Today, the condition is known as Alzheimer's disease (AD), or dementia of the Alzheimer's type (DAT). Some experts are starting to drop the "s," calling the condition Alzheimer disease (paralleling the name change from Down's syndrome to Down syndrome), but most authorities continue to use the "s"--Alzheimer's disease.

Alzheimer's disease is sometimes called "pre-senile dementia," and sometimes "senile dementia." In medical jargon, the term "senile" simply means "old." In common usage, however, it denotes a loss of mental faculties. As a result, some people get confused by "pre-senile dementia". In common usage, it seems like a contradiction in terms-- dementia before you've lost mental acuity. Actually, in medical jargon, "pre-senile" simply means "younger than 65". Doctors use "pre-senile dementia" to describe Alzheimer's disease that develops before age 65, and "senile dementia" for Alzheimer's that develops after 65. Either way--pre-senile or senile--it's the same disease.

The term "dementia" may cause problems as well. In common usage, "demented" often implies wildly out of control. In medical jargon, it simply describes a loss of cognitive function. Many people with Alzheimer's develop behavior problems, but some do not.

Who Has Alzheimer's Disease?

During the 1960s, researchers considered Alzheimer's disease a rare disorder. But during the last 30 years, scientists have recognized that it's fairly common, in fact, the leading cause of age-related dementia.

Many famous people have suffered Alzheimer's disease: British statesman Winston Churchill, actress Rita Hayworth, and most recently, former President Ronald Reagan.

An estimated 4 million Americans currently have Alzheimer's disease. In rare cases, it begins to develop before age 50. A small proportion of people show signs of Alzheimer's in their 50's. But the vast majority of Alzheimer's sufferers develop the disease after 60.

According to a 1989 study, 10.3 percent of Americans 65 and older have Alzheimer's disease (Evans, D.A. et al "Prevalence of Alzheimer's Disease in a Community Population of Older Persons: Higher Than Previously Reported," Journal of the American Medical Association (1989) 262:2551).

But that overall figure is misleading. According to a large survey of retired individuals, risk of Alzheimer's disease changes considerably during the elderly years:

From age 65 to 74, about 10 percent of people are affected. From age 75 to 84, the figure rises to 20 percent. And for those 85 and older, Alzheimer's afflicts 47 percent. (Evans, D.A. et al. "Estimated Prevalence of Alzheimer's Disease in the U.S." Millbank Quarterly (1990) (68:267)

Currently the U.S. population is aging. People over 85 have become the nation's fastest-growing age group. Because this is also the group most affected by Alzheimer's disease, experts warn that unless researchers discover how to prevent it, by the year 2020, some 7 percent of those over 65 might have Alzheimer's, with that figure rising as high as 15 percent by 2050.

Samuel Lewis (c) copyright 1995