| One major practical achievement is the opportunity to develop better standards of normality. In the glucose tolerance test for diabetes, for example, after the subject drinks the glucose (sugar) solution or has it injected in his vein, the glucose level in the blood is checked by taking blood samples at intervals over a two-hour period. The level that doctors have for years assumed to be "normal" is the normal level for young, healthy adults in their twenties. But the NIA GRC studies show that this standard is inaccurate when applied to older people. By this standard of normality, up to half the older subjects would be mis-classified as diabetics. So an adjustment must be made for age, and Center investigators have devised a way to make this adjustment. |
 In the longitudinal study my ability to metabolize glucose (sugar) is measured over many years to see how it changes with age. The sugar solution is either injected in a vein, or I must drink about a pint of it. The volunteers' joke about World War II "battery acid" drinks made from instant powders get a little stale, but there's a late breakfast to look forward to, usually about 30 minutes before lunch time. During the two-hour test, blood samples are collected periodically through a vein catheter in my arm. |
| NIA GRC research has also laid to rest the theory that there is an adult plateau period for most physiological functions. It is not true that the individual reaching maturity achieves a long period of stability and then, suddenly, begins to slide downhill faster and faster with age. Most changes are gradual and progressive. In the area of reasoning and logical problem-solving, for example, Dr. David Arenberg and his associates have demonstrated a decline in performance by older men, but only for those subjects who were over 70 when first tested. Comparisons of performance of young and old men in the volunteer group show that the proportion who successfully solved each problem decreased with age, even in a group of highly educated men. Older persons, when confronted with problem-solving situations, tend to be less able to try new approaches, repeating instead the same approach. On the other hand, many older subjects, especially those first tested while in their sixties, showed no decline in performance on retesting. |  This one is fun! It's a problem-solving "game." My task is to determine the relationships between ten lights on the display board and to use that knowledge to turn on the center "goal" light. Changing the rules after each problem is solved makes it more challenging. Using this test, scientists have observed that the ability to solve reasoning problems declines in late life. |
| In the glucose tolerance tests, NIA GRC scientists do find a plateau. They note a loss in the ability to handle glucose as the individual moves from his twenties into his forties. And finally, in later years, a decline sets in again. There are, however, some important exceptions to this principle. The patterns of age decline in the various diagnostic tests for diabetes differ. In the commonly used oral glucose tolerance test, the usual pattern of progressive decline occurs. But when the glucose is injected into a vein there is actually a more rapid age decline in the early adult years than in the middle years of life. |
| Cholesterol studies show an increasing amount in the blood up to age 55, then a decrease. Thus, high levels of cholesterol in the blood -- a possible risk factor in heart disease -- peak at about age 55. Cholesterol in the blood shows still another age pattern, with a gradual increase in level during the early adult years, then a plateau period, and finally a decline in older years. The role of changes in body composition (obesity, for example), dietary habits, and patterns of activity in this important variable are under investigation. |
| Despite the importance of alcohol from a social, behavioral, medical, and legal standpoint, there has been no investigation of the relationship aging might have on the way it is metabolized by the body, until NIA GRC scientists studied its effects. NIA GRC researchers made the rather surprising discovery that alcohol is metabolized just as efficiently in the aged as in young adults. But, at the same blood levels, the older men had greater declines in intellectual functions such as memory and decision-making tasks, as well as in reaction time. |
| A new echocardiography technique which measures heart size and performance shows a significant increase in the diastolic (or relaxation phase) blood pressure in the aorta of older men -- a 10 to 15 percent increase from age 30 to age 80. In addition, the wall of the left ventricle of the heart shows a 25 percent increase in thickness over the same period. And the speed with which the mitral valve (which controls blood flow in and out of the heart) opens and closes decreases by 5 percent, perhaps reflecting the slower filling of the stiffer, thicker heart ventricle in later years. The size of the heart cavity, the extent of shortening of contractile fibers, and the speed of that shortening do not change much with age. |
