In the early years of my cardiology practice, I was surprised by the number of men with heart disease who also suffered from impotence. In fact, being incapable of having an erection was the norm rather than the exception after heart attack. In those days, impotence was widely attributed to the psychological depression that often followed heart attack.
But closer questioning often revealed a very different story—men would admit that struggles to achieve an erection usually preceded a heart attack or other cardiac event by one, two, or three years. Back then, the pattern of erectile dysfunction and cardiac disease was so widespread, that most in the medical profession attributed it to simple “aging,” as common as wrinkles and constipation.
Today, we know that a convergence of findings relates male impotence—called erectile dysfunction (ED)—with heart disease. The two conditions are varied expressions of a common phenomenon, and are surprisingly similar. If you have one, you’re likely to have the other.
Powerful clinical and scientific experience suggests a close link between erectile dysfunction and heart disease. Studies like the Health Professionals Follow-up Study have revealed the risk factors for erectile dysfunction to be very similar to those for heart disease. Hypertension, smoking, diabetes, high cholesterol, obesity, and physical inactivity all strongly predict sexual dysfunction in men, as they do heart disease.1
The Massachusetts Male Aging Study of 1,290 men, aged 40–70 years, has documented the extraordinarily high prevalence of erectile dysfunction among aging men: 50% of men at 50 years of age, and 70% by age 70 have erectile dysfunction.2 Furthermore, a recent Italian study of men with severe heart disease has uncovered an astounding 93% with erectile dysfunction 24 months before their heart attack or onset of heart disease symptoms.3
As many of us failed to recognize years earlier, these studies reveal that erectile dysfunction and coronary disease are, in many respects, one and the same. The risks are identical, the paths to both are largely the same, though the immediate consequences are different.
In their younger years, most men take the physical act of attaining an erection for granted, as natural and automatic as sweating or digestion. But a complex interplay of physio-logical activities needs to be initiated and precisely coordinated to trigger, achieve, and maintain an erection.
First of all, libido (sexual desire) triggers a sympathetic (adrenaline-dependent) nervous system reaction mediated through the thoracic spinal cord. Also important is tactile stimulation, the pleasurable effect of touch, which is mediated through the acetylcholine-dependent parasympathetic nervous system. Both the sympathetic and parasympathetic forces regulate the release of nitric oxide—the universal artery-relaxing agent—from the cells lining the penile arteries and all its smaller branches. Nitric oxide causes the arteries to enlarge, increasing blood flow into the penile tissues. This is followed by compression of blood-draining penile veins, which causes blood to engorge the penis and create an erection.4
A disruption anywhere along the complex chain of events will impair the capacity to have an erection. Any man who has experienced the frustration of male impotence knows that the consequences extend beyond physical dissatisfaction to anxiety, tension, and embarrassment. A common reason for failure of the erectile apparatus is disruption of the path leading to nitric oxide production and blood flow control.
Nitric Oxide—A Common Denominator
Nitric oxide is crucial for a normal erection to proceed. A universal substance in biological systems, nitric oxide has a primal, powerful ability to dilate (relax) blood vessels.5-7 In the human body, nitric oxide exerts its dilating effects for only a few moments before being degraded.
In the vessels that supply the heart, healthy arteries enlarge in diameter up to 50% during exercise when sufficient nitric oxide is present. Because of its brief half-life, a continual supply of nitric oxide is required for optimal effect. If the supply of nitric oxide is inadequate, endothelial dysfunction—a core factor in heart disease—is made worse. Endothelial dysfunction can trigger the growth of coronary plaque.8
A similar situation develops in the fragile penile circulation. Any disturbance in nitric oxide production lowers the capacity to dilate penile arteries, impairing penile engorgement for erection. Release of nitric oxide is readily sabotaged by many conditions, including elevated levels of cholesterol, high blood pressure, increased triglycerides, smoking, metabolic syndrome and diabetes, and excessive consumption of dietary saturated fat.9 If an artery’s inner wall can’t produce nitric oxide, an abnormal constriction of the arteries to the penis follows, effectively choking off blood flow.
Disruption in Nitric Oxide Synthesis
The body’s source for nitric oxide production is the amino acid L-arginine, which is naturally found in many foods. The average American ingests about 3,000–5,000 mg of L-arginine per day, as it is an amino acid naturally contained in many foods. Meats of all varieties, nuts, and dairy products are rich in L-arginine, so the body is accustomed to intake levels of several thousand milligrams every day.
A deficiency of L-arginine, however, does not generally disrupt nitric oxide synthesis because L-arginine availability is not the rate-limiting step in this process. In fact, research over the past five years has identified an endogenous (occurs in the body naturally) inhibitor called “asymmetric dimethylarginine” or ADMA, an amino acid which blocks the production of nitric oxide. By acting as an L-arginine mimic, this damaging look-alike effectively elbows out L-arginine and pushes it off to the side in the biochemical pathway leading to the synthesis of nitric oxide. ADMA is relatively elevated in patients with hypertension, high levels of cholesterol, triglycerides, homocysteine and low-density lipoprotein (LDL), and low levels of high-density lipoprotein (HDL), as well as with aging itself. This inhibitor of nitric oxide synthesis may very well be the common factor shared by all of these abnormal conditions. Increased levels of this detrimental inhibitor (ADMA) block nitric oxide production, leading to endothelial dysfunction.
