It's never too late ... to change lifestyle habits, that is.

During the past century, dramatic improvements in life expectancy have been achieved in many countries worldwide. In the United States, for example, life expectancy (or the number of years a newborn baby can expect to live) has increased from 47 to nearly 76 years during the 1990s, and is expected to exceed 82 years by the year 2050.

In simple terms, the baby boomers are getting old, a phenomenon many experts call the "age wave." In fact, the fastest-growing minority in the United States is the "very old" (the 85-and-older population), a group that is projected to expand from 3.1 million in 1990 to approximately 17.7 million by the year 2050.

But the central issue is how are we aging? The National Center for Health Statistics has estimated that 15 percent of the average American's life is spent in an "unhealthy" state (that is, impaired by disease, disabilities, and/or injuries). Among those reaching age 65, five of their remaining 17 to 18 years, on average, will be unhealthy ones.

Health habits have a strong influence on both life expectancy and quality of life during old age. Dr. Lester Breslow of the UCLA School of Public Health, in his famous study of more than 6,000 people in the San Francisco Bay Area, showed a dramatic difference in death rate between those who followed seven simple health habits (never smoked, moderate or no alcohol consumption, daily breakfast, no snacking, seven to eight hours of sleep per night, regular exercise, ideal weight) and those who did not. Those following all seven health habits were estimated to live nine years longer and suffer less disability than those who did not practice any of them. In other words, healthful living appears not only to promote longevity but also to increase the chance of having the physical ability to enjoy life to its fullest in later years. Dr. Breslow urges that "establishing healthful habits early in life is particularly beneficial," but that "evidence is growing that it's never too late to change."

Exercise and aging. A key ingredient to healthy aging, according to many who study aging, is regular physical activity. Of all age groups, the elderly have the most to gain by being active, including the potential for decreased risk of heart disease, cancer, high blood pressure, depression, bone fractures, and diabetes, with improved body composition, fitness, longevity, ability to perform personal care activities, and management of arthritis. Yet national surveys indicate that only about one third of the elderly exercise regularly, which is less than any other age group.

Interestingly, many of the changes that accompany aging are similar to those experienced during prolonged bed rest, inactivity, and weightlessness. These changes include a decrease in heart and lung function, and muscle and bone strength, with a gain in body fat. Many researchers who have evaluated the effects of aging on the body have focused on [VO.sub.2] maximum, or the ability of the body to take in oxygen, transport it, and use it for burning fuel to supply energy for activity. [VO.sub.2] max is seen by many as the single best variable to define the overall changes in the body that occur with aging.

[VO.sub.2] max normally declines 8 to 10 percent per decade for both males and females after 25 years of age. At any given age, people can have a much higher [VO.sub.2] max if they exercise regularly and vigorously.

Amazing Mavis. Called "Amazing Mavis" by Sports Illustrated and many of her admirers, Mavis Lindgren is a living example of the benefits that come with regular exercise even in old age. She's a true "late bloomer," having endured and overcome an unhealthy past. As a child in Canada she suffered through whooping cough and pneumonia, and experienced annual bouts of severe bronchitis throughout her adulthood. Despite her training as a nurse, she couldn't seem to keep well.

Mavis was introduced to regular exercise while attending a convention in British Columbia when she was age 62. Inspired by what she had learned about the importance of exercise for health, Mavis, 20 pounds overweight and very out of shape, decided to begin a regular walking program.

Slowly she increased her walking distance and after several weeks began adding a few jogging steps to her routine. As the months rolled by, Mavis experienced a rebirth of health. And as walking became easier, she discovered that she loved how she felt while running.

Mavis eventually found herself running four or five miles six days a week and enjoying it. She kept this up for several years, and to her delight, the annual bouts of bronchitis and pneumonia did not return, and she slimmed down.

In 1977 the running world discovered Mavis, then 70, thanks in great part to the persuasiveness of her son, a physician who realized her unusual potential and urged her to double her training for marathon running. She began running 40 to 50 miles a week, a training regimen she still follows. Mavis found that she enjoyed the challenge of marathon running, and between 1977 and 1994 she raced in 65 marathons, resetting her own age group world record four different times (her age group world record was 4 hours 34 minutes). Mavis also became the oldest woman ever to run the race to the top of Pike's Peak in Colorado. In the fall of 1993 she was the oldest female finisher of the New York City Marathon, at age 86.

I have been studying Mavis for the past decade, measuring her heart and lung function. Between the ages of 77 and 80, her [VO.sub.2] max averaged an aerobic power equal to that of untrained women in their 20s. Despite some decrease since age 77, Mavis still enjoys the [VO.sub.2] max of a woman about half her age. She has demonstrated that it's never too late to start exercising.

Mavis is still running marathons, with no end in sight. "As long as my legs hold out, as long as I can continue to inspire others, I'll keep running. Besides, if I stop now, old age might catch up with me!"

How much exercise is enough? Although Mavis likes to run and train for marathons, this amount of exercise is not necessary for basic health benefits.

We're urged to accumulate 30 minutes or more of moderate-intensity physical activity over the course of most days of the week. Activities that can contribute to the 30-minute total include walking up stairs, gardening, raking leaves, walking, swimming, and cycling. One specific way to meet the standard is to walk two miles briskly each day, a program that most elderly persons can engage in successfully and reap health benefits.

"Many elderly people wouldn't need so much medication, and fewer would end up in rest homes, if they would just walk every day and simplify their diets," says Mavis. "Look at me--I'm a case in point. In middle age I was sickly and weak, but in my old age I'm healthy and strong. It's wonderful to wake up each morning at age 87 and not hurt anywhere!"