Unmarried middle-age men and women face twice the risk of dying within 10 years as those still living with their spouses, a study showed Thursday.

The study of 7,651 people nationwide came to no conclusion about why unmarried people in the group died at the higher rate, but suggested divorce was a key factor in putting people at risk.Researchers at the University of California at San Francisco found 23 percent of the men between 45 and 54 who lived alone or with someone other than a spouse died within a decade. Only 11 percent of married men studied died during that period.

Of the unmarried women in the same age group, 7.7 percent died. Only 4 percent of married women died. The higher death rate seemed connected to low income, with poorer women at greater risk.

The gap between the married and unmarried groups slightly narrowed as the individuals grew older, the study said.

Men who had been previously married were at the most risk, researchers said.

"Of particular interest is that both men who live alone and those who live with someone other than a spouse are equally disadvantaged for survival," said Maradee Davis, an associate professor of epidemiology and biostatistics who led the study. "The critical factor seems to be the presence of a spouse."

Because of the high divorce rate in the United States and the trend for older adults to live alone if widowed, there should be "general concern about the social isolation, health and well-being of older adults living alone," she said.

The study, which is consistent with previous research, also found the percentage of people living without spouses increased with age and was higher for women than men in all the age groups.