Aging : The Immune System, Calories and Diet

by National Institute on Aging

(Page 12 of 15)

Muscles: Without exercise, estimated muscle mass declines 22 percent for women and 23 percent for men between the ages of 30 and 70. Exercise can slow this rate of loss.

Bones: Bone mineral is lost and replaced throughout life; loss begins to outstrip replacement around age 35. This loss accelerates in women at menopause. Regular weight bearing exercise - walking, running, strength training - can slow bone loss.

Sight: Difficulty focusing close up may begin in the 40s; the ability to distinguish fine details may begin to decline in the 70s. From 50 on, there is increased susceptibility to glare, greater difficulty in seeing at low levels of illumination, and more difficulty in detecting moving objects.

Hearing: It becomes more difficult to hear higher frequencies with age. Even older individuals who have good hearing thresholds may experience difficulty in understanding speech, especially in situations where there is background noise. Hearing declines more quickly in men than in women.

Personalit: Personality is extraordinarily stable throughout adulthood. Generally, it does not change radically, even in the face of major events in life such as retirement, job loss, or death of loved ones. However, there are exceptions. Certain individuals facing these and other lifealtering circumstances can and do show signs of personality change during the final years of life. An easy-going individual who loses a job after many years, for instance, may become disillusioned and develop a sullen disposition. But these out-of-character reversals of personality are relatively rare.

The Immune System

When Shigechiyo Izumi of Japan contracted pneumonia and died in 1986 at the reputed age of 120, it was his immune system that failed. One of the many bacteria or viruses that cause pneumonia broke through the elaborate, natural defenses that protect humans from infection. Scientists have long known that these defenses decline with age; now, some of the underlying mechanisms are coming to light.

A multiplicity of cells, substances, and organs make up the immune system. The thymus, spleen, tonsils, bone marrow, and lymphatic system, for example, produce, store, and transport a host of cells and substances - B-lymphocytes and T-lymphocytes, antibodies, interleukins, and interferon, to name a few. Several are of special interest to gerontologists. These include the class of white blood cells called lymphocytes, which fight invading bacteria and other foreign cells.

Lymphocytes fall into two major classes: B-cells and T-cells. B-cells mature in the bone marrow, and one of their functions is to secrete antibodies in response to infectious agents or antigens. T-cells develop in the thymus, which shrinks in size as people age; they are divided into cytotoxic T-cells and helper T-cells. Cytotoxic T-cells attack infected or damaged cells directly. Helper T-cells produce powerful chemicals, called lymphokines, that mobilize other immune system substances and cells.

T-cells and their lymphokine products have intrigued gerontologists ever since it was learned that T-cells - or more precisely the functioning population of T-cells - declines with age. While the number of T-cells remains about the same, the proportion of them that proliferate and function declines. Studies have also shown that in older people, T-cells destroyed by stresses such as irradiation or cancer chemotherapy take longer to renew than they do in younger people.

Most research on the aging immune system now centers on these cells. One group of T-cell products, interleukins, is found at different levels as people age. The interleukins - there are more than 20 identified so far - serve as messengers, relaying signals that regulate the immune response. Some, like interleukin-6, rise with age, and it is speculated that they interfere in some way with the immune response. Others, like interleukin-2, which stimulates T-cell proliferation, tend to fall with age. Gerontologists study the interleukins, not only for clues to the mechanisms of aging, but also for their potential in the detection and treatment of immune problems.

Meanwhile, compelling evidence suggests one intervention - caloric restriction - may counteract some of the natural declines in the immune system as well as in other physiological systems of aging animals.

Caloric Restriction

An inventor, statesman, diplomat, and scientist, Benjamin Franklin was a true Renaissance man renowned for his sage advice. Among his many pearls of wisdom: "To lengthen thy life, lessen thy meals." Nearly 275 years later, gerontologists are finding those words may turn out to be amazingly prophetic.

Since the 1930s, investigators have consistently found that laboratory rats and mice live up to 40 percent longer than usual when fed a diet that has at least 30 percent fewer calories than they would normally consume. The animals that eat this nutritionally balanced diet, which provides healthful amounts of protein, fat, and vitamins and minerals, also appear to be more resistant to age-related diseases. In fact, caloric restriction appears to delay normal age-related degeneration of almost all physiological systems. And so far, caloric restriction has increased the lifespans of nearly every animal species studied including protozoa, fruit flies, mice, and other laboratory animals. Now investigators are exploring whether and how caloric restriction will affect aging in monkeys and other nonhuman primates, our closest relatives in the animal kingdom.

About the Author

www.nia.nih.gov
NIA, one of the 27 Institutes and Centers of NIH, leads a broad scientific effort to understand the nature of aging and to extend the healthy, active years of life. In 1974, Congress granted authority to form NIA to provide leadership in aging research, training, health information dissemination, and other programs relevant to aging and older people.