Testosterone is a male hormone mostly produced in the testicles. Other hormones produced in the brain are in part responsible for “telling” the testicles to produce testosterone. When there is a deficiency of testosterone circulating in the blood (which can be determined by a blood test to measure the testosterone level), this can be associated with a loss of libido (sexual desire) and erectile dysfunction. Causes of a low testosterone include a problem with a certain part of the brain (pituitary gland) or inadequate production of testosterone by the testicle, (which may be suggested by the finding of atrophic (small) testicles on physical examination. A rare cause of low testosterone levels is a pituitary tumor. However, it should be stressed that this is a rare cause of erectile dysfunction. One option for the treatment of erectile dysfunction due to low testosterone levels is testosterone supplementation.
Causes include diabetes, spinal cord injury, and other neurologic disorders. Radical prostatectomy impotence is not uncommon, and prostate radiation side effects also include erectile dysfunction. The nerves related to erectile function course along the area of the prostate and can be damaged during radical prostatectomy or by prostate radiation.
A very common cause of erectile dysfunction is vascular disease, and ED can be a symptom of heart disease.