WASHINGTON -- Health care costs now eat up more than 10 percent of the family income of nearly 50 million Americans under 65, according to a new study by government researchers.

Their estimates, published today in The Journal of the American Medical Association, are based on federal consumer surveys done in 1996 and 2003 that counted all out-of-pocket health care costs.

"We found that the prevalence of high financial (health) burdens increased across the population as a whole and among several subgroups between 1996 and 2003," said Jessica Banthin and Didem Bernard, researchers at the federal Agency for Healthcare Research and Quality.

By 2003, they calculate there were 48.8 million individuals (19.2 percent of the non-elderly population) living in families that spent more than 10 percent of household income on medical care, an increase of 11.7 million people since 1996.

Of this group, 18.7 million (7.3 percent of the total population) were in families spending more than 20 percent of family income on medical care.

Among those more likely to face higher-than-average health care costs were low-income individuals, those with individual rather than group coverage, people in the pre-retirement age bracket of 55 to 64, women, people living outside metro areas and people with chronic medical conditions.

"We also noted that high out-of-pocket burdens are associated with delaying or forgoing medical care for financial reasons, behavior that can have severe consequences for those in poor health," Banthin said.

The researchers said their review "highlights the high costs associated with non-group health insurance policies." People who bought individual coverage were nearly three times more likely to pay 10 percent or more of their family income to health costs than people with any other type of insurance coverage, including no coverage at all.

In addition, Banthin and Bernard said their measure of health care service burden -- out-of-pocket costs other than insurance premiums -- can be used to identify people who are underinsured, although they technically have coverage.

They calculate that 17.1 million people had inadequate financial protection from high out-of-pocket costs in 2003, including 9.3 million who were in private, employment-related plans, 1.3 million with individual coverage and 6.6 million with public coverage.

Health care costs have been rising faster than inflation and the overall economy in the United States for many years. Out-of-pocket payment for health care by patients rose from $162 billion in 1997 to $236 billion in 2004, out of a total national health bill of nearly $2 trillion.