One of the best performance-enhancing supplements on the market might be one of the simplest. According to some studies, up to 70 percent of Americans are deficient in magnesium. That is bad news for gym-rats, because recent research indicates that magnesium levels seem to mirror testosterone levels.
A study published in the International Journal of Andrology found a positive relationship between magnesium and anabolic hormones, namely testosterone and IGF-1. Scientists suspect that the magnesium blunts certain inflammatory processes that inhibit production of these hormones.
Look for supplements containing magnesium citrate, which is better absorbed than the more common magnesium oxide.