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By Katherine Hobson
At any age, sexual activity is an instinctive, automatic part of human behavior. But the biology behind that behavior is quite complex.
Americans are living longer than ever.
As the population ages, many senior citizens are burdened with chronic illnesses, but many others remain healthy and active. When scientists investigate aging, they have to distinguish between changes caused by disease and those caused by aging itself.
It's important research: among other things, it has taught us that men who take care of themselves can prevent many of the illnesses that make less prudent gents old before their time.
Until recently, research on aging has focused mainly on crucial things that go wrong — on heart disease, mental decline, arthritis, prostate woes, and the like. But while big-ticket items are still getting the priority they deserve, researchers are also expanding their horizons to include less critical issues.
Sexual activity is an important example.
Several reports shed light on aging and sexual activity, and one of them suggests that sex itself may help prevent sexual dysfunction in older men.
At any age, sexual activity is an instinctive, automatic part of human behavior. But the biology behind that behavior is quite complex.
Although the sex act is a continuous process, researchers have divided it into six stages. The first necessity is sexual desire or libido. The normal sex drive is a prime example of the unity of mind and body. It requires both an appropriate mindset and sufficient amounts of the male hormone testosterone. Sexual desires surface in puberty, when testosterone levels rise; although ardor tends to wane with age, most men produce enough testosterone to maintain libido throughout life. At any stage of life, however, worry, stress, or depression can thwart sexual interest, even if a man's physical apparatus remains intact.
Sexual activity itself begins with a state of arousal that results from various combinations of erotic thoughts and sensory stimulation that may involve the senses of touch, sight, scent, taste, or hearing. An area of the brain called the hypothalamus co-ordinates erotic images and sensations and transmits the impulses of desire through the spinal cord to the pelvis, where they link up with the nerves of the autonomic nervous system; sensory nerves from the skin of the penis and other erogenous zones connect directly to the autonomic nerves without involving the brain.
When properly stimulated, the autonomic nerves in the pelvis spring into action. They start the second stage of the male sexual response by transmitting chemical signals to the arteries of the penis, causing them to widen and admit more blood. Blood rushes into the two corpora cavernosa, shafts of spongy tissue that contain many vascular channels. The corpora cavernosa swell, producing an erection. The engorged corpora also put pressure on venules, compressing and narrowing them to prevent the extra blood from leaving, so the erection can be maintained.
For years, doctors have known that an erection is a hydraulic event that depends on a sixfold increase in the amount of blood in the penis. But research has revealed that an erection is also a chemical event. A tiny chemical called nitric oxide allows nerves to communicate with each other and with the arteries of the penis. Nitric oxide acts on the arteries through an intermediary called cyclic guanosine monophosphate (cGMP). It's been an exciting discovery for scientists, and it led to important progress for men with erectile dysfunction (ED) since the ED pills (Cialis, Levitra, and Viagra) act by boosting cGMP levels in the penis.
The third stage of sexual activity is called the plateau, which usually lasts from 30 seconds to two minutes. The heart rate and blood pressure rise as sexual activities continue, pumping more blood to the body's tissues. The penis is not the only recipient of increased blood flow; most men also experience facial flushing, and the testicles themselves swell by about 50%. During the plateau phase, the prostate and seminal vesicles begin to discharge fluid in preparation for ejaculation.
Sexual excitement climaxes with the fourth stage, ejaculation. The autonomic nervous system is in charge here, too. It tells the muscles in the epididymis, vas deferens, seminal vesicles, and prostate to contract, propelling semen forward. At the same time, nerve impulses tighten muscles in the neck of the bladder so that semen is forced out through the urethra instead of flowing back into the bladder. Ejaculation is usually accompanied by the pleasurable sensation of orgasm; in nearly all men, the heart rate reaches its peak during ejaculation.
