Dementia may be set to rise as more people live longer.

So say experts including Carol Brayne, MD, professor of public health medicine at England’s Cambridge University.

Brayne’s team estimates that 487,000 people in the U.S. per year die with dementia -- and that that number will rise to 528,000 people in 20 years.

Dementia becomes more common as people get older. But not everyone develops dementia as they age.

Brayne and colleagues studied more than 12,000 people aged 65 and older living in the U.K.

The researchers followed participants to see who had dementia in the year before death.

Every 10 years, Brayne’s team interviewed participants and gave them a mental skills test covering memory, attention, basic math, and spatial skills.

The highest possible test score was 30 points.

For this study, scores of less than 22 indicate moderate to severe cognitive impairment. Scores of less than 18 note severe cognitive impairment.

“Cognitive impairment” means lower scores on the mental skills test; that is, participants’ mental skills may not have been as sharp.

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Overall, 30 percent of the participants had dementia in the year before they died.

Six percent of those who died at age 65-69 had dementia in the year before death, compared with 58 percent of those who died at age 95 or later.

Dementia was more common among women than men, even after adjusting for the fact that women generally outlive men.

People with higher education levels were up to 10 percent less likely to have dementia than those with less education.

But the study doesn’t prove that education protects against dementia. Observational studies like this one don’t prove cause and effect.

It might be possible to delay or shorten dementia, but well-designed scientific studies are needed to find ways to do that, writes Willem Van Gool, MD, PhD, in a journal editorial.

Van Gool is a neurology professor at Amsterdam’s Academic Medical Centre.

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SOURCES: Brayne, C. Public Library of Science Medicine, October 2006; vol 3: p e397. Van Gool, W. Public Library of Science Medicine, October 2006; vol 3: p e430. News release, Public Library of Science.