From Medical Correspondent Dan Rutz

ATLANTA (CNN) -- Four out of 10 Americans have something medically wrong that never gets completely healed. That's the sobering message from this week's chronic disease conference held by the Centers for Disease Control and Prevention.

As baby boomers age and the U.S. population becomes increasingly older, health experts are concerned the country may hit a mid-life health crisis.

Those at the 13th National Conference on Chronic Disease Prevention and Control say a lot of pain and suffering associated with aging can be avoided if people take health matters into their own hands.

Robert Kahn, a psychology and public health professor at the Institute for Social Research at the University of Michigan, said just accepting the inevitable is the wrong approach.

"The idea that the main task of old age was to let go of things one by one and ultimately, of course, life itself," he said.

Kahn discourages talk about aches and pains -- or what he calls the "organ recital." He said the focus should be on what people of all ages can do to keep going strong.

"One of the things our research found that I think is most exciting is that the physical differences among elderly people are only explained about one third genetically and about two thirds by the cumulative effects of their lifestyle -- what they've done and what's been done to them," he said.

Kahn preaches a three-step plan for health aging; protect against disease through regular check-ups and diet, keep physically and mentally fit and stay engaged in life with good friends and productive pursuits.

Those who inherit a higher risk of disease may need to get started on their healthy lifestyles earlier in life.

"Diabetes is one of the leading chronic conditions in the United States. At Grady Hospital in Atlanta, most patients learn to control their diabetes with diet and exercise alone.

Peggy Mann, age 43, said she was headed toward an early grave with her weight and diabetes out of control.

"I realized from being very ill from diabetes that I had to take charge of my own care, that no one could do it for me," she said.

The idea of patients being in charge of chronic disease is catching on. For many, it serves as a natural way to keep their conditions in check for years.

"Diabetes is a self-managed disease and if you have it , you have to take care of it and manage it," said Kristina Ernst of the Grady Hospital Diabetes Clinic. "You're sort of the captain of the ship and we're coaches."

For Peggy Mann self-management has meant moving from a wheelchair to walking five miles a day.