And they warn that the fast-growing toll, now at 125 million among a population of 276 million, will reach 157 million by 2020. One-fifth of Americans have two or more chronic illnesses, complicating their care and making it more expensive.

The nation is unprepared to cope with the growing burden of chronic disease, with annual medical bills alone expected to almost double to $1.07 trillion by 2020, Dr. Gerard Anderson of Baltimore's Johns Hopkins University told a meeting Wednesday of 1,000 chronic disease specialists.

"We think it's the major public health challenge that could affect all Americans," Anderson said.

While doctors have made major advances in treating certain chronic illnesses, they cause 70 percent of all U.S. deaths, reports the federal Centers for Disease Control and Prevention, which convened the meeting to explore ways to better prevent and fight long-term illness.

It's a difficult subject partly because so many different diseases qualify. Simple allergies may not kill someone, but require a lifetime of medication and doctor visits. Heart disease can require even more complex drug therapy, surgery and testing. At the other extreme is Alzheimer's disease, eventually requiring round-the-clock care.

Preventive care - weight management, disease screening, nutrition, exercise, geriatric assessments for the elderly - can stave off many chronic diseases. But it takes longer than writing a prescription, and few insurers reimburse fully, Anderson said.

He quoted an insurance director who said his patients demand payment for such care as in vitro fertilization, not ways to prevent illnesses they might not get for decades.

Then he cited a rural Maryland physician's lament about his diabetic patient, an overweight farmer whose insurance pays for a 20-minute visit, just enough time to test his blood sugar and adjust medication. The doctor says helping the man lose weight would do more good, but he is not paid to do that.

Already 60 million Americans suffer multiple chronic illnesses, a number expected to reach 81 million by 2020 as the population ages, Anderson reported.

Someone without a chronic illnesses pays an average of $182 a year in out-of-pocket health expenses, Anderson said, compared with $369 in out-of-pocket payments by patients with one chronic illness and $1,106 for someone battling three or more.

Total annual health costs for someone with one chronic illness are more than five times higher than for a healthy person - $6,032 vs. $1,105 - and rise even higher the more disabling the chronic illness is, he reported.