Testosterone is a hormone that plays an important role in men's overall health. As men get older, their testosterone levels naturally fall. However, some men may experience low testosterone levels, also known as testosterone deficiency, which can lead to weaker bones, loss of muscle and changes in mood, like feeling depressed. About 30% of men between the ages of 40 and 79 are affected by low testosterone.
Low testosterone, or testosterone deficiency, happens when the testicles stop making testosterone or when testosterone levels in the body drop to low levels. There are two different types of low testosterone; one as a result of getting older or a problem with the testicles, and another as a result of disruption in the area of the brain responsible for the functioning of the testicles.