Causes
The decrease in testosterone is an important factor in men suspected of having andropause. However, as men age, not only does the body start making less testosterone, but also the levels of another hormone, called sex binding hormone globulin (SHBG), which pulls usable testosterone from the blood, begins to increase. SHBG binds some of the available testosterone circulating in the blood. The testosterone that is not bound to the SHBG hormone is called bioavailable testosterone, meaning it is available for use by the body.
Men who experience symptoms associated with andropause have lowered amounts of bioavailable testosterone in their blood. Therefore, tissues in the body that are stimulated by testosterone receive a lower amount of it, which may cause various physical and possibly mental changes in a person such as mood swings or fatigue.