The most frequently cited work is Abbasi et al. (2012), in which older adults with primary insomnia received either magnesium or a placebo for eight weeks. Subjective sleep indicators, time to fall asleep, and some hormonal markers, including melatonin, improved in the magnesium group. However, these were elderly patients with insomnia, in whom the prevalence of suboptimal magnesium status is high, and extrapolation of these data to young athletes is incorrect.
Vitamin B6 in ZMA is involved in the synthesis of serotonin and, indirectly, melatonin. This explains the reports of users about more vivid dreams. However, the subjective feeling of "more vivid dreams" does not equal better recovery and is not a proven objective effect.
As for recovery markers — creatine kinase, muscle pain, inflammatory markers — the editors did not find separate qualitative studies of ZMA in athletes. Therefore, the claim of "accelerated recovery" should be considered as a hypothesis, not as an established fact.
Who ZMA can really help
The International Olympic Committee Consensus Statement on Nutritional Supplementation (Maughan et al., 2018) emphasizes that micronutrient supplementation is appropriate primarily when a deficiency is confirmed or there is a high likelihood of inadequate intake. An ISSN review (Kerksick et al., 2018) classifies ZMA as a supplement with limited or conflicting efficacy data.
Groups in which suboptimal zinc or magnesium status occurs more often include:
- athletes of weight-dependent sports on long-term diets with calorie restriction;
- vegetarians and vegans — due to the lower bioavailability of zinc from plant foods;
- athletes with intense sweating in a hot climate;
- people with the same type of diet, poor in nuts, whole grains, legumes, meat and seafood.
For these people, ZMA can be one of the convenient ways to close the need, although not the only and not necessarily the best one — it is often enough to adjust the diet or choose a separate magnesium or zinc preparation in a dose calculated for a specific situation.
For a person with a varied diet and normal micronutrient status, the supplement will most likely not have a noticeable effect on testosterone, strength, or body composition. If you are in doubt about your status, blood tests (serum zinc, magnesium), although limited, provide more information than a "random" test.
Editorial conclusion
The evidence base for ZMA is asymmetric: the only positive study on hormones and strength had no manufacturer funding, and independent studies have not replicated the effect. Zinc and magnesium are important for hormonal function and energy metabolism, but their effect is mainly manifested in the correction of deficiencies.
ZMA is not a testosterone booster in healthy individuals with a normal diet and should not be considered a substitute for a well-balanced diet, sleep and a well thought out exercise program.
If you do plan to take a supplement, evaluate the result soberly: a realistic expectation is the maintenance of the status of microelements, not an increase in strength indicators.
The editors recommend that you also read our articles "ZMA Side Effects", "How to Take ZMA: Dosage, Time of Administration, Duration" and "ZMA Myths".
References
- Brilla LR, Conte V. Effects of a novel zinc-magnesium formulation on hormones and strength. J Exerc Physiol Online. 2000;3(4):26â36.
- Wilborn CD, Kerksick CM, Campbell BI, 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):12â20.
- 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;63(1):65â70.
- Prasad AS, Mantzoros CS, Beck FW, Hess JW, Brewer GJ. Zinc status and serum testosterone levels of healthy adults. Nutrition. 1996;12(5):344â348.
- Abbasi B, Kimiagar M, Sadeghniiat K, et al. The effect of magnesium supplementation on primary insomnia in elderly: a double-blind placebo-controlled clinical trial. J Res Med Sci. 2012;17(12):1161â1169.
- Nielsen FH, Lukaski HC. Update on the relationship between magnesium and exercise. Magnes Res. 2006;19(3):180â189.
- Kerksick CM, Wilborn CD, Roberts MD, et al. ISSN exercise & sports nutrition review update: research & recommendations. J Int Soc Sports Nutr. 2018;15(1):38.
- Maughan RJ, Burke LM, Dvorak J, et al. IOC consensus statement: dietary supplements and the high-performance athlete. Br J Sports Med. 2018;52(7):439â455.
