When the 21st century dawns in just a few years, one American in eight will be 65 years old or older. By 2030, the percentage of the population over age 65 is estimated to be 20 to 25 percent; that is one out of every four or five Americans. This is an enormous shift in population, perhaps the greatest in history, because the shift is occurring on every part of the globe. The magnitude of this change is emphasized when we realize that only 1 in 25 of our U.S. population was over the age of 65 in 1900.
This demographic shift presents our Nation with a most important challenge: the health and nutritional needs of a population that is growing older. Our food and food products will increasingly have to address the special needs of older Americans as they strive to maintain a high degree of function into old age. The goal is for the lives of older Americans to be not only longer but also of high quality and independent.
To meet this challenge, we must know much more about the nutritional needs of older persons and about how diet and nutrition influence the processes of aging.
Laying the Foundation
One hundred years ago, the U.S. Government—particularly USDA—began to lay important foundations for research on the relationships among diet, health, and aging. By establishing a USDA research laboratory at the Connecticut Experiment Station under the direction of Dr. Wilbur Atwater, with a fundamental commitment to understanding nutritional requirements, the United States also established its commitment to world leadership in research on human nutrition. Our life expectancy has increased dramatically over these 100 years, and we can increasingly use these scientific foundations to benefit older Americans.
A major impetus to research in this field came when the U.S. Congress in 1977 passed legislation establishing the USDA Human Nutrition Research Center on Aging at Tufts University. Its mission was to better understand the nutritional needs of the elderly and the relationships among diet, nutrition, and aging. In the 15 years since the program began, and in the 10 years since the opening of the research center building in Boston, substantial progress has been made toward meeting these national goals.
When the 10th edition of the Recommended Dietary Allowances was released by the National Academy of Sciences in 1989, there were numerous gaps in our knowledge about the nutritional requirements of the elderly. It is now expected that new knowledge in this area will have a substantial impact on the next edition of the Recommended Dietary Allowances.
Influence of Physiologic Change on Nutritional Needs During Aging
Some of the physical and physiological changes that occur during the aging processes are visible. The changes in skin texture, hair color, and body posture and shape are the most obvious. At the Human Nutrition Research Center on Aging, considerable attention has focused on the physiological changes that occur during aging. This will lead to better understanding of how these changes can influence our nutritional requirements, and also how diet and nutrition may influence or modify these changing functions.
The results are exciting and encouraging. The more we learn about the relationships between physiologic change and diet, and about the relationships between degenerative processes associated with aging and diet, the more we are provided with opportunities to use dietary means to slow some of these degenerative processes. These processes were once considered to be inevitably associated with aging.
Some of the physiologic differences that occur during aging and that influence requirements for nutrients are
- Changes in body composition that may result in changes in requirements for calories,
- Changes in the skin that may influence requirements for vitamin D, and
- Changes in the intestinal tract that may influence requirements for some vitamins.
Emerging research on the relationship between diet and chronic degenerative diseases of older persons holds promise for the use of diet and nutrition to treat conditions such as cataract of the eye, retinal degeneration leading to blindness, declining immune function, cardiovascular disease, stroke, osteoporosis, and even cancer. Although some of these findings, described below, are preliminary, overall they hold great promise of leading to effective programs for the health and well-being of aging and older Americans.
Changes in Body Composition
The most dramatic physiological transformation that occurs over the decades of aging is the change of the composition of the body. As lean or muscle mass decreases, along with decreasing mass and mineralization of hone, fat increases as a percentage of body weight.
These changes can result in weaker bodies; less mobility; and some risks associated with excessive body fat, including diabetes and heart disease. Research in the last 10 years emphasized that these changes in body composition are not simply changes that are programmed to occur with aging: in fact, these changes largely reflect our habits. That is to say, an increasingly sedentary lifestyle leads to the loss of muscle mass and to an increase in fat.
