2007 began with a breakthrough concerning the relation between bone marrow and semen production. In series of studies, stem cells were taken from a bone marrow and it was found that they may be able to become sperm cells not earlier than 3 to 5 years. This practically means that overly-active sexual activities will lead to weakened bones due to the specific nature of sperm production. Semen contains human growth hormone, testosterone, prostaglandins, alpha2-macroglobulin, insulin-like growth factor I, different amino acids, vitamins and minerals.