SINCE 1900, the life expectancy of Americans has jumped to just shy of 80 from 47 years. This surge comes mostly from improved hygiene and nutrition, but also from new discoveries and interventions: everything from antibiotics and heart bypass surgery to cancer drugs that target and neutralize the impact of specific genetic mutations.

Now scientists studying the intricacies of DNA and other molecular bio-dynamics may be poised to offer even more dramatic boosts to longevity. This comes not from setting out explicitly to conquer aging, which remains controversial in mainstream science, but from researchers developing new drugs and therapies for such maladies of growing old as heart disease and diabetes.

“Aging is the major risk factor for most diseases,” says Felipe Sierra, director of the Division of Aging Biology at the National Institute on Aging. “The National Institutes of Health fund research into understanding the diseases of aging, not life extension, though this could be a side effect.”

How many years might be added to a life? A few longevity enthusiasts suggest a possible increase of decades. Most others believe in more modest gains. And when will they come? Are we a decade away? Twenty years? Fifty years?