Treating some of the underlying diseases of aging, such as heart disease, cancer or Alzheimer's disease could slow down or delay aging by 20 or 30 years, say medical researchers.

Some of these drugs have already pushed the lifespans and "healthspans" of laboratory animals. Now the trick is getting them to work in people.

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"We have a dozen ways to make mice live 20 percent longer than they do now," said Stephen Austad, professor of biology at University of Alabama at Birmingham. "That's a huge shocker. But given the number of ways that work in animals, I'm quite confident that some will extend to people. We are likely to see a quantum leap."

Austad and colleagues are preparing to launch a clinical trial of a diabetes drug called metformin that has the side effects of keeping patients free from the diseases of aging.

"Nobody will have a trail where you give something to a bunch of 20 years olds and wait until they die," said Austad. "What will happen is we will start using older people. The only way to demonstrate that something works like this is take a group of people at sufficient risk of death that you will be able to see a difference."

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Austad and others are currently looking for 70 candidates for the first five-year trial. Metformin effects three metabolic pathways in the body responsible for aging. Diabetic patients who took the drug lived longer than healthy patients who did not, according to Austad. Because its already been approved for use by federal officials, Austad and his team won't have to go through lengthy pre-clinical tests for safety.

At the same time, other researchers are working on several other strategies to combat aging. Another drug is rapamycin, which inhibits cellular processes during cell metabolism.

"When you give it to a variety of animals, they all live longer and healthier," said Nir Barzilai, professor of medicine and genetics at the Albert Einstein College of Medicine.

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"If we give mice a combination of rapamycin and metformin, their lifespan is increased 25 percent," Barzilai said. "For humans it's a lifespan of 100 years instead of 75 years. This is the most promising approach."

But there's a catch. Rapamycin has nasty side effects, such as cataracts, testicular atrophy and maybe diabetes. "This drug needs better development," Barzilai said.

There's also acarbose, another diabetes drug that stops the breakdown of sugars in the intestine, and has shown to have age-delaying effects. He's leading a small trial in Singapore, where the drug is more commonly used.

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Both researchers say that medical breakthroughs in the next decade will allow doctors to better prescribe these drugs. One possible first use is to help elderly patients have a better immune system when they have to go in for surgery.

Will living longer change us? Austad says the implications of living another 25 years could be immense.

"That will influence when we have kids, what kind of careers we have, and our second, third or fourth careers," he said. "The trajectory of life that we have developed over last century, that might change considerably. It might be that people suddenly decide I want to do x, or that it's time for me to go back to school and do something else. I think it has potential to change more things than we realize."