Recent experiments on everything from roundworms to mice are giving some scientists hope that our maximum life spans are not set in stone, but can be extended far beyond what nature intended.

In many ways, tremendous progress has already been made in extending human life.

From lowering infant-mortality rates (the biggest factor) to creating effective vaccines and reducing deaths related to heart problems, science has helped the average American's life span increase by nearly three decades over the past century.

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But getting the average person from 80 to 120 and beyond requires research into the very cellular mechanisms that cause gray hair and wrinkles, that make our bones creak and our minds go weak — what generally makes all creatures shrivel, shrink and waste away.

The big question: Can cellular aging be halted or reversed?

Eat less

The first hint of the possibilities came in the 1930s, when studies by Cornell University researchers discovered that rats fed severely reduced calories tended to live up to 40 percent longer than their fully fed litter-mates.

Scientists still aren't sure how caloric restriction, or CR, works. One early hypothesis, that CR regimens extended life span by preventing animals from reaching full body size, was debunked when experiments showed that even fully grown adults can benefit from CR.

For about 50 years, CR was the only proven method to extend an organism's maximum life span in a healthy way.

Then in 1996, scientists discovered a type of mutant dwarf mouse that lived up to 70 percent longer than its non-mutated peers. The rodents' stunted growth was due to a change at the genetic level that reduced production of hormones related to growth.

Genetic tinkering

In the years since, genetic tinkering has also produced more enduring yeasts, roundworms and fruit flies.

Much of the anti-aging research is still done on rodents, whose biological systems are similar to humans in many ways. In fact, a leading proponent of human anti-aging research has organized a hefty prize for breakthroughs that extend the lives of mice.

Scientists have also discovered other factors that affect life span in research that might eventually be applied to humans. A study out of Cambridge University in England found that what a mother eats during pregnancy and while nursing can greatly affect her children's life spans.

Using mice, the researchers found that mothers fed protein-rich diets during pregnancy, but low-protein diets while breast-feeding, had pups that lived up to 50 percent longer than those for whom this feeding pattern was reversed.

If a similar approach could work for humans, this translates into a difference between reaching 50 and living to be 75 years old, the researchers said.

Get married

If the thought of eating only enough to survive or having your genes mucked with doesn't sound very appealing, scientists say there is another and perhaps more pleasurable way to live longer: Fall in love.

A study earlier this year led by Linda Waite, a sociologist at the University of Chicago, showed that happily married couples tend to live longer than unwed individuals. Married men were found to live, on average, 10 years longer than non-married men, and married women lived about four years longer than non-married woman.

The researchers speculated that married men live longer because they adopt healthier lifestyles and take fewer risks. Married woman, on the other hand, probably live longer because of the improved financial well-being that comes with marriage.

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