By Will Dunham

WASHINGTON, Oct 22 (Reuters) - Having more years of formal education delays the memory loss linked to Alzheimer's disease, but once the condition begins to take hold, better-educated people decline more rapidly, researchers said on Monday.

Their study, published in the journal Neurology, tracked memory loss in a group of elderly people from New York City's Bronx borough before they were diagnosed with Alzheimer's or another form of old-age dementia.

Every year of education delayed the accelerated memory decline that precedes dementia by about 2-1/2 months, according to the researchers at Yeshiva University's Albert Einstein College of Medicine in New York.

But once this memory loss began, the rate of decline unfolded 4 percent more quickly for each additional year of education, the researchers said.

Someone with 16 years of schooling might experience memory decline 50 percent more quickly than another person with just four years education, based on the findings.

Alzheimer's disease is a degenerative brain malady that is the most common form of dementia among the elderly.

"An elderly person who starts to see memory loss might well deteriorate fairly rapidly, particularly if he or she has a high education or high IQ," Charles Hall, a professor of epidemiology at Albert Einstein College of Medicine who led the study, said in a telephone interview.

"And this is important to clinicians to know so they can advise their patients that things might well get very bad very fast, whereas in a lot of other people the decline is relatively gradual over a long period of time," Hall added.

People with more years of formal education appear to have a greater "cognitive reserve," Hall said, referring to the brain's ability to keep working despite damage.

While better-educated people may be diagnosed with Alzheimer's later than people with less education, it appears they have suffered brain damage but their "cognitive reserve" was able to hide and delay the effects, the researchers said.

The study started in the 1980s, tracking 488 people born from 1894 and 1908 and giving them periodic memory tests. The findings published on Monday were based on 117 of them who eventually developed Alzheimer's or another dementia.

Most of the participants were followed until either death or diagnosis of dementia. Those diagnosed with dementia were followed for up to about 16 years, with an average of six years.

The study included people with postgraduate education as well as others with fewer than three years of elementary school. Hall noted that levels of education that people received varied much more in the early part of the 20th century than they do now.

Hall said the study was valuable in part because it examined memory loss before a formal diagnosis of Alzheimer's. Other studies have detected quicker memory loss among more highly educated people after diagnosis of Alzheimer's.

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