Introduction to Healthy Aging
Is it possible to extend your lifespan and become healthier in later years by changing behavior and seeking certain types of care? ABSOLUTELY!
All About Aging
The human life span has been growing dramatically. A person born in 1776 could expect to live 35 years. By the year 1900, the average life span was only 47 years. But a girl baby born today can expect to live 79 years, and a boy baby 72.
People who live to older ages have an even greater life expectancy. A woman who lives to 65 has another 18.9 years on average to live, and a woman who lives to age 85 will average another 6 years of life.
The centenarian club
The most dramatic increases have been in the number of people living to advanced old age. In 1900, only one out of every 100,000 people lived to be 100 years old; today, one out of every 8-10,000 people makes it to 100. Our population of centenarians is growing by 8% each year, as opposed to a growth rate of only 1% for the population at large. Today, there are 50,000 centenarians in the United States, but there are projected to be one million by the year 2050!
Life span predictions
Will the human life span continue to grow, until we have a country of Methusalahs? Probably not. Major increases in life expectancy in the early part of this century were due to decreases in the infant mortality rate, and advances in public health. But it has been more difficult to improve the survival rates of those with chronic diseases, which have dominated in modern times, and increases in life expectancy have been relatively flat over the past 10 years. Many aging experts project that the average human life span will not extend much beyond 85, without major breakthroughs in the biology of aging. Besides, most people's reaction to the idea of living to 100 is, "no thanks", unless they can be guaranteed that they will be vigorous, active, and mentally intact 100 year olds. The goal of "adding life to years" rather than simply "adding years to life" is what most people hope for.
Can we affect the aging process?
How realistic is it to hope that we can affect the aging process? Many people feel that life expectancy is "all in the genes", and that the aging process is little affected by our living habits. However, several scientific studies have looked at the aging processes of twins who were reared together and apart, in order to look at the contributions of genetics vs. living habits to longevity. Two famous twins' studies found that aging was less related to genetic factors than to lifestyle and health behaviors. So there is a lot of evidence that suggests that we can, indeed, affect the aging process.
Why Do We Age?
In order to understand how lifestyle and health habits can affect the aging process, it is important to try to understand why we age. No one entirely understands why we age, and there have been more than 300 theories proposed for the biological basis of aging. Many of the theories fit into two broad categories of aging theory. The first is the category of stochastic theories of aging, which basically state that age is a result of random damage to cells and organs over time. The second category of aging theories is that of programmed theories, which state that the aging and death of cells is genetically determined.
The stochastic theories of aging
The most prevalent of the stochastic theories is the free radical theory of aging. Free radical theory: This theory recognizes that metabolic reactions occurring continuously in the body produce unstable molecules called free radicals. Free radicals try to stabilize themselves by a process called oxidation, which damages elements of cells such as protein and DNA, the cells' genetic material. So oxidants, the products of this process by which free radicals become more stable, are considered to be the perpetrators of aging. The body has many natural anti-oxidant defenses, some with strange names like superoxide dismutase and glutathione peroxidase, and others whose common names are familiar, like ascorbate (Vitamin C), tocopherol (Vitamin E), and carotenoid (Vitamin A). So the "anti-oxidant vitamins" are touted for their anti-aging effects because they combat free radicals.
The "age spots" that accumulate on the bodies of many older people are made of lipofuscin, a pigment that contains numerous elements, including mercury, aluminum, iron, copper, and zinc. These elements are known to accelerate oxidative damage, so lipofuscin is correctly called the "aging pigment". Lipofuscin deposits in other, unseen parts of the body, such as the brain, are considered markers of aging.
The caloric restriction theory: Another view, associated with the free radical theory, is the theory of caloric restriction. Scientists have been able to prove in many species of animals, including rodents, fish, spiders, and water fleas, that reducing calories, while continuing to provide adequate nutrients, results in extension of the lifespan. The theory is that reducing the metabolism of calories reduces oxidative damage to cells. Experiments with primates, and with actual humans, are still underway. The extent of caloric deprivation necessary to extend lifespan in animals has been at least 40%. So a reasonable question for many people would be whether they were willing to give up 40% of their eating pleasure in the interests of a longer life!
Numerous studies have demonstrated an association between excessive weight and higher mortality, but the converse, that the thinnest people live the longest, has not been shown. This is probably because the thinnest people are sick with diseases or are undernourished.
