CHICAGO (Reuters) - Americans are living longer, so why not lower the eligibility age for Medicare?

That prescription might sound upside down: rising longevity often is used as an argument for delaying Medicare eligibility past age 65. However, one of the country's top experts on geriatric medicine actually thinks Medicare should start covering preventive healthcare when we turn 50.

Dr. Linda Fried, dean of the Mailman School of Public Health at Columbia University in New York, says that could help people not just live longer, but enjoy more healthy years. Meanwhile, Medicare would save money on treatment of chronic illnesses in seniors.

Much of Fried's research is focused on promotion of healthy aging, and the latest evidence shows people who get to age 60 in relatively good health are likely to stay healthy.

"The investment would be worth it," she says. "It won't cost Medicare or the country more money, but having people living not just longer but healthier is essential to being able to experience the benefits of longer lives."

Medicare celebrates its 50th anniversary this summer, and its impact on the health of seniors has been dramatic. Since 1965, people over age 65 are living longer with far lower rates of death from chronic disease. The program has evolved and improved along the way, adding home health services, hospice care and prescription drug coverage, just to name a few innovations. The anniversary is a great time to ask what can be done better in the years ahead.

Fried lays out a prevention-oriented vision in an article in a new issue of the research journal of the American Society on Aging.

The core of her argument: age 50 to 65 is the period of greatest risk of disability due to cancer, heart disease and stroke, obesity and diabetes.

"It’s a high-risk group - the time when really bad health things emerge, and so much of it is completely preventable," she says.

Research also suggests that it is never too late to get results through prevention.

"Seventy percent of cancers could be prevented if we can get people to stop smoking and improve their diets," Fried says. "And there’s clear evidence that a substantial portion of strokes and coronary heart disease can be avoided by blood pressure screening."

BETTER INSURANCE

The Affordable Care Act already is improving health insurance coverage in the 50-64 year old population, and a sizeable portion of the under-65 population is covered through workplace insurance. The overall percentage of uninsured Americans age 50 to 64 stood at 11 percent last year, down from 14 percent in 2013, according to The Commonwealth Fund.

Still, Fried argues many policies leave people under-covered for preventative medicine, and that Medicare should be reformed to start interacting with its future enrollees at an earlier age.

She calls for extending clinical prevention to age 50 with a full set of vaccinations, screenings and preventive services. She also wants Medicare to cover oral healthcare, vision and hearing examinations, hearing aids and glasses, all of which are key to preserving healthy, independent living as we age.

That is just for starters. Fried also envisions getting Medicare involved in activities that would help seniors maintain physical health and mental cognitive ability. One way to do that would be to have Medicare "prescribe and support" programs such as walking school buses - where seniors get their daily exercise by walking children to school, or Experience Corps, the senior volunteer program.

Fried was a co-founder of the Experience Corps in the 1990s, along with Marc Freedman, founder and Chief Executive Officer of Encore.org.

The program trains older adult volunteers to work with low-income students in public elementary schools, but it also was designed to be a public health intervention aimed at improving cognitive ability and social activity for older people. Research has documented higher levels of physical metabolism and improved cognitive function in volunteers who spend 15 hours weekly with Experience Corps.

Fried thinks Medicare could even provide incentives to get people involved.

"Medicare could cover your co-pays for every year of volunteer work, or even a year or two of free Part B coverage. It would be a great way to invest in the health of enrollees," she says.

(Reporting by Mark Miller; Editing by Beth Pinsker, Lauren Young and Andre Grenon)