I heard that ejaculation greatly reduced your zinc stores.
That might be why some people benefit so much from ZMA

I believe the magnesium is what is the most potent there. It's very often lacking in modern diet, especially in anybody who take dairy products that contain a lot of calcium which is not balanced by magnesium. Notice that most food contain little calcium and a lot of magnesium. In fact, I believe that the calcium RDA is a scam that profits the dairy industries a lot. Sorry, out-topic here. But come on, a lot of people in the world doesn't not drink any dairy products and yet they don't suffer from bone problems.