The overall life expectancy of American men could rise to 87 years by the year 2040, while the average American woman could live to 92 during the same period, a new study said.

The study released Sunday also showed the number of Americans over age 85 may grow to nearly 24 million in the next 50 years, twice as many as previously expected and 10 times the current level.By the year 2040, the population in the United States over age 65 may catapult to 87 million, or one-quarter of the entire U.S. population, a figure 20 million higher than what the census has projected and three times the current level, the study said.

The study by the University of Southern California and the National Institute of Aging, an arm of the National Institutes of Health, was reported in The Los Angeles Times.

There are many variables in population projections, but the major difference between U.S. Census Bureau figures and the new, higher projections is the optimism that the USC and national institute researchers share about medicine's ability to prolong life over the next 50 years, the papers said.

Edward Schneider, USC's dean of gerontology and one of three authors of the study, told the newspaper that the statistics reveal government and families could face "some very complex and costly problems, the magnitude of which this nation has not even begun to estimate."