The production of one of these protein substances, brain-derived neurotrophic factor, or BDNF, is increased not only by cerebral activity but also by aerobic exercise, and a few more words will be said about this later in the book. For now, it is enough to point out that the joggers you are accustomed to seeing or accompanying through the streets and byways of your community are doing far more than merely burning calories and improving their cardiovascular function. They are improving their minds as well, just as if they were reading a volume of Aristotle. Joggers, readers, thinkers, and doers of every stripe are influencing the aging process and healthy functioning of the human brain by taking advantage of its ability to change with use, and ever to expand its possibilities.
But of course, the joggers are doing their thing because they want to increase the capacity of their cardiovascular systems, probably not realizing how much smarter they are getting while huffing and puffing in the interests of staving off the aging changes that are trying to overtake their hearts and blood vessels. Those changes are far less complex than the ones trying to make headway in the brain. Though the frequencies of arteriosclerosis and hypertension are generally high in the elderly, many people reach their eighties and nineties with little or no disease of the heart or major arteries. As with all other parts of the body, there is great variation in how an individual’s heart and arteries may be affected by aging, ranging from the barely affected to the severely compromised. The following description pertains to what the average person can expect.
Perhaps more than is true for most systems other than the brain, lifetime habits are crucial determinants of the condition of one’s heart and arteries. Not unexpectedly, the most profound influences are due to those well-known factors—here they come again—of diet, obesity, smoking, physical activity, cholesterol level, and personality. Chronic diseases, of which hypertension and diabetes are among the most prominent, also play a major and often determining role.
In the absence of significant comorbidity, the aging heart and blood vessels manage astonishingly well. They are able to compensate so effectively for the normal anatomic and physiologic alterations of the years that, under ordinary circumstances, there is neither decrease in cardiac output nor abnormality of heart rate when at rest or when engaging in non-stressing activities. Among those normal alterations of aging are a gradual loss of elasticity in the major vessels, particularly the aorta, which is the large artery leading directly out of the heart. This decreased elasticity—caused in large part by the aggregation of protein strands into the cross-links mentioned earlier—causes the aorta to become wider and to elongate somewhat, thereby adding to its dimensions and forcing the heart to work harder in order to drive blood through its greater capaciousness. At first, the heart can compensate quite well for the increased work without raising the blood pressure required to do the job, but this begins to change slowly at about age sixty. Around this time, the heart begins to enlarge a bit, and the average systolic (upper number) blood pressure starts creeping upward from a normal of approximately 120 to a level of 140 for a healthy seventy-year-old.
Such numbers can merge into the pathological range, so that 15 percent of Caucasians and 25 percent of African Americans are hypertensive by the time they are sixty-five. Beyond that age, the figure is 1 in 4 for Caucasians and 1 in 3 for African Americans. Some surveys provide figures even higher than these. Of the several reasons why the increased pressure is dangerous, one is its tendency to cause damage to the lining of small blood vessels in the brain, leading to such problems as cognitive defects, stroke, and dementia.
In a normally aging heart, increasing amounts of fibrous tissue gradually begin to appear between the organ’s muscle cells, which are themselves slowly decreasing in number, so that by age seventy about a third of these muscle cells have been lost. At the same time, the number of the heart’s nerve cells, and their interconnecting fibers, is going down, so transmission of the electrical signals that trigger the heartbeat becomes less efficient, causing the organ to slow somewhat with age and eject less blood with each passing year.
Despite these losses, the mechanisms continue to function well so long as they are not subjected to stress. The older organ’s difference from a younger, normal heart is not apparent unless a challenge of some sort takes place, such as the need to run in order to catch a train, or perhaps the sudden emotional upheaval of anxiety or anger. In such situations, the aging ventricles are not able to accommodate efficiently. For example, older people are not nearly as able to vary their heart rate as they were when they were younger. Accordingly, the heart rate cannot increase as rapidly or as much in response to exercise. Also, after the rate does become elevated, it takes longer to return to baseline level. (A good rule of thumb is that 220 minus one’s age is the maximum heart rate that can be attained with vigorous exercise.) This means that the heart’s output is adapting less effectively than it once did to sudden needs that may be imposed on it.
It is for these reasons that a continued high level of activity is so important. Cardiac efficiency under conditions of stress can be markedly improved by exercise training. A heart that has been benefited by a consistent schedule of vigorous exertion can respond to stress like a heart several decades younger, not only by its added ability to beat more forcefully and faster, but also by the capacity of its muscle cells to take up the required supplemental supply of oxygen from the blood. This ability is aided by the effect of an exercise program on the chest wall. Because the chest wall becomes stiffer with age and its muscles weaken, general respiratory function lessens. But these changes are to a significant extent reduced by a vigorous program of aerobic exercise, which provides the added oxygen required by the stressed heart.
