As America’s “baby boomers” move into middle age and more people live well beyond their 60’s, researchers are exploring why the body ages and how we might fend off aging’s effects. The general advice of physicians today on how to stave off the effects of aging has not changed much since 1822 when the English physician William Kitchiner prescribed behavior for “The Art of Invigorating and Prolonging Life”:
“Go to bed early, rise early. Take enough exercise as you can in the open air, without fatigue. Eat and drink moderately of plain and nourishing food. And especially, keep the mind diverted, and in as easy and cheerful a state as possible.”
But people today live much longer than they were in 1822 when most people could expect to live until about their mid-40’s. According to the National Center for Health Statistics, in the United States alone, the overall life expectancy (the average number of years a newborn is expected to live) has increased from 47 years in 1900 to 75 years in 1992. And the most significant increases in the average longevity of human beings had come about only since the early 1900s, when sanitation, nutrition, and medical care improved significantly, at least among developed nations.
This longer life expectancy has resulted in a growing elderly population. The U.S. Bureau of the Census reported in 1992 that 32 million people—or about 1 in 8 Americans—were over the age of 65. By the year 2035, the Census Bureau estimates that 1 in 4 Americans will be over age 65. Most scientists think that there is a biological limit to life—perhaps between 115 and 120 years—and that the ultimate average life expectancy is about 85 years. But others see no end in sight.
What Are The Effects Of Aging
Although the external signs of aging—gray hair, baldness, wrinkles, “age spots”—may distress people, it is the internal changes that can rob a person’s vigor. Generally, as people age, muscle mass diminishes, the body’s disease-fighting immune system becomes less efficient, and the heart and lungs become vulnerable to disease. The risk of cancer and other illnesses also increases. The physiological changes caused by aging eventually catch up with everyone who lives long enough. But the extent and timing of these changes vary considerably from one person to the next.
Some of the aging’s effects also differ in men and women. At about age 50, women experience menopause, the time when fertility and menstruation cease. Levels of the female hormone estrogen fall, while the levels of some other hormones rise. The drop in estrogen levels can make women become anxious and depressed and experience hot flashes (a sudden feeling of heat accompanied by dilation of the blood vessels and sweating). It can also contribute to osteoporosis (a decrease in bone density resulting in fractures, especially of the spinal vertebrae, hip, pelvis, and forearm).
In men, aging’s effect on the male hormone testosterone is less dramatic than the hormonal changes that occur in women. Although testosterone levels decrease with age, researchers have yet to determine the cause, effects, and extent of this decline.
Because most people now live a long life and must face the many changes that aging brings, researchers are devoting a great deal of effort to exploring antiaging methods. Some of their findings have resulted in a reaffirmation of the rewards of a healthy lifestyle, while others have led to the introduction of experimental treatments.
Does Nutrition Fight Aging
Reports published during 1991 and 1992 variously announced that some substance in broccoli seems to ward off cancer; vitamin C might protect senior citizens against heart disease and cataracts; vitamin E may boost the immune system of older people and reduce the build-up of fatty deposits in arteries; and vitamin B12 may help prevent senility (loss of intellectual faculties, beginning for the first time in old age).
Although such findings are encouraging, many experts believe that consuming significantly higher amounts of these vitamins is premature since long-term consequences of higher doses are unknown.
Nevertheless, doctors believe that the types of foods a person eats play an essential role in protecting against disease and other aging physical effects. For example, there is good evidence that adequate calcium intake can later reduce bone loss among older women. And numerous nutrition studies have indicated that a diet low in fat and high in fiber can decrease the risk of the two leading causes of death among senior citizens in the United States: cancer and cardiovascular (heart and blood vessel) disease.
In 1990, the National Institutes of Health (NIH) in Bethesda, Md., advised adults to consume low-fat diets, with a maximum of 30 percent of calories from fat. In 1991, the NIH made the same dietary recommendation for children as young as age 3. This advice was based largely on studies showing that plaque (fatty deposits that build up in arteries), which can lead to heart disease, can begin to form during childhood. In 1992, the U.S. Department of Agriculture issued new nutritional guidelines, suggesting that people should consume less fat by eating more fruits, grains, and vegetables—and less meat, dairy products, and oils.
