Magnesium and Testosterone: Get The Facts

What is Magnesium? Internet rumors suggest that magnesium is an impressive testosterone booster, especially for body-builders, but do research findings hold up to the hype? Studies show that supplementing with magnesium may not be all that effective aside from treating a magnesium deficiency.

Testosterone’s Effects on Muscle

We know from extensive research that testosterone is an anabolic hormone, namely, one that helps maintain muscle integrity instead of breaking it down. On a molecular level, testosterone activates satellite cells, which eventually turn into myoblast cells that generate muscle fibers. It also seems to inhibit fat synthesis. In studies on adult men who had low testosterone levels, subjects showed significantly reduced lean body mass compared to subjects with normal testosterone levels. For athletes who depend on muscle growth and maintenance, testosterone’s effects are highly coveted. However, long-term studies have shown that anabolic steroid use can lead to cardiovascular, reproductive, liver, and brain damage over time. 

Magnesium and Testosterone

Current marketing claims have tagged magnesium as a “natural” way of reaping the benefits of high testosterone without the concomitant risks of steroid abuse. While “natural” does not necessarily equate to “safe”, in this case, magnesium may not have significant effects on testosterone at all.

Molecular Interactions

Some research seems to show that magnesium may affect testosterone production and help free up testosterone so it can function. A study on rat testes found that moderate and high doses of magnesium enhanced the activity of two enzymes involved in making testosterone. Magnesium at high concentrations was also found to block testosterone from binding to SHBG (sex hormone binding globulin), a transport molecule that binds and inhibits testosterone’s functionality, thereby increasing free, bioavailable testosterone.

Magnesium’s Effects on Testosterone Levels

In terms of measureable increases in testosterone, supporting studies are few. So far, available studies show that if magnesium increases testosterone, it’s only minimally. An often-cited study on young athletes who took 10 mg/kg of magnesium sulfate 5 times a week for 4 weeks during training noted an increase in free testosterone after exhaustion compared to placebo. However, it’s unclear in the study whether the difference between the two groups could possibly be explained by a difference in testosterone levels at baseline. In a study on magnesium-deficient subjects, normalizing magnesium levels increased testosterone slightly, but the increase was not statistically significant.

Magnesium’s Effects on Athletic Performance

Research on whether magnesium’s minor effects on testosterone improve athletic performance is also limited and conflicting. One study shows that a supplement consisting of 30 mg of zinc monomethionine aspartate, 450 mg magnesium aspartate, and 10.5 mg vitamin B6 combined with intense physical activity increased testosterone levels compared to placebo. The subjects given the supplements also showed increased muscle strength compared to placebo. However, a similar supplement formulation was used in another study that failed to find any benefits on testosterone status or performance.

Some researchers seem to think that differences in study findings are due to unstandardized methods for measuring testosterone. Essentially, researchers don’t agree on what form of testosterone is the best indicator for overall testosterone activity.

Even if we remove testosterone from the equation, though, and just look at magnesium and athletic performance, research is still inconsistent. In a review of 12 different studies, 5 showed no positive effects of magnesium on performance, even with doses of up to 500 mg of magnesium per day for 3 weeks. A study of 24 young swimmers with what the researchers deemed were adequate magnesium levels showed no change in 100 m and 400 m freestyle times after 3 months of 486 mg of magnesium per day. In contrast, another study on swimmers suggested that there was a direct relationship between magnesium intake and 100 m freestyle times. To add to the confusion, those studies showing positive results tended to involve subjects who were magnesium-deficient, but this was not always the case.

Magnesium research suffers similar limitations to testosterone research. In the review of 12 studies, 6 did not account for initial magnesium status of the subjects before the studies began and the other 6 measured “total serum magnesium”. Magnesium is mostly stored inside our bones and soft tissue cells, so serum magnesium measurements may not be a reliable indicator of our total magnesium load. In some cases, studies did not measure initial magnesium status at all. This means that from these studies, we can’t know if magnesium is really adding any benefits or if magnesium supplementation is simply correcting a deficiency.

Magnesium Deficiency in Athletes

With all this talk about inconclusive research, we do know that magnesium deficiency is common in athletes and can affect muscle strength. In this sense, magnesium supplementation might be a good option for improving athletic performance in a significant number of athletes.

Surveys seem to show that magnesium intake in physically active individuals can be low. Established values for recommended magnesium intake include the daily RDA (recommended dietary allowance) – 350 mg for men and 280 mg for women – and DRI (dietary reference intake) – 400 mg for men and 310 mg for women. Young adults who engage in exercise have been found to have an average magnesium intake of 71% of the RDA. In a study on male and female collegiate athletes, magnesium intake was 70% of the DRI on average. One study found that athletes competing in sports requiring weight classifications found that magnesium consumption could be as low at 30% of the RDA.

On top of inadequate magnesium intake, exercise can affect serum magnesium levels. Intense and long-term exercise has been shown to reduce serum magnesium levels, leading to quicker fatigue and decreased endurance. Magnesium itself is required to sustain exercise and participates in mechanisms that lead to muscle contraction. Magnesium can be a limiting factor in athletic performance, and low levels can lead to inefficient oxygen use, muscle weakness, and spasms.

Magnesium supplementation in magnesium-deficient individuals can have profound effects on aerobic and anaerobic abilities. Just 25 days of 390 mg of magnesium per day was able to significantly improve oxygen uptake and work output in a study of magnesium-deficient male athletes. In collegiate athletes, magnesium supplementation was able to improve endurance performance. And young men taking more than 250 mg of magnesium per day during a 7-week strength-training program improved muscle strength and power. At a physiological level, magnesium supplementation can cause reductions in heart rate, ventilation, oxygen uptake, and carbon dioxide production during exercise, all factors indicative of increased work efficiency.

Note: 350 mg per day for adults is the established Tolerable Upper Intake Limit for magnesium supplements before adverse effects like nausea and vomiting begin. Very high doses can induce severe effects like difficulty breathing, low blood pressure, arrhythmias, and cardiac arrest.

The Bottom Line

Although research does not support the use of magnesium supplements to increase testosterone levels as a means of improving athletic performance, adequate magnesium levels are required for optimal muscle activity. Since magnesium deficiency is common and exercise tends to deplete the body of magnesium stores, athletes should consider investigating whether low magnesium levels are limiting their exercise results.

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