• Testosterone levels are not always at a constant level for men. Many different factors can cause testosterone levels to decline. Declining levels of testosterone may cause erectile dysfunction, infertility, sexual dysfunction, lowered bone density, and muscle loss.


    According to the Mayo Clinic, it is natural for testosterone levels to slowly diminish as men age. The American Association of Clinical Endocrinologists reports that up to 30 percent of men aged 75 and older have lower than normal levels of testosterone.

    Injuries and Illness

    A man who has severely injured his testes can suffer from a decrease of testosterone production. Treating cancer with radiation and/or chemotherapy can adversely affect testosterone production. Contracting mumps which infiltrate the salivary glands and the testes can also decrease testosterone production.

    Pituitary disorders

    A tumor on or near the pituitary can cause a disruption of normal testosterone production. Radiation treatment on the brain, in the vicinity of the pituitary, can also adversely affect normal testosterone production.


    According to The Journal of Clinical Endocrinology and Metabolism, February 2007, poor health and obesity increases the rate of testosterone decline in aging men.

    Endurance Training

    According to the Encyclopedia of Sports Medicine and Science, men who practice endurance training, such as long-distance running, have lowered testosterone levels while they are at rest. The mechanisms responsible for lower levels of the hormone are unclear.


    Journal of Andropause Testosterone Deficiency

    Encyclopedia of Sports Medicine and Science: Testosterone and Reproductive Dysfunction

    More Information: Male Hypogonadism

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