Underscoring the new emphasis on nutrition’s role in maintaining health, the American Cancer Society in 1992 announced that it would commit more resources to research on nutrients that could prevent cancer. Many biogerontologists (researchers who study the biological processes associated with aging) and nutritionists believe that certain nutrients act as antioxidants, chemicals that may intercept and react with potentially damaging molecules called free radicals, and render them harmless. Among such antioxidants are beta-carotene (a substance the body turns into vitamin A) and vitamins C and E, all found in many fruits and vegetables.
Exercise For Anti Aging Not For Good Looks
Many studies show that aerobic or even moderate exercise can slow or reverse some effects of aging. For example, after an eight-year-long research on the impact of exercise on 13,344 men and women, researchers at the Institute for Aerobics in Dallas concluded in 1989 that walking briskly for only 30 minutes per day can prolong life and reduce the risk of death from heart disease and cancer.
In 1990, British scientists reported that middle-aged men who engaged in regular vigorous physical activity substantially reduced their heart attack risk. And researchers from the University of California at San Diego, who studied the effects of physical activity on more than 600 women aged 50 to 89 years, announced in February 1991 that moderate exercise significantly lowered blood pressure. High blood pressure is a significant risk factor for heart disease and stroke.
Furthermore, the benefits of physical activity can be reaped at any age. A 1990 study by gerontologist Maria Fiatarone at Harvard Medical School in Boston showed that exercise could benefit nursing-home residents over age 90. In just eight weeks of working out with weights, these older individuals increased their strength by 174 percent, boosted their walking speed by 48 percent, and pumped up their muscle mass an extra 9 percent.
There is also evidence that exercise may help prevent Type II diabetes—the most common form of diabetes mellitus. In this disorder, the body cannot respond efficiently to insulin, a hormone that is important in using and storing sugar. The risk of developing Type II diabetes increases with age, and complications can irreversibly damage the heart, blood vessels, kidneys, eyes, and nerves.
Researchers at the University of California at Berkeley in 1991 reported that among 6,000 healthy men, those who exercised the most vigorously were less than half as likely as those who were the least active to develop Type II diabetes. A study of 87,000 middle-aged women reported in June 1991 by researchers from Harvard Medical School came to similar conclusions.
Physical activity also helps fight depression by providing a psychological boost, and it may also help keep the mind functioning well. For example, research done at the Veterans Administration Medical Center in Salt Lake City, Utah, in 1984 found that a vigorous exercise regimen helped people between the ages of 55 and 70 improve their memory and response time on tests measuring mental abilities.
How To Maintain Intellectual Functioning
Findings that lifestyle factors may improve “mental fitness” are puncturing some long-standing myths about aging’s effects on the brain. Neurologists acknowledge that the brain loses some of its cells and shrinks somewhat with age, possibly causing memory impairment.
But the substantial mental decline is no longer considered an inevitable consequence of growing older. In fact, studies have shown that most older people who show marked signs of mental deterioration actually have some underlying disorder, such as depression or Alzheimer’s disease (a condition that causes profound mental deterioration).
In addition, scientists have revised their belief that the brain’s nerve cells cannot rejuvenate themselves. Researchers at the University of California at Irvine reported in 1991 that the brains of old rats were just as adept at repairing damaged nerve cells and growing new connections between them as were the brains of young rats.
Researchers have also found that when rats are kept isolated and sedentary, with nothing to interest them, the number of connections between the brain’s nerve cells declines. But when the animals are required to perform a complex task, such as finding their way through a maze, new connections sprout between their brain nerve cells. Researchers wonder whether mental stimulation might have a similar effect on the brains of human beings.
Can We Stop Aging
While some researchers seek ways to cope with aging, others are trying to understand the aging process itself, and they have proposed several hypotheses to explain this phenomenon. Genetic makeup (traits passed in genes from parents to their offspring) lies at the heart of a number of theories on aging.
Genes in the human body orchestrate growth and maturation and the maintenance and repair of cells. Studies have shown that these processes proceed simultaneously until about age 30. At that point, growth has stopped, and the body does not work as efficiently to repair or replace cells.
A cell’s genes tell the cell how and when to divide, and one theory of aging proposes that each of our many types of cells has a built-in limit to the number of times the cell can divide. Experiments to support this theory were first done in the 1960s by geneticists Leonard Hayflick and Paul Moorhead, then at the Wistar Institute in Philadelphia.
