Can We Learn To Beat The Reaper?

By Jeffrey Kluger

Give the human body half a chance and before you know it, it tries to die. If it's not cancer, it's heart disease; if it's not heart disease, it's stroke. With all the ways the body can do itself in, you would almost think it wanted to end it all. The fact is, it does.

Before earthly organisms even got a chance to live, they had to agree to some pretty punishing terms: you're born, you grow up, you produce some young, then you get out of the way and leave room for the generation coming along. Animals and plants have no trouble honoring the deal; humans, however, keep trying to change it, hoping to hang around longer than nature envisioned--or our bodies can manage. For scientists and physicians, there has been no goal more seductive than extending human life, and none that has been harder to achieve. Only now are we learning that it is a goal that may forever be out of our reach.

For a long time, many scientists believed that the human life-span was infinitely extendible. The average life-span early in the evolution of Homo sapiens is thought to have been just 20 years. By the beginning of the 20th century, that figure more than doubled--to a still brief 47. Since then, however, life expectancy has been exploding, with people in the developed world now able to live deep into their 70s and often beyond.

But life expectancy (the number of years you can expect to live before being claimed by illness or accident) is not life-span (the maximum age to which the perfectly maintained, disease-free body could remain alive before it simply wore out and broke down). All the gains in length of life have been achieved by treating diseases that used to kill us in youth or, at best, in what we now consider our middle years--and are thus gains in life expectancy. Meanwhile, life-span has remained fixed at a hard ceiling of about 125 years.

"If science cured every known disease of the elderly, you'd add only 15 years to current life expectancy," says Dr. Leonard Hayflick, professor of anatomy at the University of California, San Francisco, and author of How and Why We Age. Accidents and age-related loss of organ function would then start claiming the old--though some, at least in theory, would reach the 125-year mark.

But many people continue to believe that life-spans can be pushed further still. If the aged body breaks down, it must be because something in the cells directs it to do that, and if that thing could be found and shut off, couldn't we live indefinitely? The short answer is yes. The long answer is that the short answer is way too simple.

Even before the human genome was mapped, scientists found genes that appeared to play a role in how cells age. More significantly, they discovered a cufflike structure--dubbed a telomere--at the end of chromosomes that shortens each time a cell divides. When the telomere all but disappears, the cell stops dividing, and the cell line dies out. A naturally occurring enzyme, called telomerase, can maintain telomere length in some cells.

But things aren't as easy as simply dosing a cell with telomerase. Once you immortalize the cell, it will start to divide indefinitely--just the thing cancer cells do to such destructive effect. In a recent, unrelated study that hints at the problem, scientists found that an enzyme known as P53 that has the power to suppress tumors may also shorten life expectancy. As for genetic manipulation, it is theoretically possible to re-engineer senescence genes or introduce proteins that block their operation, but with what could be thousands of genes involved in aging, that may be as far beyond biologists as building a starship is beyond rocket scientists. "That would be a long way off," admits Robert Butler, head of the International Longevity Center in New York City.

Other purported life extenders have problems too. Taking such putative anti-aging nostrums as human growth hormone or DHEA--a hormone precursor--may increase the risk of certain diseases. Restricting caloric intake by as much as 30% has lengthened life in some caged animals. But caged animals are not feral humans, and who among the already healthy is going to slash food intake by a third anyway?

The quieter news is that while immortality is beyond us, that 125-year life-span is still out there beckoning. Eliminating the dietary and lifestyle habits that are setting you up for the heart attack that is going to kill you at 50 can, in a blink, extend your life by decades. Doing the same thing on a global level--and throwing in progress on disease treatment too--can cause the life expectancy of the entire species to inch further and further out. There are about 50,000 centenarians in the U.S.--a blip in a country of close to 300 million people. But over time, those tens of thousands could creep into the millions. It takes work to join their ranks, but it is work more and more people may be willing to do.