Most ZMA capsules are a combination of these two before-mentioned minerals and vitamin B6. Manufacturers claim taking it will promote lean muscle mass, improve sleep, and increase testosterone production. Let’s take a look at these an other claims made by the supplement makers.
One study took 42 experienced trainees and randomly divided the subjects into two groups. One group took ZMA and another took a placebo. They all lifted weights and were comparatively tested at the beginning of the trial, after one month (4 weeks), and again after two months (8 weeks). There was no difference in measurements between the two groups, leading researchers to this conclusion:
Results of the present study do not support contentions that ZMA supplementation increases zinc or magnesium status and/or affects training adaptations in experienced resistance trained males with normal zinc status. These findings are in contrast with the notion that ZMA supplementation can increase zinc and magnesium status, anabolic hormone status, and/or strength gains during training. These findings refute claims that ZMA supplementation in the amount and manner investigated provides ergogenic value to experienced resistance trained athletes. 1
So there’s the bottom line: there’s no reason to believe this supplement will help you get bigger or stronger. This in and of itself should you make you think twice about spending your money on it.
What about the claims of calcium interfering with the absorption of zinc? The few human studies I’ve seen indicated calcium supplementation might reduce zinc absorption by a few milligrams. One study noted that any issues with zinc absorption were offset by supplementing just 8 milligrams of zinc along with the calcium supplement.2
There are two other potential health problems you should consider before going overboard on zinc:
Copper Deficiency: Too much zinc could deplete the body’s stores of copper. Those who suffer from Wilson’s disease (which causes cooper to accumulate in the body) are often given zinc supplements to correct this condition. One study suggests that only 75 mg of zinc a day can quickly begin to deplete the body of copper. 3 Another study noted this problem in those using zinc–based denture creams. 4 Copper is essential for health, so artificially lowering the levels of this mineral is not advisable.
Prostate Cancer: Some studies have found correlations between zinc supplementation and prostate cancer (especially among those who supplemented for long time periods at high doses).5 But these studies have been criticized as “misleading” for flawed in research methods. The critics noted, for example, that other supplements (or toxins within the supplements) may account for the difference in cancer rates among subjects. They also pointed out that actual zinc levels were never tested, so we don’t know how much of the mineral was actually being absorbed by those who took the supplements.6
We might make a stronger case for the supplementation of magnesium:
. . . many people do not even get the RDA of 350 mg of magnesium daily. A therapeutic dosage could easily run between 400 mg and 1000 mg daily of elemental magnesium in divided doses. In people with normal kidneys, it is difficult to reach toxic levels of magnesium. However, too much oral magnesium will result in diarrhea. 7
You could add magnesium citrate to your daily supplementation if you are concerned about being deficient.
Vitamin B6 is probably responsible for the improved sleep some report with ZMA supplements. This water soluble vitamin play an important role in the production of certain neurotransmitters associated with sleep.
Putting it all together:
*There’s no evidence ZMA supplements make any difference in terms of size and strength.
*You could buy these minerals individually if you want to supplement them, but I’d recommend caution with zinc (especially if you are already taking supplements that have zinc, such as a multivitamin). I’d recommend keeping your total daily zinc supplementation to less than 30-40 milligrams (that’s what I normally do).
*Your best bet is to get these minerals through your diet. Foods like beef and liver, for example, are good sources of zinc. Supplements should only be seen as insurance against deficiencies.
1. J Int Soc Sports Nutr. 2 2004 Dec 31;1(2):12-20.), Effects of Zinc Magnesium Aspartate (ZMA) Supplementation on Training Adaptations and Markers of Anabolism and Catabolism.
2. Am J Clin Nutr. 1997 Jun;65(6):1803-9, High dietary calcium intakes reduce zinc absorption and balance in humans.
3. Am J Med Sci, 1993 Apr, 305(4):199-202, Treatment of Wilson’s disease with zinc XII: dose regimen requirements
4. Neurology. 2008 Aug 26;71(9):639-43, Denture cream: an unusual source of excess zinc, leading to hypocupremia and neurologic disease.
5. Cancer Causes Control. 2009 Jul;20(5):691-8. Epub 2008 Dec 18. Vitamin and mineral use and risk of prostate cancer: the case-control surveillance study.
6. Cancer Causes Control (2010) 21:1743–1744 DOI 10.1007/s10552-010-9595-5, Vitamin and mineral use and risk of prostate cancer: misleading?
7. Schachter, Michael B. (M.D., F.A.C.A.M.), The Importance of Magnesium to Human Nutrition