Exercise training also contributes other benefits for the cardiovascular system. Training improves the ability of the larger arteries to adapt to the heightened blood flow required by exertion, and it increases the sensitivity of certain pressure-monitoring structures—called baroreceptors—in the arterial walls. This is particularly important because normal aging causes (1) a decrease in blood flow through the thickening and less elastic middle-size arteries such as those to the kidney and liver; (2) a lessening of the number of capillaries throughout the body; (3) a narrowing in the diameter of the larger veins; and (4) a thickening and loss of elasticity of the heart’s valves, as well as some deposition of calcium in the valves’ leaflets. And, of course, the extent of arteriosclerosis—hardening of the arteries—is imperceptibly increasing all the time. Improved biological self-monitoring of pressure and flow leads to improved responsiveness in these structures when stress occurs. Planned vigorous exercise is a far better anti-aging treatment than all the elixirs, creams, lotions, potions, and cosmetic surgery in the world.
The various cardiac and vascular alterations described in the foregoing paragraphs occur even in the absence of any significant arteriosclerosis or hypertension. The addition of either of these pathologies results in worsening cardiovascular function, depending on the degree to which the pathology is present. But even under such circumstances of disease, response to stress can be improved with carefully graded exercise programs. Clearly, the physical workouts of men or women who have suffered heart attacks require meticulous oversight by their physicians. This is true not only on account of the danger of overstress but also because the older coronary arteries have lost some of their ability to make new collateral vessels to replace those that have become obstructed. This formation of new vessels is called angiogenesis.
But the most remarkable characteristics of the cardiovascular system’s response to aging are the two already mentioned, which it shares with all other organs and tissues of the body: its extreme variability from one person to another and its continuing competence to do its job perfectly well under normal conditions, even when it can no longer deal as effectively with major challenges.
Another example of this sort of thing is found in the functioning of the body’s hormones and the structures that
produce them, called endocrine glands. Here too certain of the aging changes occur to varying degrees in virtually everyone, while others of the aging changes are less universal. The first category involves a decreased ability of the intestine to absorb calcium, and so the amount of that mineral in the blood tends to become lower. In an attempt to keep the level steady, the parathyroids—glands buried deep within the thyroid, whose function is to control calcium metabolism—raise their output of hormone (called parathyroid hormone, or PTH), which has the effect of drawing calcium out of the bones and into the bloodstream. The lowered concentration of calcium in the bones worsens osteoporosis, which is already being caused by a combination of (1) certain aging changes in the cells that manufacture bone and (2) the loss of significant numbers of these cells. The decreased bone density that is the result of these two factors produces few or no symptoms unless the decrease becomes advanced. Because men have higher bone density than women and also because postmenopausal deficiency of estrogen causes bone loss (the reasons why are unclear), osteoporosis tends to be more severe in women, though men are hardly free of varying degrees of it, sometimes to the point of debility. Depending on the criteria for its diagnosis, about a third of men beyond the age of seventy-five are found to have osteoporosis. Not only the severity but the frequency of osteoporosis is more marked in women, by a factor that some estimate to be as high as 4 to 1. As with the body’s other aging mechanisms, individual variation results in a wide spectrum of how a person may be affected by this condition.
One’s position on that spectrum is influenced by physical activity. The more stress put on a bone by the forces of the muscle attached to it, the more its cells respond by doing all they can to maintain and even add to bone mass and strength, including increasing the absorption of calcium from the bloodstream. Just as a sedentary life encourages the loss of bone, a vigorously active life encourages increase in bone density.
Like disease of the cardiovascular system, loss of bone density can be managed by a variety of means in addition to exercise; the choice depends on the cause or causes thought to be most significant. Oral supplements of calcium and the vitamin D that increases calcium’s absorption from the intestine should be a standard part of the daily diet, beginning perhaps in one’s early fifties. The vitamin D becomes more important with the passing of years, to counteract the age-associated decrease of the vitamin in the body.
Because age-related loss of bone density is ultimately the result of a complex of changes at the level of the cell’s ability to make new bone, it is particularly important to combat the loss in the ways just described, with the addition of estrogen replacement therapy for women so long as there are no contraindications to its use in any given individual. Of course, other therapies of a pharmaceutical nature are available should osteoporosis become severe enough to require treatment, including those that bind with estrogens and influence their activity.
Though all of the body’s systems lose elements of function as the years pass, it is in the muscles and bones that major problems are likely to be most frequent, and these problems are almost as obvious as such developments are in an organ as visible as the skin. Among the most obvious changes is the decrease in muscle and the increase in fat. Musculoskeletal inadequacy is the single most common cause of debility in the old. Largely because of a decreased ability to manufacture the necessary protein, muscle mass lessens, a process that speeds up after the age of fifty. But contractile force decreases out of proportion to that change, probably as a result of some general alteration in neural signaling and coordination of fibers. By age sixty-five or seventy, about one-third of muscle strength has been lost, with loss becoming more rapid as the years add up. This seems to be due to a combination of fewer muscle fibers, the decreased size of each fiber, and a lessened ability of the fibers to function in a coordinated manner. As will be discussed later in this book, strength can be improved markedly with weight training, so much so that the muscle strength of a determined older man or woman can often be brought to a level comparable to that of a much younger person.
