Low Testosterone

Testosterone is the most important sex hormone that men have. It is responsible for the typical male characteristics, such as facial, pubic, and body hair; muscle strength and mass; and a deep voice. Testosterone also helps maintain sex drive and sexual function, sperm production, red blood cell production, and bone health. The brain and pituitary gland (a small gland at the base of the brain) control the production of testosterone by the testes.

In adult men, low testosterone levels (also called hypogonadism) can cause a decrease in sex drive, poor erections, low sperm count, and enlarged breasts. Over time, low testosterone may cause a man to lose body hair, muscle mass, and strength and to gain body fat. Long-term low testosterone may also cause weak bones (osteoporosis), mood changes, decreased energy, and smaller testes.

A man's testosterone level normally decreases with age. Approximately 4 out of 10 men over the age of 45 have low testosterone levels.

Low testosterone can result from injuries, infections, medications, chronic diseases, or genetic conditions. Testosterone replacement therapy can improve symptoms of low testosterone.

Male hypogonadism means the testicles do not produce enough of the male sex hormone testosterone. There are 2 basic types of hypogonadism:

Primary. This type of hypogonadism — also known as primary testicular failure — originates from a problem in the testicles.

Secondary. This type of hypogonadism indicates a problem in the hypothalamus or the pituitary gland — parts of the brain that signal the testicles to produce testosterone.

Possible secondary causes of low testosterone include:

• Testicular injury or infection. Trauma or castration can cause the testes to produce lower than normal levels of testosterone.
• Inflammatory disease. Certain inflammatory diseases, such as sarcoidosis, histiocytosis, and tuberculosis, involve the hypothalamus and pituitary gland and can affect testosterone production, causing hypogonadism.
• HIV/AIDS. HIV/AIDS can cause low levels of testosterone by affecting the hypothalamus, the pituitary gland, and the testes.
• Chronic diseases. Diseases such as liver and kidney disease and type 2 diabetes can contribute to low levels of testosterone.
• Medications. The use of certain drugs, such as opiate pain medications and some hormones, can affect testosterone production.
• Obesity. Being significantly overweight at any age may be linked to hypogonadism.
• Normal aging. Older men generally have lower testosterone levels than younger men do. As men age, there's a slow and continuous decrease in testosterone production.
• Concurrent illness. The reproductive system can temporarily shut down due to the physical stress of an illness or surgery, as well as during significant emotional stress. This is a result of diminished signals from the hypothalamus and usually resolves with successful treatment of the underlying condition.

Both primary and secondary hypogonadism may be caused by an inherited (congenital) trait or something that happens later in life (acquired), such as an injury or an infection. At times, primary and secondary hypogonadism can occur together.

Risk factors for hypogonadism include:

• Kallmann syndrome
• undescended testicles as an infant
• mumps infection affecting your testicles
• injury to your testicles
• testicular or pituitary tumors
• HIV/AIDS
• Klinefelter syndrome
• hemochromatosis
• previous chemotherapy or radiation therapy
• untreated sleep apnea

Talk with your doctor if you have ongoing low sex drive, fatigue, erectile problems, or loss of muscle or bone mass. A simple blood test can check your testosterone level and guide treatment.