They reported that normal human embryo cells placed in laboratory cultures divided about 50 times before dying. Normal adult cells, however, divided only about 20 times. Hayflick’s experiment suggests that messages contained in genes control how long cells live, which may, in turn, dictate how long human bodies survive. Ironically, the only human cells that appear to be immortal—at least in laboratory cultures—are abnormal ones, such as cancer cells.
Because unusual longevity tends to run in families, some scientists believe that aging must have a genetic component. One theory holds that there are “aging genes” that determine the life span. But no one has pinpointed a gene or genes responsible for long life. However, researchers believe that the ongoing Human Genome Project, a massive international effort to identify all 50,000 to 100,000 human genes, is likely to turn up genes relevant to aging research. Therefore, to stop aging is out of control, but we can manage it and slow it to live the healthful life.
Aging Due To Genes Damage
Aging might reflect the accumulation of errors in genes, according to some biogerontologists. Researchers suggest that external factors, such as pollutants or radiation—including the cosmic rays (subatomic particles from space) that continually bombard the Earth—and even the oxygen we breathe, can cause these errors by damaging the components of genes.
Genes are made of DNA (deoxyribonucleic acid), and most genes contain the recipe to create proteins. If external factors damage a cell’s DNA, the recipe can become garbled, and the proteins the cell makes may be abnormal. This can have serious consequences because proteins regulate thousands of cell activities.
A cell with abnormal proteins may not be able to perform its particular task adequately, whether it is to fight infection, refurbish body parts, digest food, or communicate with other cells. Proteins also form much of the body’s structural material, such as muscle and cartilage (the tissue that supports bone and other organs). No one has been able to show that protein errors increase with time. However, such errors might occur in just a few key proteins that have yet to be examined.
Role Of Proteins in Aging
Other researchers suggest that we age because the body’s ability to handle proteins deteriorates. Studies indicate that as the body gets older, it produces certain proteins more slowly than it did in the past. Furthermore, the aging body becomes less efficient at clearing out old protein molecules. And the longer a protein hangs around, the more likely it is to react with a blood sugar called glucose or with other proteins.
This theory, first proposed in 1981 by scientists at Rockefeller University in New York City, suggests that this phenomenon, called cross-linking, gums up the cell and interferes with its normal functions. But scientists do not yet understand why the body becomes less efficient at making and removing proteins in the first place.
What is Free-Radical Theory
Another theory of cell aging holds that cells “rust” as a result of interactions with oxygen. Just as oxygen takes its toll on iron, interacting with and chewing up the surface to create rust, the oxygen that is continuously fed through the body may take its toll on tissues. Highly reactive free-radical molecules routinely form when the cell uses oxygen to produce energy.
Free radicals can also form in other ways, such as through radiation exposure. However, they form free radicals interest biogerontologists because they are loose chemical cannons that readily react with other cell molecules, and these reactions can damage proteins, DNA, fats, and other cell components. This theory was first proposed in the 1950s by aging specialist Denham Harman of the University of Nebraska, and it has become a popular explanation for disorders ranging from cancer to dandruff.
Some scientists think that free-radical damage to the cells of the immune system may explain the elderly’s increased susceptibility to disease. Although the body generates antioxidants that neutralize free radicals and prevent most of their damage, free radicals take their toll over time, according to the theory.
Can We Live Longer by Eating Less
Researchers have long sought ways to extend the life span of humans. So far, reducing food consumption is the only known method of extending the life span of animals. Experiments using dietary restriction date back to studies done in 1935 by nutrition researcher Clive McCay of Cornell University in Ithaca, N.Y.
McCay reported that when rats were fed only 25 percent to 40 percent of their usual calorie intake, their maximum life span increased by as much as 60 percent. A 1991 study at Tufts University in Boston found that mice lived 29 percent longer when their food intake was cut by 40 percent.
Researchers have also found that rodents on restricted diets have good immune systems, are leaner, and show a much lower cancer rate. Such diets seem to induce in them a period of daily torpor during which metabolism drops and body temperature falls. In addition, the restricted diets boosted levels of some natural antioxidants, which may reduce free-radical damage.