So far, studies indicate that the lowest mortality rates are associated with a body mass index (BMI) in the 21-22 range. To calculate your own BMI:
- Convert your weight in pounds to kilograms by dividing your weight in pounds by 2.2.
- Multiple your height in inches by 0.0254 to get your height in meters.
- Multiply your height in meters by itself.
- Divide the answer to #1 by the answer to #3.
Plenty of evidence supports the programmed theories, which tie aging to genetic programming. Scientists back in the 1960's demonstrated that cells that replicate by dividing were only able to undergo a specific number of divisions before they became old and died. More recent advances in aging research have identified the cell's "aging clock" called the telomere. A telomere is a "tail" at the end of every chromosome (a strand of DNA) that shortens every time the chromosome replicates and divides. When the telomere reaches a critical shortness, the cell can no longer divide. In 1998, scientists made headlines by introducing into cells telomerase, an enzyme that prevented the telomere from shortening with each cell division, thereby extending the lifespan of the cell. Whether or not this exciting breakthrough can eventually be applied to extending human lifespan remains to be seen.
In fact, any hope of significantly extending the average human lifespan will probably depend on further progress in understanding the human genome and its influences on programmed cell aging and death.
The hormonal theory of aging
Another theory of aging, which has caused much activity and interest in the healthy aging movement, is the hormonal theory of aging. Numerous hormones, chemical substances secreted by various glands in the body, decline with aging, leading to speculation that replacement of these waning hormones may prevent the aging process. Hormones that are currently being touted as a means of combating aging include growth hormone, DHEA, melatonin, testosterone, and estrogen. Many people, in a quest for the fountain of youth, are taking growth hormone injections and enthusiastically ingesting other hormones. But does the evidence support their enthusiasm?
The answer is ... it remains to be seen. Human growth hormone was shown, in an exciting study in 1990, to increase muscle mass and bone density, and decrease fat in aging men. Since then, numerous studies have evaluated its efficacy in reversing aging in malnourished, frail, elderly, and critically ill persons. The results are mixed. Furthermore, it can only be given by injection, it has numerous potentially serious side effects like hypertension, heart failure, and diabetes, and it is enormously expensive. The annual price tag for weekly growth hormone injections can be as much as $15,000.
Testosterone, melatonin, DHEA, and estrogen
Similar questions remain about the long-term effectiveness of other hormones. Testosterone has definitely been shown to improve sexual performance in testosterone-deficient men. It can also help to control hot flashes and increase libido in postmenopausal women, and may increase strength in frail elderly. But its long-term effects are not known, and there is a concern about testosterone promoting the growth of prostate cancer. Melatonin has been shown to help regulate sleep, especially in jet-lagged travelers, but whether or not it can truly reverse aging and prevent cancer as promised has not been proven. Neither has DHEA, a hormone produced by the adrenal gland but also found in plants, been shown to reverse aging, or increase strength, energy, or libido, although some small studies suggest that it may help decrease depression. So the jury remains out on these highly-touted hormones.
Hormone Replacement Therapy Update
For five years, a major study called the Women's Health Initiative has been reviewing two types of hormone pills: estrogen alone, and a pill that combines estrogen and progestin. In June, 2002, study results revealed that the estrogen/progestin combination pill was resulting in more risk than benefit in the more than 16,000 women taking it. Results showed an increased risk of breast cancer, heart attacks, strokes and blood clots among women taking estrogen plus progestin. The portion of the study looking at patients taking estrogen alone is still ongoing. It is still uncertain whether the benefits of the hormone pill containing estrogen alone outweigh the risks.
The benefits of taking estrogen, in women at increased risk of osteoporosis or colon cancer, are still valid, however. It is important to discuss all choices regarding hormone replacement therapy at length with a healthcare provider before making a decision.
A Remarkable Study of Remarkable People
Researchers in Boston decided to investigate what helps people to live a long and healthy life by studying people who had successfully survived into "old old age". Drs. Thomas Perls and Margery Silver investigated 169 centenarians in the New England Centenarian Study. This remarkable group of men and women (85% female) had remained physically healthy and mentally alert well into their nineties. The personal attributes that were common to a great majority of these survivors included:
- low levels of depression.
- striking ability to cope with, and adapt to, stress and loss.
- high levels of intellectual stimulation.
- frequent use of humor as a coping mechanism.
- high levels of social interaction and support.
- nearly universal lack of obesity, excess alcohol, and smoking.
- preventing diseases
- reducing cellular damage
- avoiding aging caused by disuse
- genetic manipulation (potentially)