The brains of people with Alzheimer's disease may show severe plaques and tangles.

People with stronger language skills early in adulthood may be at a lower risk of experiencing symptoms of Alzheimer's disease decades later, a new study suggests.

In this week's online edition of the journal Neurology, U.S. researchers who studied the brains of 38 Catholic nuns after death found those with strong written language scores in their late teens or early 20s were less likely to develop memory problems in later life compared with those with lower language scores.

"A puzzling feature of Alzheimer's disease is how it affects people differently," study author Dr. Juan Troncoso, of Johns Hopkins University in Baltimore, said in a release.

"One person who has severe plaques and tangles, the telling signs of Alzheimer's disease in their brains, may show no symptoms affecting their memory. Another person with those same types of plaques and tangles in the same areas of the brain might end up with a full-blown case of Alzheimer's disease. We looked at how language ability might affect the onset of symptoms."

The study looked at two groups: women with memory problems and plaques and tangles in the brain and women with normal memory with or without signs of Alzheimer's disease in the brain.

The researchers analyzed essays that 14 participants wrote as they entered the convent, studying the average number of ideas expressed for every 10 words and how complex the grammar was in each essay.

Language scores were 20 per cent higher in women without memory problems compared to those with those with memory problems. The grammar score did not show any difference between the two groups.

Protective mechanism?

Troncoso's team also found the brains of women without symptoms of Alzheimer's had larger neurons. It's possible the larger neurons compensated for the plaques and tangles that usually indicate Alzheimer's, acting as a protective mechanism, the researchers said.

"Our results show that an intellectual ability test in the early 20s may predict the likelihood of remaining cognitively normal five or six decades later, even in the presence of a large amount of Alzheimer's disease pathology," Troncoso said.

It's not clear whether the genetic factors or more studying bestows the apparent protection from dementia despite signs of disease in the brain.

A previous study in men also found larger neurons among those who had plaques and tangles in their brain without clinical evidence of Alzheimer's.

"It is interesting that the nuns in the study with better language skills in their youth avoided memory problems in later life," Dr. Susanne Sorensen, head of research at the Alzheimer's Society in the United Kingdom, said in a statement on the group's website.

"However, the research is in a very small, select group and it would be difficult to say at this stage if language skills could really predict dementia."

Rebecca Wood, chief executive of the Alzheimer's Research Trust in the U.K., agreed with the researchers that a possible implication of the study is that intellectual ability early in life may have predictive value for staying cognitively normal decades later.

"However, prominent exceptions exist, including authors like Terry Pratchett and Iris Murdoch, who developed dementia despite their linguistic brilliance."

The study was funded by Johns Hopkins University Alzheimer’s Disease Research Center, the National Institutes of Health, the Nun Study, the National Institute on Aging, the University of Kentucky Alzheimer’s Disease Center, the Abercrombie Foundation and the Kleberg Foundation.