The proportion of older middle-aged Americans who report disabilities related to mobility increased significantly from 1997 to 2007, in contrast to the disability decline that has been found among Americans ages 65 and over, says a new study by the RAND Corporation and the University of Michigan.

Researchers found a rise in the proportion of Americans between the ages of 50 and 64 who reported mobility-related difficulties or the need for help in daily personal care activities such as getting out of bed, says the journal Health Affairs.

The reason for the increase is not clear, although many of those reporting disabilities say they are due to health problems that began in their 30s and 40s.

"Although the overall rate of needing help with personal care among this group remains very low—less than 2 percent—this rise in disability is reason for concern," says Linda Martin, the study's lead author and a senior fellow at RAND, a nonprofit research organization. "It does not bode well for future trends for the 65 and older population, plus there are substantial personal and societal costs of caring for people of any age who need help."

Researchers examined disability trends among people in that 50-to-64 age group by analyzing information from the 1997 to 2007 National Health Interview Survey, a nationally representative effort that asks thousands of community-dwelling Americans each year about a broad range of issues regarding their health status.

More than 40 percent of people in that age group reported that because of a health problem they had difficulty with at least one of nine physical functions, and many reported problems with more than one. Over the study period, researchers noted a significant increase in the number of people reporting that a health problem made it difficult for them to stoop, stand for two hours, walk a quarter mile, or climb 10 steps without resting.

There also was a significant increase in the proportion of people who reported needing help with personal care activities of daily living, such as getting in or out of bed or getting around inside their homes.

"This is a disappointing trend with potentially far-reaching and long-term negative consequences," says Richard Suzman, director of the Division of Behavioral and Social Research at the National Institute on Aging, which funded the study.

"If people have such difficulties in middle age, how can we expect that this age group—today's baby boomers—will be able to take care of itself with advancing age? If it continues, this trend could have a significant effect on the need for long-term care in the future."

From 1997 to 2007, increasing proportions of people in that age group attributed their need for help to back or neck problems, diabetes, and depression, anxiety, or emotional problems. By 2005-07, the four most common causes for needing help were these three plus arthritis or rheumatism. People who reported these conditions as causes were most likely to report that the ailments started at ages 30 to 49 years.

The reported increases in conditions causing disability may reflect real deterioration of health or improved awareness of conditions as a result of diagnosis and treatment. It also could be that improved medical care has extended the lives of people whose disabilities began early in life and who might not have survived to age 50 in earlier decades.

Despite continuing concerns about obesity in the U.S., those needing help didn't cite obesity as an important cause of their limitations.

"We have this uptick of people in their 50s and early 60s who say they need help with their daily activities of living and we're not sure why," says study co-author Vicki Freedman, a research professor at the Institute for Social Research at the University of Michigan. "But the patterns suggest the need for prevention and early intervention before the age of Medicare eligibility."

Other authors of the study are Robert Schoeni and Patricia Andreski of the Institute for Social Research.

RAND Health, a division of the RAND Corporation, claims to be the nation's largest independent health policy research program, with a broad research portfolio that focuses on quality, costs, and health services delivery, among other topics.

The University of Michigan Institute for Social Research claims to be the world's largest academic social science survey and research organization, and a world leader in developing and applying social science methodology.

Established in 1949, the Institute for Social Research conducts what it claims are some of the most widely cited studies in the nation, such as the Thomson Reuters/University of Michigan Survey of Consumer Attitudes, the American National Election Studies, the Monitoring the Future Study, and the Health and Retirement Study. ISR researchers also collaborate with social scientists in more than 60 nations on various projects.