CHICAGO (Reuters) - The cost of caring for aging Americans will add 25 percent to the nation's health care bill by 2030 unless people act now to stay healthy, the U.S. Centers for Disease Control and Prevention said on Thursday.

Currently, 80 percent of Americans 65 or older have at least one chronic disease that could lead to premature death and disability, CDC researchers said.

The report, The State of Aging and Health in America 2007, projects that by 2030, 71 million Americans will be over 65, accounting for 20 percent of the U.S. population, up from 10 to 11 percent now.

With the cost of caring for older Americans at three- to five-times greater than care for younger adults, CDC researchers believe policymakers and individuals should take steps to help aging adults forestall chronic disease.

"Given the demographics ... the economic impact on healthcare will be enormous," said Dr. Richard Murray, a vice president at Merck & Co. Inc., whose foundation funded the study.

If people adopt healthier lifestyles, they will not develop the expensive, chronic diseases that raise health costs sharply, such as diabetes, cancer and heart disease.

"We are going to see an increase in health care costs, but the goal has to be to restrain the rate of increase. Prevention is the key to that," said Bill Benson, a health care benefits and policy analyst who advised the CDC on the report.

The report noted that three behaviors -- smoking, poor diet and physical inactivity -- caused almost 35 percent of U.S. deaths in 2000.

SHARP REGIONAL VARIATION

Those three behaviors often lead to the development of the nation's leading chronic diseases: heart disease, cancer, stroke and diabetes, they said.

"Having a chronic disease that's well managed doesn't necessarily put a person at risk for functional decline, but when someone starts developing problems, they are much more at risk," said Lynda Anderson, a chronic disease and aging expert at the CDC.

The report looks at how states are faring in terms of elderly health and providing preventive care such as immunizations and health screenings and taking steps to prevent falls, a major risk for the elderly.

"You have some regions that are doing extremely well in a lot of areas and others that are struggling to get these services to older adults," she said.

Elderly people in Hawaii, for example, are likely to fare better in many key measures of health. The state ranked best in overall health, mental health, and disability and had the lowest percent of obese elderly. But Hawaii ranked last in terms of screening for colorectal cancer.

West Virginia ranked worst in terms of overall health, oral health and disability, while Kentucky had the highest level of elderly people reporting mental health problems. Louisiana reported the highest levels of obesity, with more than 25 percent of the elderly population considered obese.

"There are certainly areas that we need to really pay attention to," Anderson said.

She hopes the data will give state policymakers the right tools to start building prevention programs now, before chronic disease begins.

"We have the opportunity for prevention," Merck's Murray said. "We need to be serious about it."