ARE HUMANS NEAR THE END OF AGING?; SCIENTISTS WORK TO UNLOCK MYSTERY OF HOW LONG, HOW WELL WE CAN LIVE.

Byline: Bob LaMendola Knight-Ridder Tribune News Wire

Galapagos tortoises can live to be 152 years old. Could we?

The short answer is: no.

The long answer is: A growing number of scientists doubt the long-held belief that humans have a genetically programmed ``maximum age'' of 120 to 125.

They say there may be no limit to our life span. With healthier living and a few medical advances, we may be able to push the boundaries.

At the least, living to 85 or 90 soon should become routine, and many more of us will reach the century mark - without years of debilitating illness.

``A lot of people always said, `Who'd want to live to be 100?' Well, if you're healthy and active, you'd want to,'' says Ken Manton, a Duke University demographer.

Manton says he tries to practice what he preaches, adhering to a better diet and exercising more. ``I'm like everyone else,'' he says. ``I want to live a long time.''

The single best way to live longer is to inherit good genes. Short of that, human ingenuity has helped.

Our average age has climbed from 47 in 1900 to 76 today, thanks to healthier living and better medicine, vaccines and sanitation, which have wiped out killer infectious diseases.

The ranks of the elderly are climbing rapidly. About 60,000 people topped age 100 last year. Four million beat 85, almost double that of 1980.

By 2020, the U.S. Census Bureau expects 214,000 centenarians and 7 million to 8 million people over 85. One in nine Baby Boomers may live a century. At the end of World War II, only one in 500 made it.

Dodging life's pitfalls

Picture your life span as a road riddled with potholes. Dodge one and your life span ticks up.

As kids, the threats are infant diseases, accidents and parents who kill. Young adults succumb most to accidents and infectious disease (led by AIDS). Middle-agers must beat heart disease and cancer, twin killers that decimate those in their 60s and 70s.

But make it to 75, and chances are good you will see 86. Reach 80, you'll live another eight years on average.

Overall, however, some scientists believe none of us will ever approach the tortoises. They contend we can live only so long, that our cells are programmed to die after a given time. In this view, the average age tops out at about 85. The healthiest of us would hit a ``brick wall'' at about 120.

Thing is, the wall keeps moving, according to researchers who doubt the theory.

It was in 1800 that a person was first confirmed to be 100. (Tales of ancient Russians living to 120 have never been proved.) Proof of the first to reach 110 came in the 1930s; the first to reach 120, in 1986. This year, a French woman died at a confirmed age of 122.

The increase in maximum age and average age has been accelerating.

From his studies, Ronald Lee, head of demography at the University of California at Berkeley, predicts a slow and steady increase in longevity. By 2065, he expects the average age to be 86.

Some scientists believe we can extend longevity to the mid-90s simply by living right - no smoking, a low-fat diet, plenty of exercise.

``It's not extreme behavior that does it,'' Duke's Manton says. ``It's not running a marathon. It's going out walking four or five times a week; it's eating a sensible diet with limited fat.''

Manton is not naive enough to think people will suddenly change their ways. But he and others say generations reaching old age in the next few decades are better educated. They know more about living healthy, are more interested in it and are more willing to try.

``There's tremendous capacity for advances even if there are no more medical breakthroughs,'' says demographer Sam Preston of the University of Pennsylvania. ``And you know there will be some of those.''

Medical advances

In the early 1900s, longevity jumped as antibiotics beat killers such as diphtheria. People lived long enough to die from heart attacks and cancer.

Now we're making headway against the chronic diseases, sometimes with new uses for old remedies.

Humble aspirin turns out to be a heart-attack preventer. Ibuprofen may ease Alzheimer's disease. Most ulcers, we now know, are caused by a bacteria that is easily killed.

There's tremendous promise in the emerging field of genetics.

Almost daily, researchers find another cause for disease and death within our 100,000 genes. Because genes are the inherited instructions for replacing cells, one mutation may have a big impact.

Researchers believe dozens, if not hundreds of genes control longevity. Ultimately, they hope to learn to manipulate the process and lengthen life.

``We're getting to a takeoff point where these technologies are going to start bearing fruit,'' Manton says.