Impact of Metabolic Syndrome
A collection of risk factors that strongly predict heart disease—termed the metabolic syndrome—is also associated with erectile dysfunction. An increasingly prevalent condition, this syndrome includes low HDL, increased triglycerides, high blood sugar, and heightened inflammation and causes a three-fold or greater risk of heart attack, stroke, and diabetes. It is largely attributable to excess weight, poor diet, and inactivity and afflicts at least 47 million Americans, signaling that an epidemic of erectile dysfunction is sure to follow. Indeed, a survey of 2,400 men participating in a health screening revealed that metabolic syndrome increases the likelihood of erectile dysfunction by 48%.10
Metabolic syndrome is characterized by HDL below 50 mg/dL in women, below 40 mg/dL in men; triglycerides above 150 mg/dL; blood pressure above 130/85 mm Hg; excess abdominal girth, and fasting blood sugar above 100 mg/dL. The likelihood of developing metabolic syndrome escalates sharply above a body mass index (BMI) of 27.
To make matters worse, men with features of the metabolic syndrome are far more likely to have low levels of testosterone, the primary male sex hormone.11 Obesity is also associated with reduced testosterone levels; the greater the excess body weight, the lower the testosterone.12
Declining Testosterone Levels
Low testosterone represents another link between erectile dysfunction and heart disease. A man’s testosterone levels gradually diminish beginning at age 30. By the time he reaches his 70s, testosterone levels may have dropped to a tenth of youthful levels. Diminishing testosterone levels contribute to loss of muscle, increased body fat, and reduced libido. Fatigue is common, as is depression. Low testosterone levels can also result in reduced concentration, irritability, passivity, loss of interest in activities, and even hypochondria.
Some call the transition period of the mid-40s the “male menopause” or “andropause.” The changes are indeed distinct, though not as visible as the female menopause. As there is no external cue comparable to cessation of a woman’s menstrual cycle, most men simply dismiss the changes as “getting old.”
Testosterone replacement can help to reverse many of the manifestations of reduced testosterone, boosting muscle strength and vigor, restoring lost libido, and helping control weight.13
Potential benefits of testosterone replacement in men with low starting levels include:
- Relaxation of vascular tone and partial correction of endothelial dysfunction. This may occur because testosterone increases production of the natural arterial dilator, nitric oxide, and suppresses growth of smooth muscle cells (a constituent of coronary plaques) in arteries.14
- Improvement in insulin resistance—a critical problem in pre-diabetes and the metabolic syndrome.15,16
- A dramatic reduction in inflammatory proteins such as tumor necrosis factor-alpha and interleukin-1beta.17
Low testosterone levels have been found to be more common in men with heart disease. In one study, men with confirmed heart disease had lower testosterone levels than healthy control subjects, whereas those with the most severe heart disease had the lowest levels of testosterone.18
Severe testosterone deficiency, known as “hypogonadism,” is present in approximately 2–35% of men with erectile dysfunction.19 However, lesser degrees of deficiency are common, perhaps present in the majority, depending on the definition of “low” applied, the method of measurement, and the parameter being used to define testosterone (total, free, or bioavailable) deficiency.19,20 Most authorities agree that a total testosterone level below 300 ng/dL is clearly low, and that 300–400 ng/dL is low to low-to-normal. Most studies using testosterone replacement for erectile dysfunction have attempted to achieve blood levels of 450–850 ng/dL.
In years past, before nitric oxide and its role in the erectile response was appreciated, testosterone was used to treat sexual dysfunction in men. It proved a partial success as a standalone therapy, resulting in improved erectile potency in 40–60% of men with low-to-normal testosterone levels. The likelihood of success increased, however, if starting testosterone levels were low (usually defined as below 300 ng/dL), in which case improved erections were experienced by as many as 65% of men, compared with 16.7% receiving placebo; topical testosterone preparations were also noted to be superior to oral replacement or injections.21 These findings were confirmed by another study that showed testosterone produced modest improvements in erectile function and libido in men with low-to-normal testosterone levels.22
Now that we better appreciate the complex sequence of events necessary for erections to occur, it’s no surprise that testosterone alone yields less than perfect results. Erectile dysfunction represents more than just low testosterone, which is just one facet of the spectrum of dysfunctional phenomena that cause sexual dysfunction. Nonetheless, when testosterone is combined with popular drugs like Viagra®, success is enhanced to an even greater degree—orgasmic function improves, along with erectile capacity and libido.20 Testosterone also activates penile nitric oxide; ultrasound studies have demonstrated a 27% increase in arterial blood flow into the penis with testosterone supplementation.23