The epidemic of obesity sweeping America is the prime culprit behind recent sharp increases in Medicare spending, researchers report.

The reason: Older, heavier people are much more likely to enter the program with pre-existing medical issues, the experts say.

"The rise in Medicare spending is largely traced to the doubling of obesity among the elderly and obesity-related conditions like diabetes, high blood pressure, bad cholesterol and so on," said lead author Kenneth E. Thorpe, the Robert W. Woodruff Professor and Chair of the Rollins School of Public Health at Emory University, Atlanta.

However, policy makers are not taking the burden of obesity and its related illnesses into account as they look at ways to reduce costs to preserve Medicare, experts say.

While increases in the program's cost have been attributed to causes such as medication costs, hospital and doctors fees, 90 percent of the increases can be attributed to people entering the program with diabetes, metabolic syndrome and other diseases associated with obesity, concluded a report published in the Aug. 22 online issue of Health Affairs.

The researchers analyzed data from two major federal studies -- published in 1987 and 2002 -- to assess trends for disease prevalence and Medicare expenditures.

They found that the number of obese Medicare recipients nearly doubled during that time period, while the cost of treating these patients nearly tripled -- from 9.4 percent of Medicare spending in 1987 to 25 percent of expenditures by 2002.

The number of patients receiving treatment for five or more medical conditions also rose -- from 31 percent in 1987 to more than half of recipients in 2002. These patients used up more than three-quarters of Medicare spending by 2002, compared to 52 percent of expenditures in 1987.

In addition, Thorpe said, almost half the Medicare population meets the clinical definition of "metabolic syndrome" -- a collection of unhealthy factors, including hypertension, cholesterol abnormalities, a waist circumference greater than 40 inches in men and 35 inches in women, and hyperglycemia. Studies have shown that people with metabolic syndrome have a 1.5 times increased risk for coronary heart disease.

"Physicians are [also] much more aggressively treating patients today compared to even five to 10 years ago," Thorpe pointed out.

That's true even for non-obese patients. In their study, Thorpe and his colleague David Howard found the number of normal-weight Medicare patients being treated for five or more conditions rose from 11.5 percent in 1987 to 16 percent in 2002. The portion of Medicare costs earmarked for these patients rose from 19.6 percent in 1987 to 24.1 percent in 2002, the study found.

More aggressive treatment does help patients, of course. In 2002, almost 60 percent of Medicare patients being treated for five or more conditions said they were in excellent or good health, compared with 33 percent of similar patients in 1987, Thorpe and Howard found.

But as a larger number of unhealthy Medicare recipients live longer, costs rise.

Many of the factors driving these trends are being ignored, Thorpe said.

"Most of the debate about how to deal with the growth in entitlements really is ignoring these key facts," he said. "Most of the reforms on the table have nothing to do with what's driving the growth of Medicare spending up in the first place," he added.

Real efforts to stop the obesity epidemic could put the brakes on this trend, Thorpe said. "We need to recognize that we need to do much more in terms of primary prevention -- diet, exercise and nutrition -- not only among the existing Medicare beneficiaries, but among the near-elderly, those 55 to 64," he said. "These people will be entering Medicare with rates of chronic disease disability that we have never seen."

According to the researcher, heightened awareness of the dangers of smoking has cut the number of people smoking from 30 percent to 20 percent since the 1950s. Similar programs might curb obesity, too.

One expert agreed that people need to make significant lifestyle changes to bring down Medicare costs and improve their health.

"There is a great need to get to people before they even enter Medicare," said Mary R. Grealy, chair of Medicare Today and president, Healthcare Leadership Council, a medical industry lobbing group. "But, at any age, there are things people can do to make lifestyle changes and reduce the incidence of disease and the need for a variety of medications," she added.

Grealy believes that, in addition to government programs, private employers and health insurers need to concentrate on obesity, diabetes and other conditions linked with being overweight to curb health care costs. "We really have to focus on prevention," she said.

Another expert thinks that extending Medicare to younger people -- those aged 55 to 64 -- would bring a lot of healthier people into the program before chronic illness appears. That could save dollars, said Robert M. Hayes, the president of the Medicare Rights Center, a consumer watchdog group.

"It's common sense," said Hayes. "If we give people better care, they will be healthier and live longer," he added.

"A lot of us think that extending Medicare eligibility to people 55 to 64 would be a good idea," Hayes said. "Because a lot of folks in the decade before eligibility lose their employment, lose their health coverage and are effectively uninsured. They hit Medicare coverage in pretty bad shape. It would be a humanitarian and cost-effective measure to figure out how to bring people into Medicare before age 65."