Feb. 20 (Bloomberg) -- Fewer elderly Americans have memory loss or other symptoms of dementia today than their counterparts did a decade ago, a nationwide survey found.

About 8.7 percent of participants aged 70 and older had some degree of cognitive impairment -- ranging from mild memory loss to Alzheimer's disease -- in 2002, down from 12.2 percent in 1993, according to the report in the journal Alzheimer's & Dementia. That translates into hundreds of thousands fewer people with mental impairment than would otherwise be expected.

Better education, income and heart health may help explain the trend, said researchers from the University of Michigan Medical School in Ann Arbor. Previous studies showed mental stimulation and education can build up a ``cognitive reserve'' as people age, while drug therapy for the heart also protects arteries leading to the brain, they said.

``From these results, we can say that brain health among older Americans seems to have improved in the decade studied, and that education and wealth may be a big piece of the puzzle,'' said Kenneth Langa, the lead author of the study and associate professor of internal medicine. ``What we may be seeing here is the accumulated effects of better education and better cardiovascular prevention,'' he said in a statement.

About 40 percent of the decline can be attributed to the increase in education and wealth between the two groups of seniors in the study that surveyed about 11,000 Americans. The more educated and financially secure participants who did have memory and other impairments were more likely to die quickly, within two years, than others with a similar health status.

The findings come from the Health and Retirement Study, a national survey funded by the U.S. National Institute on Aging.

Diabetes, Aging

The reduction in memory loss and other mental deficits may not last if the current increase in the number of Americans with type 2 diabetes continues, the researchers said. Even if the overall rate of decline persists, the total number of Americans with Alzheimer's disease and other forms of dementia are likely to rise because of the aging U.S. population, they said.

``The trend toward improved cognitive status is consistent with a dramatic decline in chronic disability among older Americans over the past two decades,'' said Richard Suzman, director of NIA's social and behavioral research program. ``It will be important to pinpoint the influence of factors such as increased education, exercise, medications, cardiovascular health, and lifestyle to discover which ones contributed to this trend.''

To contact the reporter on this story: Michelle Fay Cortez in Minneapolis at mcortez@bloomberg.net

Last Updated: February 20, 2008 12:50 EST