Definition: "An ergogenic aid is any substance or phenomenon that enhances performance "

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It really works - zinc is a testosterone booster

Zinc supplements raise testosterone production. Supplements manufacturers have been claiming this for years, but researchers as the Firat University in Turkey confirmed the claim a few years ago after doing animal and human studies. We read the articles and were convinced. Zinc works. But whether it's healthy to boost your testosterone level by taking zinc on the long term? We doubt it.

The researchers published their first results in Neuroendocrinology Letters in 2006. These came from an animal study in which they had given male rats daily injections of 3 mg zinc per kg bodyweight in the small intestine. The course of injections lasted for four weeks. At the end of the period the researchers got the animals to swim for thirty minutes.

A control group of rats also swam, but had not been given extra zinc. Yet another control group did nothing at all. The researchers then measured the rats' testosterone level immediately after completing the swimming test.

It really works - zinc is a testosterone booster

The physical activity led to a decrease of the testosterone level but not in the animals that had been given extra zinc. The lactic acid level of this group of rats also rose by less than that of the rats that swam but had not been given zinc. The researchers suspect that the body uses large amounts of zinc during physical exercise and that, as a result, other body processes that generate energy or produce hormones are hampered. Zinc is needed in these processes as well.

"Physiological doses of zinc supplementation may produce useful outcomes for performance", the researchers conclude. But rats aren't humans, so the researchers followed up with an experiment on human subjects: ten male students with an average age of 20 who had a sedentary lifestyle. The results of this study appeared a year after the animal study results. They were published in the same journal, by the way. [Neuro Endocrinol Lett. 2007 Oct;28(5):681-5.]

The students were given a daily dose of 3 mg zinc sulphate per kg bodyweight for a period of four weeks. That's a lot. If you weigh 80 kg you'd be getting get 240 mg zinc sulphate per day. That is approximately 50 mg of elemental zinc - 3.3 times the RDA.

After four weeks on the supplements, the students had to cycle to exhaustion point on an ergometer, pedalling harder as the test progressed. The researchers also got the students to perform the same test when they had not been stuffed full of zinc. The figure below shows the effect of the zinc supplement on the testosterone level.

It really works - zinc is a testosterone booster

The effect on free testosterone is particularly striking. At rest the level was fifty percent higher than normal, and this increased after the exhaustion test. In the control group the free testosterone level went down by about twenty percent after the cycling test.

The zinc supplement had a similar, but less marked, effect on the concentration of thyroxine. Levels of this hormone increased by about ten percent in the students that had taken zinc. The supplement did not prevent the concentrations of T3 and T4 from declining as a result of physical exertion. We know that athletes react differently to supplements and diets than non-athletes do. And the researchers have also done tests with athletes. More about these in the next posting.

Neuro Endocrinol Lett. 2006 Feb-Apr; 27(1-2):267-70.

Study: ZMA does not raise testosterone levels 07.04.2009