All good things come to an end. The fifth stage of sexual activity is detumescence, when the penis returns to its flaccid state. Detumescence usually follows ejaculation, but it can occur prematurely if the sex act is interrupted by an intrusive thought or event. In either case, detumescence occurs when the penile arteries narrow and the veins widen, draining blood away from the organ.
The final stage in the sex act is the quietest. It's the refractory period, a span of 30 minutes (in younger men) to three hours (in older men) during which the penis cannot respond to sexual stimulation.
For many men, sexual activity is one of the things that change over time. It's usually a gradual, almost imperceptible process that begins in middle age.
Whereas most older men retain an interest in sex, it's generally a far cry from the preoccupation with sex that's so common in youth.
Although interest is retained, desire tends to wane; many older men think about sex, but don't have the drive to put theory into practice. And even when the spirit is willing, the flesh may be weak; male sexual performance typically declines more rapidly than either interest or desire.
Most men experience decreased sexual responsiveness with increasing age.
Erections occur more slowly, and they become more dependent on physical stimulation than on erotic thoughts. Even when erections develop, most men in their 60s report that their penile rigidity is diminished and harder to sustain. The ejaculatory phase also changes with age; the muscular contractions of orgasm are less intense, ejaculation is slower and less urgent, and semen volume declines. Sperm counts also decline; although healthy men can father children well into their senior years, their reproductive efficiency can't match younger men's.
Sexual intercourse requires a partner. But male sexual activity demonstrates age-related changes that are not dependent on interpersonal factors. Nighttime erections, which are normal events that occur during deep sleep, diminish with age; men between age 45 and 54 average 3.3 erections per night; between age 65 and 75, men average 2.3. Nocturnal erections also tend to become briefer and less rigid as men age.
Sexual activity is complex, and scientists don't understand all the factors that contribute to sexual function in young men, let alone what is responsible for the changes that occur with healthy aging. Still, it's clear that the hormones, nerves, and blood vessels responsible for male sexual activity all change over time. In the average man, levels of testosterone fall by about 1% per year beyond age 40 — but most older men still have enough testosterone to function sexually. To produce arousal, testosterone acts on part of the brain called the locus ceruleus, and these nerve cells become less hormone-responsive with age. Levels of estradiol, a predominantly female hormone, tend to decline with age; levels of another female hormone, prolactin, tend to rise. As for nerve function, penile responsiveness to sensory stimulation also slows with age. In addition, penile blood flow may decrease as men grow older, even if they stay healthy.
In men who stay well, all these changes add up to a gradual, partial decline in sexual activity. But in some men, the shift is more abrupt and complete. ED is closely linked to age. Only 5% of men under 40 years of age experience ED, but the prevalence rises steadily with age. About 44% of men in their 60s have ED, and the problem may affect up to 70% of American men over 70.
Because ED is so common in older men, many assume that it's part of the normal aging process. It's not. Instead, ED reflects the impact of chronic diseases that become increasingly prevalent with age. The most important are atherosclerosis and hypertension, which affect blood vessels, and diabetes, which strikes both blood vessels and nerves. In addition, stress, depression, and anxiety about adequate sexual performance can reduce sexual activity and satisfaction at any age. So too can marital strife, poor communication, poor sexual technique, and boredom; many of these problems become more common with age. Still, both partners in a relationship can expect to experience intimacy and sexual activity in maturity; if these expectations are not met, both people should explore the problems that may be responsible and the remedies that may be available. Important, too, are the medications that many older men require; numerous drugs can interfere with sexual function, including many used to treat high blood pressure, heart disease, anxiety, and depression.
Although you'd never guess it from late-night talk shows, TV ads for ED pills, or Mae West ("A hard man is good to find"), erectile dysfunction is not the only measure of successful male sexual activity. Two surveys of sexual activity in older men paint a more nuanced picture.
