Dementia warning.

Aging populations of the world, beware: Disorders of memory and thinking will become much more common with more people living into their 90s, according to a long-term study in England and Wales.

Even people who reach age 80 free of Alzheimer's disease or other dementias stand a good chance of later developing some form of mental incapacity, says a team led by epidemiologist Carol Brayne of the University of Cambridge in England.

From 1990 to 1992, Brayne and her coworkers assessed the mental status of 13,004 people age 65 and older at six rural or urban sites. All were receiving medical care unrelated to mental problems. Of 12,387 individuals who died by 2004, there were 2,566 who had developed dementia. A comparable number had developed severe memory and thinking impairments that fell short of dementia.

Dementia rates rose sharply as people got older, the researchers report in the October PLoSMedicine. Prevalence rates ranged from 6 percent for those who died between ages 65 and 69 to 58 percent for those who died at age 95 or older.

Overall, dementia affected 38 percent of women and 22 percent of men, a significant disparity even after accounting for the tendency of women to live longer than men, the scientists say.--B.B.