Testosterone (T) is the key androgen that both drives sexual development in men and underlies many vital physiological processes throughout the lifespan of the individual. Most of the testosterone in a man's body is produced in the testicles.
It plays an important role to:
Maintain reproductive tissues
Stimulate sperm production
Stimulate and maintain sexual function
Increase muscle mass and strength
Maintain bone strength
There is a numerical range of testosterone levels (300 - 1100ng/dL) that are considered normal in adult men.
Testosterone can fall below normal levels. This can happen when a signaling problem between the brain and the testes causes a drop in the amount of testosterone that is being produced. Another reason below normal testosterone levels can occur is when the body simply can't produce enough testosterone. When a man’s testosterone falls below a level of around 300ng/dL, it’s generally considered to be low.
It's natural for men to produce less testosterone as they age. What's not a natural part of aging is a medical condition known as male hypogonadism — which means there is less testosterone than normal. Symptoms include reduced sexual function, depressed mood, and decreased energy.
The NIH has defined male hypogonadism as a condition in which the testes do not secret hormones, such as testosterone, in the manner expected. Primary hypogonadism involves a malfunction of the testes themselves and may result from chromosome abnormalities (e.g. Klinefelter’s syndrome), local testicular surgery/disease, infection, mumps orchitis, radiation and renal failure. Central (or secondary) hypogonadism involves a defect in the pituitary or hypothalamus and may result from hypopituitarism, selective gonadotrophic deficiency, severe systemic illness or the patient being severely underweight. Additionally, healthy aging men experience a variety of hormonal changes, including decreasing serum testosterone levels.
Hypogonadism is often misdiagnosed as a host of other maladies, including depression and erectile dysfunction. It is conservatively estimated that adult male hypogonadism affects 19 million American men, up to 88% of who go untreated.
Current treatment guidelines focus on the restoration of the normal physiological testosterone level through the use of exogenous testosterone preparations.
The health consequences of low testosterone in adult men can be quite wide-ranging*:
Diminished sex drive
Loss of Energy
Increase in body fat
Men with low testosterone are also at increased risk of: