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Testosterone is the main sex hormone in men. It's best known for its role in the development of male sexual characteristics and physical features, but there are also many surprising and lesser known functions of testosterone that make it an important hormone in health and disease. Identifying whether someone has too much or too little testosterone can predict future diseases and even treat them. But knowing what is high, low or normal for an individual isn't straightforward.
Testosterone plays an important role in how male reproductive tissues such as the testicles and the prostate develop, as well as promoting what are known as secondary sexual characteristics, such as increased muscle, bigger bones, deep voice and the growth of body hair all the things we associate with being male. Females also produce testosterone, although in much lower amounts. It helps with the growth and maintenance of a woman's reproductive tissue, strengthens bones and can influence mood and behaviour.
As with many hormones, the importance of testosterone becomes even more apparent when we look ...