Life Extension: Science Fact or Science Fiction?
Bill just died of a heart attack at age 67. His brother, Jim, twelve years older, still enjoys playing golf once a week. Why is Jim living so much longer? Does he take after their mother's family who all lived into their eighties? Or, does he just have a healthier lifestyle?
What makes people grow old? How can we live longer? Why do members of some families seem to live longer than others? Can people live to 150 years old? Would you want to? These questions have fascinated people for centuries. Now scientists who study aging, called gerontologists, are trying to answer them.
Genes now being studied may one day answer some of these questions. Genes might be considered little packets of information found in each cell in our bodies. These packets contain instructions that tell our bodies how to grow and work. For example, they control whether we get our grandmother's blue eyes or our father's crooked little finger. For some people genes may affect how long they live.
Areas of Research
Several "longevity genes" have been found in some living organisms. Scientists studying certain worms and fruit flies have found several genes that seem to control how long these creatures live. By making a change in just one of these genes, they have almost doubled the average lifespan of both fruit flies and one type of worm. Others looking at longevity genes have shown that the gene already shown to control how fast yeast cells age may do the same thing in mice. This gene is also present in humans. As interesting as this work is, it is unlikely that changing genes will be tried in humans in the near future as a way to help them live longer.
Genes alone, however, are only a part of the reason that some people live a long time. How people live, their lifestyle, may be more important. For example, does someone smoke? Do they exercise? Are they under a lot of stress? What do they eat? Some scientists think what people eat and how much they eat can lead to a longer life. Caloric restriction is one area of research on aging. A calorie-restricted diet has 30 to 40 percent fewer calories than a normal diet, but it has all the needed nutrients. This diet seems to extend the life of almost every animal type in which it is studied. It has worked in protozoa (very small, one-celled organisms), fruit flies, mice, and rats. Recent studies in primates, such as monkeys, are not complete. They do, however, show a slowing in some measures of the aging process in primates on this diet. Primates are our closest animal relatives. This diet has not been tested in humans. We do not know whether it will have the same life-extending effect in people. Conducting such a study in people is not practical because people would have trouble following such a diet.
How does caloric restriction work? We do not know. Some scientists think that eating fewer calories lowers body temperature and changes metabolism, the breakdown of substances so that the body can easily use them. This, in turn, lessens damage to cells and slows certain other cell-damaging activities. In fact, caloric restriction seems to slow the whole process of growing older. Animals that have been on restricted diets since their youth reach adulthood later than others not on these diets. Not only do these animals seem to live longer, they also have less illness. Although we don't know how this works in people, scientists do know the flipside-that people who are overweight are more likely to develop certain age-related diseases such as heart and blood vessel disease, high blood pressure, arthritis, cancer, and diabetes.
Is there is a link between the so-called longevity genes and our body's use of food? The single gene in fruit flies that was changed to lengthen their lifespan is related to the way that the fruit fly stores and uses energy, usually gotten from food. Other scientists studying genes in yeast cells recently found a chemical that seems to work with a longevity gene to increase the yeast cell's lifespan. This chemical is also part of the yeast cell's processing of energy.
Experts in aging do not expect ever to recommend such caloric restriction for people. But these studies will help them understand aging. They may also teach us how to prevent or delay diseases that seem to come with growing older. Understanding how caloric restriction works might also help scientists develop chemicals that could imitate its effects on the aging process.