It was while tinkering with yeast last year that researchers challenged the notion of a ``brick wall'' maximum age. By tweaking a gene called LAG-1, they got the yeast cell to reproduce 28 times before halting. Normally, the maximum is 21.

Human cells have a similar cellular clock. No one knows exactly how the clock works. But the yeast experiment suggests it can be manipulated.

Scientists also are studying compounds that damage cells and shorten our lives. The leading culprit: free radicals. Every health-food store today pushes antioxidants to combat this evil horde.

The normal act of burning food produces free radicals, which are oxygen molecules with an unmatched (free) electron. So desperately does the cell want a mate, it grabs an electron from another cell, causing instability. Free radicals are linked to cancer, genetic damage, hardened arteries and more. Pollution and smoking also spawn them.

``Aging is a biological disordering. As we get older, we go from an ordered state to a disordered state,'' says George Roth, a physiologist at the National Institute on Aging.

Antioxidants such as vitamins E and A and beta carotene come to the rescue. They pair with the free radical, reducing damage. Doctors say, however, that taking supplements does not work as well as getting antioxidants through the diet.

Eat less, exercise more

For now, the best advice from the experts is painfully familiar: Eat more fruits and vegetables, less fat. And don't forget to exercise.

Exercise is emerging as an elixir in all of this. Even people over 90 benefit from simple walking or weightlifting. They have more muscle, strength and mobility.

``Not only will you live longer, you'll be living with fewer health problems and infirmities,'' Manton says.

Along the same line, a theory called caloric reduction says you live longer by eating noticeably less. It works in animals.

Burning food wears down the body's machinery and creates free radicals and other byproducts. Less food, in this view, causes less harm.

Researchers have noticed for 60 years that lab animals fed 30 percent less than normal - while still being given full nutrients - live 30 percent longer.

Federal researchers in Baltimore now are testing the theory on 200 rhesus monkeys. So far, the results are ``very encouraging,'' says Roth, who heads the study.

The monkeys matured about a year later than normal, were lighter and smaller, had much less fat and only a little less muscle, Roth says. They show improved levels of free radicals, stress compounds and blood sugar. Their metabolisms seem to have shifted from a growth strategy to a more efficient maintenance strategy.

No one knows if the practice works for humans; Roth warns against trying it without a doctor's care. Still, some devotees of the theory already have started cutting chow by a third.

``There probably is an application to humans,'' Roth says, ``(but) we don't know enough about side effects yet to do anything.''

But his goal is not making people eat less, it's learning cell mechanics and finding a drug that lets us eat normally without the damage. He says he wouldn't want to eat less himself and has not cut back much.

``People love to eat; it's a big part of their lives,'' Roth says. ``The monkeys are perfectly healthy and we think they will live longer, but they are hungry a lot.''

Buying more time

So what can we do today to live longer? Some tips for sidestepping the land mines:

Stop smoking - Quitting for five years adds two years to the average life expectancy.

Exercise: 90 minutes a day for more than three years adds three years; 20 minutes a day for that long adds one year.

Reduce blood pressure: Below 120/80 adds three years.

Cut fat: If less than 20 percent of total calories, adds two years.

Reduce bad cholesterol: Below 160 adds a year.

Boost good cholesterol: Above 55 adds a year.

Prevent diabetes: Adult onset diabetes cuts a year.

Eat fruit and veggies: Five servings a day adds one year.

Mate well: A happy marriage adds two years for a man, one for a woman.

Socialize: Seeing three social groups once a month adds two years.

Use seat belts and child car seats.

Protect kids: Immunize, eliminate household hazards, teach swimming, avoid gangs.

Practice safe sex.

Drink in moderation.

Get tested: Between 40 and 65, begin routine tests for prostate, breast and colon cancer.

Knight-Ridder Tribune News Wire

CAPTION(S):

2 Photos, Box

Photo: (1--Cover--Color) This tortoise can live to 152. Could we?

Michael Owen Baker/Daily News

(2) Is there a limit to age? Researchers say there probably is, but that humans can prolong their lives well into what is now considered old age by eating right, exercising and taking advantage of modern medical breakthroughs.

Box: Buying more time (See Text)