Roy Walford of the University of California at Los Angeles is among the gerontologists identified with the study of dietary restriction. On Sept. 26, 1991, Walford and seven other researchers entered Biosphere II, an experimental and controversial self-contained colony in Oracle, Ariz. Walford intends to keep the people in Biosphere II on a low-calorie, high-nutrient diet for the duration of their two-year stay.
Although Walford argues that humans could gradually adjust to severe caloric restriction, most people would probably find the chance at a longer life, not worth the price. However, if researchers can determine just how dietary restriction works to extend life span, they may be able to devise a way for people to get the benefits of the diet without the sacrifice of sticking to it.
Youthful Qualities In Hormones
Researchers have also long sought substances that can slow or even reverse the aging process. For example, physicians have prescribed estrogen for postmenopausal women since the 1950s to offset physical and emotional changes caused by menopause. In 1991, a large-scale study by researchers at Harvard Medical School confirmed earlier findings that estrogen supplements could help older women live longer by protecting them from coronary artery disease, the chief cause of death for women over 50.
Furthermore, a study reported in 1991 by researchers at the University of Southern California in Los Angeles found that the overall death rate for women who had used estrogen for more than 15 years had decreased by 40 percent, compared with the death rate for women who had not used the hormone.
However, estrogen supplements may increase the risk of endometrial cancer, a rare but often fatal type of cancer that affects the lining of the uterus. To lessen this hazard, physicians recommend either frequent screening for this cancer or taking a second hormone, progesterone, which counteracts estrogen’s effects on uterine tissue. Estrogen supplements have also been linked with an increased risk of breast cancer, but progesterone may lower this risk, as well.
What Are Agents Of Growth
Inspired by estrogen’s successful use, scientists are testing other types of hormones to determine whether they will help counteract the effects of aging. Human growth hormone has entered the antiaging research arena and has shown some dramatic results in human tests. Usually, the body produces growth hormones in varying amounts throughout its lifetime.
During childhood and young adulthood, this hormone promotes growth. In adults, it enhances the body’s use of nutrients and supports the action of other hormones. About one-third of elderly people produce diminished amounts of growth hormone and, therefore, may have diminished muscle strength, according to researchers.
Gerontologist Daniel Rudman of the Medical College of Wisconsin in Milwaukee and his colleagues in 1990 reported results of a study in which 12 older men were given a genetically engineered version of human growth hormone three times a week for six months. During that time, they experienced a 9 percent increase in muscle mass, a 14 percent decrease in fat, and a 7 percent increase in skin thickness.
Unfortunately, the treatment was not without side effects. About one-third of the men experienced water-weight gain, breast enlargement, or carpal tunnel syndrome (a painful condition of the hand and wrist). And the benefits did not last. After the treatment was discontinued, the new muscle turned back to flab.
Other hormones under investigation include DHEA (dehydroepiandrosterone), an androgen, or male hormone, that is naturally produced by the testes in males and by the adrenal glands in both sexes. This hormone diminishes with the years. In tests on aging mice, DHEA caused a decline in the number of mammary cancers, a delay in the immune system’s deterioration, and increased life span.
Doctors in Europe use the hormone to treat psychological stress. Limited trials of DHEA in humans were underway in 1992 at various research centers in the United States to determine whether it can decrease cancer and heart disease risk, reduce stress, build muscles, and increase infection-fighting cells. Scientists have just begun to study this hormone in depth, so it will be many years before its long-term effects—both positive and negative—are known.
Scientists also have begun testing neurotrophic growth factors, natural substances that nourish nerve cells. Researchers are hoping that these agents will rejuvenate shrunken or damaged nerve cells or promote the growth of new ones. They have found that different types of neurotrophic growth factors target different nerve cells, making it conceivable that genetically engineered versions of these substances could be used to treat specific diseases associated with the brain and nervous system. Such conditions include Alzheimer’s disease, Parkinson’s disease, and multiple sclerosis.
Impact of Fighting Aging In Society
Although the benefits of fighting aging are evident for individuals, the effects of a large aging population on society are more questionable. For example, an ever-aging American society may further strain the health care system and economy.
Nevertheless, the human desire to live longer and healthier lives is driving research that may help extend life and cure the diseases that plague us in our later years. By the time today’s children approach old age, 1 million Americans will probably be over the age of 100. If they take advantage of what is known now about turning back the clock on aging, those centenarians of tomorrow may live active lives right to the end, genuinely realizing the satisfactions the golden years can hold.