July 11 (Bloomberg) -- U.S. adults with chronic health conditions and no insurance run up higher medical costs once they qualify for Medicare than those who had previous coverage, according to researchers.

A study of 2,951 adults diagnosed with long-term ailments before age 65 found that the uninsured reported ``significantly'' more doctors visits and hospitalizations after enrolling in Medicare, the U.S. insurance program for the elderly and disabled. The findings will appear tomorrow in the New England Journal of Medicine.

Lawmakers and presidential candidates are debating how to cover the 45 million Americans without health insurance, about 15 percent of the population. Subsidizing insurance for older adults before they qualify for Medicare may produce some eventual savings by reducing demand for medical services later, according to the study's authors.

``Many Americans may enter the Medicare program in worse health because they have been uninsured,'' J. Michael McWilliams, an author of the study and a researcher at Harvard Medical School in Boston, said in a phone interview today.

Expanding coverage by allowing people younger than age 65 to buy policies run by Medicare or offering other U.S.-financed benefits could ``significantly improve the health of large numbers of Americans without significantly increasing costs,'' McWilliams said in a telephone interview.

Baby Boomers

The number of uninsured adults may increase with the aging of the baby boomers, the generation born after World War II, who will start to qualify for Medicare in 2011, said McWilliams.

The study, by researchers at Harvard and its teaching affiliate, the Brigham & Women's Hospital in Boston, used data on adults from their late 50s through age 64. About 57 percent had chronic conditions such as high blood pressure, diabetes and heart disease.

Adults without insurance were more likely to report declining health before enrolling in Medicare. Those who did had 23 percent more doctor visits and 37 percent more hospitalizations after age 65 than people who had coverage previously.

Covering adults with diabetes and heart disease could produce the most savings because both conditions can lead to life-threatening complications or chronic ailments if left untreated or poorly treated, the study said.

To contact the reporter on this story: Aliza Marcus in Washington at amarcus8@bloomberg.net

Last Updated: July 11, 2007 17:00 EDT