The Merck Manual of Health and Aging: The Comprehensive Guide to the Changes and Challenges of Aging-For Older Adults and Those Who Care for and about Them

The Merck Manual of Health and Aging: The Comprehensive Guide to the Changes and Challenges of Aging-For Older Adults and Those Who Care for and about Them


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Product Details

ISBN-13: 9780345482747
Publisher: Random House Publishing Group
Publication date: 11/29/2005
Edition description: Comprehens
Pages: 992
Sales rank: 824,513
Product dimensions: 6.58(w) x 9.13(h) x 1.38(d)

About the Author

Merck & Co., Inc. is one of the world's largest pharmaceutical companies. It is committed to bringing out the best in medicine and, as a part of that effort, continues to proudly provide all of its famous Merck Manuals on a not-for-profit basis as a service to the community. The organization published the first of these in 1899, and by the 1980s, the series had become the world's largest selling medical text and was translated into more than a dozen languages.

Read an Excerpt

Age-Old Questions

Aging begins the moment a person is born. A baby develops and matures into an adult. Then, at some point, the aging process changes. The person begins a decline in function that ultimately leads to death—what people usually think of as aging or growing old. The technical term for this decline in function that ends in death is “senescence.”

Science can provide information about changes in the body that lead to aging and death. Science can determine how some of the changes occur. But two basic mysteries remain: whether aging and dying have a purpose and, if so, what that purpose is. Throughout history, people have responded to these mysteries by searching for a “fountain of youth” that will prolong the time spent as vigorous, healthy young adults. And the search continues as researchers look for ways to slow or reverse the aging process.

Some progress has been made in the search. During the last century, life expectancy for people in the United States has greatly increased. As a result, what people consider to be old age has changed dramatically. Improvements in life expectancy occurred in two stages. First, death during childhood has become less likely, largely because sanitation has improved and because vaccines and treatments for childhood diseases, such as antibiotics, were developed. Second, disease and disability have become less likely to develop or have been postponed in older people because health care and approaches to prevention have improved. In spite of these improvements, even the healthiest and luckiest people do not live beyond about age 130.

Looking for the Fountain of Youth

Books about how to stay young and live longer abound. Almost everyone is interested in living a long life and looking and feeling young. No Ponce de Leons are traveling to new lands on a search for a magic fountain to restore their youth. However, researchers are looking at genes, cells, hormones, eating patterns, and other factors for clues about what causes aging and how to prevent or slow it.

Research has identified three strategies that may help people live longer: exercising, following certain types of diets, and eating fewer calories.

People who exercise are healthier than those who do not. Exercise has many established health benefits: improving and maintaining the ability to function, maintaining a healthy weight, and helping prevent or postpone disorders such as coronary artery disease and diabetes.

People who eat a low-fat diet that includes lots of fruits and vegetables are healthier than people who eat more fat and starch. Also, people who live in Mediterranean countries and consume the so-called Mediterranean diet seem to live longer. This diet is generally thought to be healthier than northern European and American diets because it consists of more grains, fruits, vegetables, legumes, nuts, and fish and less red meat. In addition, the main fat consumed is olive oil. Olive oil contains many vitamins and consists mainly of monounsaturated fat rather than saturated fat. Monounsaturated fats do not increase cholesterol the way saturated fats do.

A low-calorie diet over a lifetime may lead to longer life because it reduces the number of certain damaging substances in the body. These substances, called free radicals, are by-products of the normal activity of cells. The damage done to cells by free radicals is thought to contribute to aging and to disorders such as coronary artery disease and cancer. But no studies to test this theory have been done in people.

These three strategies would require a change in lifestyle for most people. Consequently, many people look for other, less demanding ways to prevent or slow aging. For example, they may look for other ways to manage free radicals. Substances called antioxidants can neutralize free radicals and thus help prevent damage to cells. Vitamins C and E are antioxidants. So some people take large amounts of these vitamins as supplements in the hope of slowing the aging process. Other antioxidants, such as beta-carotene (a form of vitamin A), are also sometimes taken as supplements. In theory, the use of antioxidants to prevent aging makes sense. However, no studies have shown that antioxidants prevent or slow aging.

Levels of some hormones decrease as people age. Another way people try to delay or slow aging is to take supplements of these hormones. Examples are testosterone, estrogen, DHEA (dehydroepiandrosterone), human growth hormone, and melatonin. But whether hormonal supplements have any effect on aging is unknown. Furthermore, some of these supplements have known risks.

Some people believe that Eastern practices, such as yoga, tai chi, and qigong, can prolong life. These practices are based on the principle that health involves the whole person (physical, emotional, mental, and spiritual) and balance within the body. The practices may include relaxation, breathing techniques, diet, and meditation as well as exercise. They are safe for older people and probably improve their health. But whether these practices prolong life is difficult to prove.

When Does a Person Become Old?

The traditional designation for old age—65 years—has no basis in biology. Many people are vigorous and active at 65. Others are sick and inactive at 40. Rather, the basis for choosing age 65 is in history. Age 65 was chosen as the age for retirement in Germany, the first nation to establish a retirement program. (In 1889, Bismarck, Germany’s Chancellor, first chose age 70, but in 1916, the age was lowered to 65.)

The question as to when a person becomes old can be answered in different ways. Chronologic age is based solely on the passage of time. It is a person’s age in years. Chronologic age has limited significance in terms of health. Nonetheless, the likelihood of developing a health problem increases as people age. Because chronologic age helps predict many health problems, it has some legal and financial uses. It is also used to determine eligibility for some programs for older people.

