Each generation has searched for fountains of youth. But now science is taking up the cause that historically was the domain of the fantastical.

As a first step, researchers are working to understand the biology of aging to extend the “healthspan” of older adults people rather than emphasizing lifespan, which can involve tacking on a few extra months for the seriously ill. The research also has shown the possibility of slowing down, halting and even reversing aging of mice, worms, flies, yeast and fish through genetic manipulation, drugs and natural enzymes.

Such topics have gained importance as the result of troubling trends in American health.

“One hundred years ago, life expectancy was 46 years. In the last 100 years that has almost doubled,“ said Felipe Sierra, director of the National Institute of Aging’s Division of Aging Biology. “But if we’re going to get dramatic improvements in longevity, some things need to change.”

Right now the United States is 34th in the world with a life expectancy of 79 years, which is lower than Cuba, Lebanon and Costa Rica and more than four years behind world leader Japan, according to the World Health Organization.

Eighty percent of Americans 65 and older have at least one chronic condition — cancer, cardiovascular disease, arthritis, diabetes, dementia or Alzheimer’s disease, among others — with 50 percent having two. That means most older Americans are battling serious illnesses and disabilities throughout their senior years.

“One hundred years ago we didn’t have the luxury of old age,” said Susan Peschin, an O’Hara native serving as president and CEO of the Alliance for Aging Research in Washington, D.C. “While we have been able to add years to life, we have not been able to maintain health and vigor. The idea is to compress morbidity and lengthen the period of health and vigorous life.”

Founded in 1986, the alliance is a nonprofit organization dedicated to accelerating the pace of scientific discoveries and their application to improve the universal human experience of aging and health.

Chronic diseases among older Americans cost $1 trillion a year in the United States and could rise to $6 trillion by 2050 if health doesn’t improve in that age group, she said.

“We can speed up aging by genetics or poor lifestyle, but you also can slow it down, and scientists know some basic processes that occur in the body that lead to chronic diseases in aging, including stress response, inflammation and reductions in cell replacement and repair,” she said.

And with baby boomers entering the gates of old age in droves, there’s added incentive to figure out the mechanisms of aging to maintain better health.

Ms. Peschin said there’s evidence that preventing age-related chronic diseases represents the best way to lower health-care costs. An October 2013 Health Affairs study said it’s possible by 2030 to develop interventions to increase life expectancy at age 51 by 2.2 years and most of those added years would be spent in good health. The study also estimates that increasing the number of healthy years of life would save about $7.1 trillion by 2050.

The focus: Geroscience

Mr. Sierra of the National Institute of Aging said the big focus of what’s known as “geroscience” — understanding the relationship between aging and age-related diseases — is discovering ways to slow down the aging process and delay all chronic conditions. Treating one at a time is failing.

While the National Institutes of Health funding for aging research hasn’t increased, there’s a broader focus on the topic, with studies regularly appearing in such major journals as Nature and Cell. Science, he said, no longer views the human body like an automobile that wears out or breaks down.

Mr. Sierra said that scientists have identified a single gene that improves longevity. But since the 1930s, science has known that, in mice and rats, reducing calorie consumption over a lifetime improves longevity.

Now they have discovered that surtuins — proteins that control several biological pathways — are involved in the aging process. These proteins, present in such antioxidants as resveratrol (the ingredient in red wine), may be the means by which low calorie consumption extends longevity. The drug rapamycin also dramatically extended longevity in animal studies, prompting more research.

Researchers also have reversed the aging process in old mice through transfusions of young-mouse blood. That likely won’t occur with humans, he said, due to ethical considerations. In addition, scientists have discovered a higher concentration of the GDF11 protein in the blood of younger mice, which could represent another factor that produces anti-aging impacts on cognition, the heart, eyes and muscles.

But Mr. Sierra said a pill to forestall aging is futuristic with a definite downside should it convince people to abandon a healthy lifestyle.

“The last thing I want, but can’t control, is for people eating like pigs and watching TV to pop a pill and think they are healthy,” he said.

Realities of aging

Bette Davis famously said growing old isn’t for sissies.

Anne B. Newman, director of the University of Pittsburgh Center for Aging and Population Health, supports that idea. People who live long lives either follow a healthy lifestyle or better “tolerate the burden of disease,” she said.

Older people, she said, must track blood pressure, cholesterol and blood-glucose levels because medications for those conditions extend the lives of seniors sometimes more prolifically than exercise and a healthful diet. In some studies, frail people benefit most from lifestyle changes.

At 80 or older, “hardly anyone is free of chronic disease,” Dr. Newman said. “People eventually develop cardiovascular disease, cognitive decline and loss of lung function. Age is the highest risk factor for chronic disease and we often see these conditions in people with no risk factors except age.”

American men generally live three fewer years than women but have a more compressed period of poor health of 1.5 years before death, with women on average living three years with poor health before dying.

Older adults may need to carry more weight than younger adults. The ideal body mass index of 25 or lower for most people expands to 25 to 27 for older adults, with BMIs as high as 30 showing no impact on mortality rates. Still people with a BMI higher than 27 can face mobility problems from the added weight, Dr. Newman said.

Debate is underway: Should American health care pay less attention and devote fewer dollars to prolonging the lives of elderly adults with serious chronic illnesses, and shift the focus to disease prevention and expansion of health span in older adults? Joint replacement, she said, is one procedure that expands lifespan by improving mobility and quality of life.

Reasons for Americans’ poor life-expectancy ranking include cardiovascular risk factors, lower socioeconomic factors and higher infant-mortality rates, Dr. Newman said. United States also has more accidental and violent deaths than other countries. “The U.S. is behind in a lot of metrics and Sweden is the most exemplary country.”

Her department offers 10 keys to good aging that combine lifestyle factors and medical treatmentsproven to benefit the aging crowd.

“I don’t think anyone thought there was so much potential to modify the aging process,” Dr. Newman said. “The basic teaching is that aging is inevitable. I do think it is inevitable, but it also is possibly modifiable.”