Dr. Lee was born in Shanghai, China, and received his college and medical training in the United States. He is fluent in English and three Chinese dialects. He graduated with chemistry departmental honors from Harvey Mudd College. He was appointed president of AOA society at UCLA School of Medicine. He underwent internal medicine residency and gastroenterology fellowship training at Cedars Sinai Medical Center.
Dr. Nabili received his undergraduate degree from the University of California, San Diego (UCSD), majoring in chemistry and biochemistry. He then completed his graduate degree at the University of California, Los Angeles (UCLA). His graduate training included a specialized fellowship in public health where his research focused on environmental health and health-care delivery and management.
Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.
Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
The ability to achieve and sustain erections requires
a healthy nervous system that conducts nerve impulses
in the brain, spinal column, and penis,
healthy arteries in and near the corpora cavernosa,
healthy smooth muscles and fibrous tissues within the corpora cavernosa,
adequate levels of nitric oxide in the penis.
Erectile dysfunction can occur if one or more of these requirements are not
met. The following are causes of erectile dysfunction:
Aging: There are two reasons why older men are more likely to experience
erectile dysfunction than younger men. First, older men are more likely to
develop diseases (such as heart attacks, angina, cardiovascular disease, strokes, diabetes mellitus, and
high blood pressure) that are associated with erectile dysfunction. Second, the
aging process alone can cause erectile dysfunction in some men, primarily by
decreasing the compliance of the tissues in the corpora cavernosa, although it
has been suggested, but not proven, that there is also decreased production of
nitric oxide in the nerves that innervate the corporal smooth muscle within the
Diabetes mellitus: Erectile dysfunction tends to develop 10-15 years
earlier in diabetic men than among nondiabetic men. In a population study of men
with type I diabetes for more than 10 years, erectile dysfunction was reported
by 55% of men 50-60 years of age. The increased risk of erectile
dysfunction among men with diabetes mellitus may be due to the earlier onset and
greater severity of atherosclerosis that narrows the arteries and thereby
reduces the delivery of blood to the penis. When insufficient blood is delivered
to the penis, it is not possible to achieve an erection.
Diabetes mellitus also
causes erectile dysfunction by damaging both sensory and autonomic nerves, a
condition called diabetic neuropathy. Smoking cigarettes, obesity, poor control
of blood glucose levels, and having diabetes mellitus for a long time further
increase the risk of erectile dysfunction in diabetes. In addition to atherosclerosis
and/or neuropathy causing ED in diabetes, many men with diabetes also develop a myopathy
(muscle disease) as their cause of ED in which the compliance of the muscles in
the corpora cavernosa is decreased, and clinically this presents as an inability
to maintain the erection.
Hypertension (high blood pressure): People with essential hypertension or arteriosclerosis have an increased risk of developing erectile dysfunction. Essential hypertension is the most common form of hypertension; it is called essential hypertension because it is not caused by another disease (for example, by kidney disease). It is not clearly known how essential hypertension causes erectile dysfunction; however, those with essential hypertension have been found to have low production of nitric oxide by the arteries of the body, including the arteries in the penis. High blood pressure also accelerates the progression of atherosclerosis, which in turn can contribute to erectile dysfunction. Scientists now suspect that the decreased levels of nitric oxide in patients with essential hypertension may contribute to erectile dysfunction.
Cardiovascular diseases: The most common cause of cardiovascular
diseases in the United States is atherosclerosis, the narrowing and
hardening of arteries that reduces blood flow. Atherosclerosis typically
affects arteries throughout the body and is aggravated by hypertension, high
blood cholesterol levels, cigarette smoking, and diabetes mellitus. When
coronary arteries (arteries that supply blood to the heart muscle) are
narrowed by atherosclerosis, heart attacks and angina occur. When cerebral
arteries (arteries that supply blood to the brain) are narrowed by
atherosclerosis, strokes occur. Similarly, when arteries to the penis and
the pelvic organs are narrowed by atherosclerosis, insufficient blood is
delivered to the penis to achieve an erection. There is a close correlation
between the severity of atherosclerosis in the coronary arteries and
erectile dysfunction. For example, men with more severe coronary artery
atherosclerosis also tend to have more erectile dysfunction than men with
mild or no coronary artery atherosclerosis. Some doctors suggest that men
with new onset erectile dysfunction should be evaluated for silent coronary
artery diseases (advanced coronary artery atherosclerosis that has not yet
caused angina or heart attacks).
Cigarette smoking: Cigarette smoking aggravates atherosclerosis and
thereby increases the risk for erectile dysfunction.
Nerve or spinal cord damage: Damage to the spinal cord and nerves in the pelvis can cause erectile dysfunction. Nerve damage can be due to disease, trauma, or surgical procedures. Examples include injury to the spinal cord from automobile accidents, injury to the pelvic nerves from prostate surgery for prostate cancer (prostatectomy), radiation to the prostate, surgery for benign prostatic enlargement,
multiple sclerosis (a neurological disease with the potential to cause
widespread damage to nerves), and long-term diabetes mellitus.
Substance abuse: Marijuana, heroin, cocaine, methamphetamines, crystal meth, and alcohol abuse contribute to erectile dysfunction. Alcoholism, in addition to causing nerve damage, can lead to atrophy (shrinking) of the testicles and lower testosterone levels.
Low testosterone levels: Testosterone (the primary sex hormone in men) is
not only necessary for sex drive (libido) but also is necessary to maintain
nitric oxide levels in the penis. Therefore, men with hypogonadism (diminished
function of the testes resulting in low testosterone production) can have low
sex drive and erectile dysfunction.
Depression and anxiety: Psychological factors may be responsible for
erectile dysfunction. These factors include stress, anxiety, guilt, depression, widower syndrome, low self-esteem, posttraumatic
stress disorder, and fear of sexual failure (performance anxiety). It is
also worth noting that many medications used for treatment of depression and
other psychiatric disorders may cause erectile dysfunction or ejaculatory