An American survey evaluated 1,455 men 57 to 85 years of age
Nearly 84% of men under 65 reported sexual activity with a partner during the year prior to the survey, but the figure fell to 67% in men between 65 and 74 and to 39% between 75 and 85 years of age. But among sexually active men, most reported at least two to three encounters per month throughout the three age ranges. There was little decline in sexual interest between ages 57 and 85, with over 70% of men maintaining interest. Confirming Shakespeare's insight ("Is it not strange that desire should so many years outlive performance?"), however, ED became more common over the years. In all, 14% of the men reported taking medication or supplements for sexual dysfunction.
A Swedish survey evaluated 225 70-year-old men
Among the men who were living with a partner, 66% reported sexual intercourse within the previous year; of these, 31% reported intercourse one or more times per week. More than half of all the 70-year- old men reported that sexual activity contributed to happy relationships.
In the age of Viagra, many men, young and old, respond to sexual dysfunction by downing a little blue pill or one of Viagra's newer rivals. Indeed, the ED pills have been a tremendous boon to male sexual activity, psychological health, and relationships.
But men with sexual dysfunction should always work with their doctors to identify underlying causes of the problem — and when the issue is ED, it's particularly important to identify and treat or correct cardiovascular risk factors, including abnormal cholesterol levels, high blood pressure, diabetes, tobacco abuse, obesity, and lack of exercise. In fact, ED is a powerful predictor of future heart disease, even in men who have no cardiac symptoms.
Although treatment can help remedy sexual dysfunction, prevention is surely the best medicine.
A 2003 Harvard study of 31,742 men between 53 and 90 emphasizes the preventive power of avoiding tobacco, getting regular exercise, staying lean, and avoiding excessive alcohol. And without contradicting these key instructions, a study suggests that sexual activity itself may help preserve erectile function in older men.
To find out if sexual intercourse protects against developing ED, scientists in Finland evaluated 989 men between 55 and 75
None of the men had ED when they volunteered for the study, and over 80% were married or living with a partner. Over the next five years, men who reported having intercourse less than once a week at the start of the study were more than twice as likely to develop ED as men who had intercourse weekly; they were also over four times more likely to develop ED than the men who reported having intercourse three times a week at the start of the study.
The study shows that men who are sexually active are less likely to develop ED than men who are less sexually active. But which is the horse and which the cart? Did increased sexual activity actually protect men from ED, or were men with good erectile function simply more active because they had better sexual function to begin with? The Finnish researchers tried to answer the question by evaluating the volunteers for problems that are linked to ED, including smoking, obesity, heart disease, high blood pressure, diabetes, depression, and cerebrovascular disease. Because they found little difference in ED risk factors among the groups, they argue that the crucial difference that protected against ED was sexual activity itself. Unfortunately, the study did not evaluate the possible impact of exercise, which lowers the risk of ED, or alcohol abuse, which raises risk.
The scientists offered a biological explanation for the apparent protective effect of sexual activity: erections bring oxygen-rich blood to the penis, perhaps preserving the health of tissues. It's the theory behind the still unproven practice of using ED pills for "penile rehabilitation" in men with ED following prostate surgery. It's an interesting theory, but more research is needed to see if it's right. Since healthy men have two to three erections each night, it's not clear that one to three acts of sexual intercourse per week would provide important extra benefit. The Finnish study did not evaluate nighttime erections, but it did report that the sexually active and less sexually active men had similar numbers of early morning erections.
Sexual activity is an important aspect of life, but its role changes over time.
Sex is necessary for procreation, which preserves the life of the species. And a healthy lifestyle is the best way to preserve sexual activity in seniority.
Most men remain interested in sex as they age, but many experience a diminished urge for sex and altered sexual function.
Despite these changes, healthy men should expect to retain the capacity for sexual activity and satisfaction throughout life.
The Finnish study suggests that regular sexual activity may help preserve erectile function as men age. Many men will welcome that finding, but more research is needed.
At present, the best way to preserve sexual activity is to preserve health; a good diet, regular exercise, and good health habits are the most effective ways to reduce the risk of developing the chronic diseases and requiring the medications that so often impair sexual activity.
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