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The role of Magnesium and Zinc in Bodybuilding Supplements

Although there is a vast array of supplements targeted at the sporting community simply absurd in their claims, we are going to have a closer look at one product called ZMA, citing less grandiose claims, accompanied by plausible explanations, to see whether there is merit in such claims.

ZMA (30mg zinc monomethionine aspartate, 450mg magnesium aspartate and 10.5mg vitamin B6, which is added in order to improve absorption of zinc and magnesium) is mostly targeted at male athletes as a virility enhancer. It is said to boost their anabolic hormone levels, thus increasing strength, enabling faster recovery, improving sleep and generally wellbeing.

Zinc and magnesium are both known to be vital for human development and growth. These minerals are used by our bodies in more than 300 metabolic processes and they are the key component in the production of IGF-1, which is the active growth hormone metabolite.

Zinc is essential for development of sex hormones. Its deficiency is a common cause of low weight and childhood stunting, though this appears to be largely a third world problem. Zinc is highly concentrated in semen, being involved in sperm formation and motility. Infertile men typically have significantly lower levels of seminal zinc. Cellular concentrations of zinc happen to correlate with testosterone levels. Therefore, zinc depletion causes testosterone levels to fall. Zinc supplementation was found to almost double the testosterone levels in elderly gentlemen who suffered from marginal zinc deficiency. In addition, zinc also appears to inhibit the conversion of testosterone into oestrogens.

Magnesium possesses electrolyte actions and is needed for ensuring normal levels of calcium and potassium. Evidence shows that magnesium can prevent testosterone from binding to sex hormone binding globulin and thus increases the amount of available active testosterone. Magnesium is also vital for energy metabolism.

Zinc Magnesium Aspartate (ZMA) Trials

Data shows that American footballers who took ZMA at night-time had increased levels of total testosterone and free testosterone as well as IGF-I levels. Total and free testosterone levels were increased by an impressive 33% whereas they declined in those not supplemented. But, a later study in resistance trained athletes found no effect of ZMA on anabolic hormones. Why such a disparity?

There is a clear difference between the two studies. In the null-effect study, zinc and magnesium levels were already adequate and, therefore, supplementation had little impact on blood levels. In the positive study ZMA supplementation increased zinc levels by 30% but this was only to achieve levels similar to those found at baseline levels in the null-effect study.

Conclusion: zinc and magnesium are essential for growth and maintaining healthy anabolic hormone levels of testosterone and IGF-1. However, only physiological levels of zinc and magnesium are required. Basically, ZMA does not raise your hormone levels above normal levels but it helps restore them to the level they should be at if you were nutritionally replete.

How Much Do I Need?


The recommended daily allowance of zinc for males is 11-15mg, though it has been argued that optimal status requires higher levels of approximately 25mg/day. Surveys show that the average daily intake among men in the UK is only 10mg, being lowest in 19-24 years at 9mg. 34% of intake comes from meat, with red meat and seafood providing the best sources, and whereas plants can provide sufficient amounts alone, their phytates content may hinder absorption, placing vegans and vegetarians at high risk of zinc deficiency. Studies show that individuals undergoing strenuous exercise have increased zinc losses.


The recommended daily allowance for magnesium is approximately 400mg, yet the average man only ingests 310mg. As a matter of fact, 19-24 year olds were found to ingest only 260mg daily. The main sources of magnesium are cereals and grain products. Actually, 10-12% of a man’s average magnesium intake is attributable to beer intake. However, it is necessary to note here that alcohol depletes magnesium levels. It has also been suggested that individuals who undergo strenuous exercise need up to 20% more magnesium than the average population. In order to ensure that you are consuming enough magnesium from food, include green vegetables, whole grains and legumes in your diet. For instance, 100g of spinach provides 80mg of magnesium. 30g of cashews or almonds will provide the same amount (292mg and 268mg per 100g, respectively). Roasted potatoes with skin on provide 23mg per 100g, while baked beans contain around 43mg of magnesium per 100g.

Supplemental intakes of zinc and magnesium above the amount found in a ZMA supplement cannot be recommended. Consistently high zinc intakes can impede copper absorption and levels above 100mg/day are linked with an increased risk of prostate cancer. Excess amounts of magnesium can disrupt your mineral status and result in undesirable loss of calcium from the body.