Biological age refers to changes in the body that commonly occur as people age. For example, vision and hearing typically worsen as people age. Because these changes affect some people more than others, some people are biologically old at 40, and others are biologically young at 60 and even older.

Psychologic age is based on how people act and feel. For example, an 80-year-old who works, plans, looks forward to future events, and participates in many activities is considered psychologically young. Such a person is commonly described as “being young at heart.”

People often wonder whether what they are experiencing as they age is normal or abnormal. Although people age somewhat differently, many changes occur in almost everyone and are thus considered “normal.” However, a more accurate description of these changes is “usual.” Usual aging refers to what happens to most people, including disorders that are common among older people. Usual aging does not necessarily mean that the changes are unavoidable or desirable.

Usual aging was once thought to include such unavoidable changes as muscle weakness, slowed movement, loss of balance, and memory loss. Research has shown that many of these common, “normal” changes result from an unhealthy lifestyle or from disorders that can be prevented or treated and reversed, rather than from aging itself. So the question to ask may be whether changes can be avoided rather than whether they are “normal.” This question leads to the concept of healthy aging.

Healthy aging refers to a postponement of or reduction in the undesired effects of aging. The goals of healthy aging are maintaining physical and mental health, avoiding disorders, and remaining active and independent. For most people, maintaining general good health requires more effort as they age. Certain healthy habits have been shown to reduce the risk of developing several disorders that commonly occur as people age. These habits include following a nutritious diet, exercising regularly, and staying mentally active. Developing these habits is an important part of healthy aging. The sooner a person develops them, the better. However, it is never too late to begin.1 In this way, people can have some control over what happens to them as they age.

Why Does the Body Change?

The body changes with aging because changes occur in individual cells and in whole organs. These changes result in changes in function, in appearance, and thus in the experience of aging.

Aging Cells

As cells age, they function less well. Eventually, they must die, as a normal part of the body’s functioning.

Cells may die because they do not divide normally or because they are damaged. Cells may be damaged by harmful substances in the environment, such as radiation, sunlight, and

1. see page 33

chemotherapy drugs. Cells may also be damaged by certain by-

products of their own normal activities. These by-products, called free radicals, are given off when cells produce energy.

Many cells die because the genes they contain program a process that, when triggered, results in death of the cell. This programmed death, called apoptosis, is a kind of cell suicide. Reasons for cell suicide include replacing old cells with new ones and eliminating excess cells.

Also, cells die because they can divide only a limited number of times. This limit is also programmed by genes. When a cell can no longer divide, it grows larger, exists for a while, then dies. The mechanism that limits cell division involves a structure called a telomere. Telomeres are used to move the cell’s genetic material in preparation for cell division. Every time a cell divides, the telomeres shorten a bit. Eventually, the telomeres become so short that the cell can no longer divide. The telomeres of cancer cells, unlike those of normal cells, do not shorten each time the cell divides. Consequently, cancer cells can divide forever.

Aging Organs

How well organs function depends on how well the cells within them function. Older cells function less well. Also, in some organs, cells die and are not replaced, so the number of cells decreases. The number of cells in the testes, ovaries, liver, and kidneys decreases markedly as the body ages. When the number of cells becomes too low, an organ cannot function normally. Thus, most organs function less well as people age. However, not all organs lose a large number of cells. The brain is one example. Healthy older people do not lose many brain cells. Substantial losses occur mainly in people who have had strokes or who have Alzheimer’s disease or Parkinson’s disease.

A decline in one organ’s function, whether due to a disorder or to aging itself, can affect the function of another. For example, if atherosclerosis narrows blood vessels to the kidneys, the kidneys function less well because blood flow to them is decreased.

Why Does Function Decline?

For most people most of the time, the decline in organ function does not affect the body’s ability to function during normal daily activities. People usually notice the decline in organ function only when very demanding tasks are attempted or when a disorder develops. For example, the amount of blood pumped by the heart during vigorous exercise decreases as people age. Older people may notice this change only when they play tennis or jog, not when they take a walk. They may notice changes in brain function only when they try to learn new information, such as a new language.

A noticeable decline in function is more likely to result from factors other than aging itself. The most common culprit is a disorder. A disorder may cause pain or confusion, make movement more difficult, rob a person of energy, or lead to depression.

The psychologic, sociologic, and financial situation of older people affects their behavior. Their behavior, in turn, affects their ability to function. Fear or worry may cause older people to become less active. If older people are less active, their ability to function tends to decline. Older people may fear being hurt or embarrassed, so they withdraw from their favorite activities and stay home. Older people with balance problems may fear that they might fall and break a bone. Older people with urinary incontinence may worry that they could have a wetting accident. Not having a partner with whom to share experiences or not having adequate funds may also stop people from participating in activities. People who participate in meaningful activities tend to remain healthy and live longer, as do people who have social support (married men in particular), adequate funds (those in a higher socioeconomic bracket), and a higher educational level.

Taking preventive measures can help older people remain healthy, active, and able to function.1 Older people can develop healthy habits and continue to participate in activities. Learning to recognize situations and tendencies (such as fear) that can lead to further problems can help. Having a positive attitude toward aging—expecting life to continue to be full, hopeful, and worthwhile—can also help.

If older people remain fit and well, they do not lose their ability to remember, learn, think, and reason. They can remain physically active and capable. They can adapt to change. They can resist most disorders. When they develop a disorder, they can tolerate and respond to medical and surgical treatments and usually recover.

From the Paperback edition.

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