New research examining a 12-year period, 1998 to 2010, suggests that the prevalence of self-reported falls among older adults is on the rise.

Falling is the most frequent cause of injury among older adults and about a third of older adults fall each year. Researchers from the University of Michigan Health System analyzed data from 1998-2010 among adults age 65 and older and found an 8 percent increase in falls -- which translates to a relative increase of nearly 30 percent.

"We expected an increase because older adults are getting older and there are more 80- and 90-year-old adults than before, but we were very surprised to find that the increase in falls was not due to the changing demography," Christine Cigolle, lead author of the study, said in a statement. "We saw a higher number of falls across all age groups -- not just the oldest -- and that was unexpected."

For the study, researchers looked at trends in falling in a nationally representative sample of middle-aged and older adults in the Health and Retirement Study, which is conducted by the University of Michigan Institute for Social Research on behalf of the National Institute of Aging.

Falling was defined as at least one self-reported fall in the preceding two years. Among all adults 65 and older, the two-year prevalence of self-reported falls increased from about 28 percent in 1998 to 36 percent in 2010.

Despite the greater prevalence of reported falls, however, the study did not find that older adults were reporting more fall injuries.

"It's possible that older adults are more aware of fall risk and may be more likely to report it now than before," Cigolle, who is also a member of the Institute of Gerontology and the Institute for Healthcare Policy and Innovation, said. "However, if the prevalence of falls is actually increasing as much as it seems to be, we need to do more work to identify possible factors and how we can address what we know to be a high risk among a vulnerable group."

The findings appear in JAMA Internal Medicine.