In both men and women, testosterone levels peak between 25 to 30 years of age and thereafter drop approximately 1-2% annually. At the age of 60, testosterone levels are typically only 40-50% of youthful levels and may be lower due to stress and related lifestyle issues such as diet, exercise, and sleep patterns. This lowering in testosterone has been linked to a poorer health outcome in many areas of life.
LOW TESTOSTERONE AS MEN AGE
Male hypogonadism/low testosterone (HG) is a clinical entity due to any condition impairing testis action, i.e. the production of sex steroids (androgens) and spermatozoa. HG can be either congenital or acquired (such as severe stress) and it can be related to any alteration in the central control of testicular function (central, secondary or hypogonadotropic HG) or to primary damage to the testis itself (primary or hypergonadotropic HG).
In addition, an HG-like syndrome can also be due to any impairment in androgen activity, for example through increased levels of sex hormone binding globulin (SHBG), a protein that binds tightly to testosterone (T), thereby limiting its biological effects. The classification of HG according to the site of the impairment is clinically useful because it helps to determine how it is best addressed. HG can also be a result of the normal aging process or poor nutrition and prolonged low testosterone has been associated with poor overall health.
TESTOSTERONE AND SEXUAL FUNCTION
In men, Testosterone can be considered to drive sexual behavior because it enhances several key steps of the entire male sexual response. Based on this assumption, finding a deterioration of sexual function in men with HG would not be surprising.
TESTOSTERONE AND ERECTILE DYSFUNCTION
Penile erection relies on the integrity and functioning of the vasculature of the corpora cavernosa. T has an important role in regulating penile integrity and functioning. It is known that T is involved in the development of the human penis during fetal life and in its growth during the first months of life (mini-puberty) as well as during puberty. Testosterone is also required for a healthy erection and a libido to match it.
LIBIDO AND TESTOSTERONE
Sexual desire is the motivational state that may prompt individuals to seek out and engage in sexual activity. Cognitive, sensory and emotional stimuli perceived as sexually meaningful can stimulate the brain and arouse sexual desire, which is the first step of the entire sexual response in both males and females. The brain area involved in the processing of sexual stimuli responsible for sexual desire is the mediobasal hypothalamus and limbic system, where the androgen receptor (AR) is expressed. Data from animal models suggest that T plays an important role in libido in men and women.
THE TAKE-HOME MESSAGE SURROUNDING TESTOSTERONE
Testosterone is deeply involved in the physiology of the entire male sexual response. Sexual dysfunctions represent the most specific of the putative clinical features of hypogonadism and, according to research, they allow the diagnosis of hypogonadism to be made in men with low Testosterone. However, a wide range of factors other than low Testosterone can disrupt sexual response at one or more levels, thus resulting in sexual dysfunction, including ED, low sexual desire and ejaculatory disorders.