Falls become an increasingly important source of disability as people get older. Falls happen not only because of decreased strength and coordination but also because of a lessened range of joint motion and because of a generally decreased reaction time. All of these factors are accentuated by the kinds of neurologic deficits that sometimes make walking so hazardous. Improvements in coordination, muscle strength, and reaction time not only make falls less common, but also have the added benefit of increasing the likelihood that one will be able to control a fall sufficiently to lower the probability of fracturing a bone or dislocating a joint.
Here it seems appropriate to insert a parenthetical word about alcohol intake. Though strong evidence exists that the consumption of small to moderate amounts of alcohol, especially red wine, exerts protective effects on the incidence of strokes, coronary heart disease, gallstones, infections, and even the common cold, this should not be interpreted as a warrant to drink beyond such reasonable amounts. In the elderly, even the smallest degree of tipsiness markedly increases the frequency of falls and fractures, which means that a degree of circumspection and prudence is required each time a drink is considered. Not only that, but just a bit of euphoria impairs the judgment required to safely drive a car, especially for the elderly. These caveats are complicated by the fact that older drivers are more likely to be seriously injured than their younger counterparts experiencing similar types of auto accidents. And, of course, they are less likely to recover. In addition, one should account for the possibility of harmful interactions with the drugs that people beyond certain ages are more likely to be taking. The time for judgment is before drinking and not when it is too late.
Just as the preservation or rebuilding of muscle and bone are to a considerable extent determined by relatively simple measures, their opposites—loss of density and strength—are to a considerable extent determined by expectations. If one’s image of aging involves an inactive and generally sedentary existence, his or her punishment will be unnecessary loss of muscle and bone, leading to even less activity; if one’s image of aging involves vigorous participation in a variety of enthusiasms, his or her reward will be a gain of muscle and bone, allowing even more activity. In such ways, assumptions about the aging process become self-fulfilling prophecies.
The decreased estrogen levels that contribute to osteoporosis and other problems in postmenopausal women appear relatively rapidly. Men, on the other hand, lose testicular function gradually—so gradually that some men never become markedly deficient. Occasional octogenarians and even nonagenarians continue to have blood levels of testosterone that would be normal for a young adult. Unfortunately, this does not necessarily translate into retained libido and sexual potency.
Libido and sexual potency—has there ever been a man who did not give a thought to their decline with the years? Has there ever been a woman who did not wonder whether her libido or lack of it was “normal” for her age? Cicero, in his oft-quoted dissertation on aging, de Senectute, disposed of the entire matter by asserting that older people are well rid of their need for sensual pleasure, which “is a foe to reason, and, so to speak, blinds the eyes of the mind.” At the age of sixty-three, he felt himself happy to be free of its demands. “Far from being a charge against old age, that it does not much feel the want of any [sexual] pleasures, it is its highest praise.” Today, far fewer would agree with the Roman sage than protest that he had things all wrong. Though many elderly men and women feel that their sexuality is a thing of the past, many more continue to be active or continue to wish hopefully that circumstances allowed them to partake of what Cicero called a “deadly curse.”
Statistics about sexual behavior in the older population are hard to come by (no pun is here intended, and certainly not a double one) and notoriously unreliable. There are numerous reasons for this, but suffice it to say that no one should become discouraged by statements either of continued desire
and activity or of the opposite: lack of interest or ability to achieve any degree of satisfaction. Not only is there vast unreliability in the design of published studies done by surveys and suppositions, but even those experts most skilled in various areas of geriatric science and sociology seem to lose themselves in enthusiastic encouragement when writing about sex. An example of this is found in the standard academic text in the specialty of geriatrics and its associated research, a perfectly wonderful 1648-page volume compiled by five distinguished editors and no fewer than 207 authoritative contributors. Few would disagree that there is no more useful or reliable volume on the clinical and scientific aspects of the subject than Principles of Geriatric Medicine & Gerontology. But the second sentence of the book’s chapter entitled “Sexuality and Aging” unequivocally states, “It is reassuring to know that aging itself does not lead to sexual problems.” The chapter’s two authors—one of whom is, with very good reason, among the world’s most highly respected leaders in the field of aging—then go on to describe (with the clarity and wisdom that characterizes all of their other writings) all manner of obstacles to the kind of sexual functioning to which most men and women are accustomed during their earlier years.
It seems apparent from reading any significant amount of the pertinent medical literature and from virtually everyone’s personal experience that sex at seventy is a very different thing from sex at thirty-five, or even at sixty. And there are plenty of physiological reasons for the differences. The most obvious ones are related to the general lessening of male hormone levels in men and the marked decline of female hormones in women. Though an occasional elderly man, as noted above, is found to have testosterone levels equivalent to those of a thirty-year-old, such a thing is highly unusual and its significance uncertain. As for estrogens, they drop steeply during menopause. These and other physiological manifestations of aging have significant consequences for both desire and the nature of activity. To not call them problems is to deny their very real effect on lovemaking.
The Art of Aging Page 4