Which came first?
Still, the research can't say whether early sparks of Alzheimer's hampered the women's linguistic skills as youth, or whether the women who had developed a high complexity of thought had some protection from the disease in old age.
No one knows how long Alzheimer's disease smolders before a person has noticeable symptoms.
"The reality is, this is a tough area to study," Snowdon says.
He believes that in later life, physical exercise may be more important than mental exercise for brain health.
"If you have a choice between doing New York Times crossword puzzles for a half-hour or walking for a half-hour, get out the door and walk for a half-hour," he says.
Many scientists strongly believe that physical activity is as important to the mind as to the body, perhaps because exercise helps the brain cope with chemicals that interfere with learning and memory.
Though the studies of nuns suggest that mental development early in life is a key to dementia, other research has suggested that even an older brain needs to stretch its legs once in a while.
In 1999, scientists reported in the journal Psychology and Aging that people who prefer intellectually engaging activities — such as learning a language — maintained a better mental edge than those who preferred more passive pastimes (say, watching television). The results are based on a study of 250 adults age 55 and older in Victoria, B.C.
But this research is also dogged by the chicken-and-egg problem. Maybe, says David Hultsch of the University of Victoria, people give up mentally demanding acts because they already sense some decline. "If you can't remember the cards, then you're not going to want to play bridge," he says.
Or both scenarios could be true. And Hultsch and others caution that no study has found that any activity guarantees a person won't get dementia. "Even a person with doctoral degrees can get Alzheimer's."
Pre-dementia research
More recent studies have tried to address the question of which comes first.
In February, Bennett, of the Rush Alzheimer's Center, published research as part of a project studying older Catholic priests and brothers as well as nuns. Clergy at the start of the study in 1994 were quizzed about how they occupied their days. Their activities, which included reading, playing games and listening to the radio, were rated on a scale of 1 to 5, based on their frequency.
A high variety of activities also raised the scores. (Anyone with dementia was excluded.)
Writing in The Journal of the American Medical Association, Bennett reported that more than four years later, 111 of more than 700 people had developed Alzheimer's. However, every 1-point increase in the cognitive activity score was associated with a 33 percent reduction in the risk of Alzheimer's. The higher the score, the lower the dementia risk. |