| Longitudinal subjects in Baltimore have also participated in a study of cellular aging outside the body -- that is, in test tubes. Small pieces of skin were taken from the upper arms of the volunteers and were used to develop skin tissue cultures. NIA GRC researchers find that the cells in these small pieces of skin will actually undergo growth and cell division in cultures. This opens broad new areas of study since human cells from different aged donors can now be studied under carefully controlled experimental conditions. NIA GRC finds that cells from older donors undergo a smaller number of generations of cell division before losing their ability to reproduce. Age differences have also been noted in the structural and chemical characteristics of the cells in culture. |
| Promising results may come from NIA GRC studies of so-called hormone receptors (which may be thought of as tiny receiving sets) and their role in the aging process. Medical scientists have known for a long time that hormones, circulating in the blood stream, send signs to body cells which call for certain functions, such as metabolism of fats or to help the body in adapting to stress. They have known too that these signals are received from the hormones by small protein receptors located either outside or inside the cells. The Baltimore researchers find that the receptors definitely change with age, decreasing in number in both humans and animals. They conclude that the loss of receptors may be an important factor in the aging process. Currently they are trying to learn more about the way in which the receptors are lost and to determine if certain chemicals can reverse the trend. If ways can be found to restore the numbers of receptors in old cells, the practical benefits for older people would be enormous. |
| Separate studies of daydreams and sexual activity conducted by NIA GRC researchers Dr. Leonard M. Giambra and Dr. Clyde E. Martin add important new understanding of sexuality among older people. |
| Dr. Martin's research shows a high degree of correlation with previous studies in this field which told us that frequency of sexual activity steadily declines over most years of the male life span. But Dr. Martin also finds that males tend to maintain comparatively high or low levels of sexual activity throughout their lives. Frequency in early marriage and in the 20- to 40-year age period, corresponds significantly with sexual frequency after age 40. Dr. Martin also correlated these studies with such tests as maximum breathing capacity, basal metabolic rate, cholesterol level, and oxygen consumption and concluded that physical well-being (as measured in these terms) is an important factor in determining sexual responsiveness and activity after age 65. |
| Dr. Giambra found that the frequency and intensity of sexual daydreams show a direct relationship to age, decreasing in older subjects. In a joint analysis of their separate studies, Drs. Martin and Giambra conclude that greater sexual activity or vigor and greater frequency or intensity of sexual daydreams are directly related and that these findings are consistent across the male adult life span. |
| To sum up, NIA GRC studies show a large variation in how individuals age. In observing a group of persons in their seventies, it is obvious that some are physically vigorous, mentally alert, and happy with their position in life. Others seem to slow down at much earlier ages. It is possible now to document some of these changes. |
This one is hard work even though I'm lying down. I'm cranking a bicycle "ergometer" to determine the effects of aging on the maximum "arm work output" I can muster. The muscle strength of arms and shoulders declines less on the simpler task of pulling or pushing a stationary object than does the overall ability to use the muscles in a coordinated movement such as turning this crank. The decline begins at about age 45. I was almost that young when I started these tests 20 years ago.
The new technique of echocardiography permits studies and measurements of my heart size and performance. The "nozzle" through which the ultra-sound waves (two million cycles per second) are sent into my chest is cold to the touch, but, as the doctors tell me, it's "noninvasive" which means that no needles or vein catheters puncture my skin. The sound waves reflect off the various parts of my heart, sending echoes to the receiver at upper right which transforms them into a line picture. These echoes show variations as small as one millimeter in the movement of my heart.
This sound-proof chamber is about the same size as the one we have seen on TV, but there's no $64,000 at stake. Tones of varying pitches and duration are piped into my earphones. I indicate my hearing "thresholds" (levels at which I can no longer hear the tone) by pressing a button on the device in my left hand. My "thresholds" are plotted electronically on a graph outside the chamber.
