However, researchers who study aging stress that getting old and getting sick are two different things. People differ considerably in the way they age. There is a difference, say researchers, between chronological age and biological age. (See the box “What Is Aging?”) In other words, getting older and going downhill do not necessarily go together.

WHAT IS AGING?

“The biological crystal ball is very cloudy when we come to aging,” says one researcher. “No one fully understands it,” states another. Even so, gerontologists (scientists who study aging) have attempted to define it. Simply put, they say, aging is the chronological time that someone has existed. But aging is more than the passing of years. One does not normally speak of an aging child because aging has a connotation of deterioration of vitality. Aging is the toll that the passing years take on an individual. Some people seem young for their chronological age. This is implied, for example, when an individual is told that he doesn’t “look his age.” To distinguish between chronological and biological aging, researchers usually describe biological aging (aging accompanied by harmful physical changes) as senescence.

Professor of zoology Steven N. Austad describes senescence as “the progressive deterioration of virtually every bodily function over time.” And Dr. Richard L. Sprott, of the National Institute on Aging, says that aging “is the slow deterioration of those portions of our systems that allow us to respond adequately to stresses.” Most experts agree, though, that coming up with a clear definition of aging remains a challenge. Molecular biologist Dr. John Medina explains why: “From head to toe, from proteins to DNA, from birth to death, untold battalions of processes unfold to create the aging of a 60-trillion-celled human.” Small wonder that many researchers conclude that aging is “the most complex of all biological problems”!