An important finding of current research is that at an advanced age (even 90 and above), the appropriate forms of physical exercise and activity can reverse these changes and can result in higher percentages of lean body mass and substantially increased muscle strength. This is particularly important with respect to energy requirements with aging, because caloric needs are so closely linked to the amount of lean, metabolizing muscle mass in the body. By exercising and increasing such muscle mass, we overcome one of the important changes often associated with aging: decreased appetite. A person who is becoming more active responds with increasing appetite to meet the needs of a larger lean mass and more activity. An additional benefit of physical activity is the maintenance and even increase of bone mass.
Osteoporosis is a condition that affects mostly women beyond menopause but also men to a lesser degree. The weakening of bones in osteoporosis leads to increased risk of fracture. This important health problem relates to requirements for calcium and vitamin D, the vitamin most responsible for controlling the absorption of calcium from the diet.
Much of the natural vitamin D comes from synthesis in the skin in the presence of sunlight. Because the efficiency of this process diminishes with age, the older person increasingly depends on diet for enough vitamin D to maintain the absorption of sufficient calcium. Because these needs are not usually met by diet, the blood levels of vitamin D decline with age; with this decline, the efficiency of calcium absorption also decreases. This in turn leads to the loss of calcium from the skeleton and to osteoporosis.
Recent research indicates that by increasing the dietary intake of vitamin D, we can prevent some of the age-related decline in bone minerals. We are faced with the challenge of how to best meet the increased dietary requirements of vitamin D in older persons in order to prevent osteoporosis and bone fracture.
Another physiologic change that occurs with aging that influences nutritional requirements is changes in the stomach that result in decreased production of stomach acid. Stomach acid is important for certain digestive processes including the normal absorption of dietary vitamin B12, folic acid, and iron. Partly as a result of these changes in the stomach, a higher incidence of vitamin B12 deficiency occurs in older persons. This deficiency may be important with respect to blood formation, neurologic function, and cardiovascular function. Once again, this research may allow us to better meet the increased nutritional requirements of the elderly so as to prevent the degenerative processes related to subtle dietary deficiency.
Degenerative Conditions That May Respond to Dietary and Nutritional Modification
A better understanding of the requirements of the elderly for vitamin B12 and folic acid may lead, surprisingly, to better dietary prevention of heart disease and stroke. We have heard much about the relationship between fat and cholesterol and the risk of heart disease. This knowledge has influenced the national policy on diet in a positive way. Research findings indicate that we can further control heart disease by nutritional means. Recent research shows that the amino acid homocysteine, like blood cholesterol, is a factor that contributes to the risk of coronary disease. And the blood level of homocysteine is controlled in humans to a large extent by vitamin B12, vitamin B6, and folic acid. Continuing research along these lines may provide us with other dietary means of lessening the risk of cardiovascular disease and stroke, and possibly even some of the dementing syndromes (reduced ability to reason) of the elderly.
Nutrients May Help Prevent Cataracts
The most common operation performed on older Americans is cataract extraction. Cataracts have a huge impact on the quality of life of older Americans. As we learn more about cataract formation, we better understand the interplay between antioxidant nutrients (such as vitamin C, vitamin E, and the carotenes) and the processes that damage the eye lens and lead to cataracts. Intervention studies now under way are expected to indicate the amounts of these antioxidant nutrients in our diets that may retard the onset of cataracts. Similar but much more preliminary studies relate antioxidant nutrients with senile degeneration of the retina, the leading cause of blindness in the elderly.
Like the lean body mass, the mass and function of the body’s immune system decline with age. This is extremely important because the immune system is critical in the body’s defense against infection, cancer, and other conditions. Promising research findings indicate that some of the decline in immune function associated with aging can be changed or reversed by increasing the intake of nutrients such as vitamin B6, zinc, and vitamin E. Some of this research may lead to a better understanding of how these and some other nutrients (including antioxidant nutrients) in our diet may help to prevent certain forms of cancer.
Building on Our Research
These are a few examples of the accumulating research findings that are providing the scientific basis for reconsidering some of the nutritional requirements and dietary goals for the elderly. Scientifically based programs to influence the dietary and physical activities of aging Americans can have an enormously positive impact on their health, well-being, independence, and quality of life. USDA research over the last 100 years appears to be providing a rich harvest in this area.
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