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Snowdon,
who had accepted a position at the University of Kentucky's
Sanders-Brown Center on Aging, was working with a team of
neurologists and psychologists to devise a battery of tests
for assessing the sisters' mental and physical abilities -
tests that could later be correlated with the results of brain
exams. He joined forces with James Mortimer, an eminent researcher
on aging then at the Minneapolis Veterans Administration Medical
Center, to study the nuns' youthful autobiographies in more
detail, and their relationship led to an interesting discovery:
autopsies by other scientists had shown that the physical
destruction wrought by Alzheimer's didn't inevitably lead
to mental deterioration. The reason, according to one leading
theory, was that some folks might have an extra reserve of
mental capacity that kept them functioning despite the loss
of brain tissue.
So he and
Mortimer, along with University of Kansas psychologist Susan
Kemper, began analyzing the autobiographies for evidence of
such extra capacity. Kemper, an expert on the effects of aging
on language usage, had earlier shown that "idea density" -
the number of discrete ideas per 10 written words - was a
good marker of educational level, vocabulary and general knowledge.
Grammatical complexity, meanwhile, was an indicator of how
well memory was functioning.
Applying
these measures to the sisters' autobiographies, Snowdon and
Kemper found to their astonishment that the elderly sisters
who showed signs of Alzheimer's had consistently authored
essays low in both idea density and grammatical complexity
a half-century or more earlier. One of the lowest-scoring
samples begins: "My father, Mr. L.M. Hallacher, was born in
the city of Ross, County Cork, Ireland, and is now a sheet-metal
worker in Eau Claire." By contrast, one of the highest-scoring
essays conveys the same type of information but in a dramatically
different way: "My father is an all-around man of trades,
but his principal occupation is carpentry, which trade he
had already begun before his marriage with my mother."
Idea density turns out to be an astonishingly powerful predictor
of Alzheimer's disease - at least among the School Sisters
of Notre Dame. Snowdon found by reading nuns' early writings,
he could predict, with 85% to 90% accuracy, which ones would
show the brain damage typical of Alzheimer's disease about
60 years later. "When we first looked at the findings," says
Snowdon, "we thought, 'Oh my God, it's in the bag by the time
you're in your 20s.'"
But Alzheimer's is not that simple. One especially telling
case: Sister Bernadette (not her real name), who had shown
no outward signs of Alzheimer's and whose youthful autobiography
was rich with ideas and grammatical complexity, turned out
at death to be riddled with the plaques and tangles of Alzheimer's
(see diagram). Says Snowdon: "Lesson No. 1 in my epidemiology
training is that there are hardly any diseases where one factor
alone, even in infectious disease, will always cause illness."
These results posed a chicken-and-egg problem: Did higher
brain capacity protect the sisters from developing the symptoms
of dementia, or were those with lackluster biographies already
suffering very early signs of some brain abnormality that
predisposed them to mental decline later? That question remains
unanswered - but follow-up studies, to be published next month
in the journal Psychology and Aging, suggest that exercising
what brain capacity you have offers some protection. While
all the sisters show age-related decline in mental function,
those who had taught for most of their lives showed more moderate
declines than those who had spent most of their lives in service-based
tasks. And that, says Kemper, supports the commonsense idea
that stimulating the brain with continuous intellectual activity
keeps neurons healthy and alive. (Of course, notes Snowdon,
these activities are not absolute protectors. For some, a
genetic predisposition may override even a lifetime of learning
and teaching.)
Another crucial finding from the Nun Study came in 1997,
by which time Snowdon had accumulated some 100 brains for
analysis. He and neurologist Dr. William Markesbery, director
of the Alzheimer's Disease Research Center at the University
of Kentucky, were intrigued by an idea advanced by other researchers
that strokes and other brain trauma might contribute to the
dementia of Alzheimer's disease. Selecting only the brains
of sisters who had earned a bachelor's degree - to eliminate
any differences attributable to education - they found that
among nuns with physical evidence of Alzheimer's in the brain,
those who had evidence of strokes as well almost inevitably
showed outward symptoms of dementia. But only half the nuns
without strokes were comparably afflicted. Says Suzman, of
the National Institute on Aging: "This is one of the first
studies to look at the cardiovascular component of Alzheimer's
disease."
It's also one of the first to suggest a way to stave off
Alzheimer's symptoms. "If your brain is already progressing
toward Alzheimer's," says Snowdon, "strokes or head trauma
(which can produce similar kinds of brain damage) can put
you over the edge." His advice: wear a helmet while biking,
motorcycling or playing contact sports; buckle your seat belt;
and drive a car with air bags. Meanwhile, keep strokes at
bay by keeping your cardiovascular system in shape: avoid
tobacco, get regular exercise and eat a balanced, healthy
diet.
Diet may play a role in Alzheimer's in other ways as well.
In 1998 British researchers announced that Alzheimer's victims
have low concentrations in their blood of the nutrient folate,
also called folic acid. That's an intriguing result, especially
in light of other studies showing that folic acid deficiency
plays a role in some forms of mental retardation in children
and in cognitive problems in adults. So Snowdon began looking
at levels of folic acid, along with 18 other micronutrients
(including beta carotene, magnesium, zinc and cholesterol)
in blood samples of 30 sisters who had died since the study
began.
MORE
>>
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May 14, 2001 | No. 19
COVER
STORIES
The
Nuns' Stories
Hundreds of Roman Catholic sisters have opened up their lives, their memories
and (when they die) even their brains to researcher David Snowdon so that
all of us can better understand what causes Alzheimer's disease and what
can be done to prevent it
TRAVELER'S
ADVISORY
SOCIETY
BEHAVIOR: The Talking Cure...
Australian schools try shaming troublemakers onto the right path
THE
ARTS
CINEMA: Goodbye, Mrs. Tom Cruise. Hello, Nicole
Kidman, star of a bold new movie... Moulin Rouge awakens the dormant
musical
Samantha Lang, a cinematic connoisseur
of sex
MUSIC: Nick Cave, the gloom rocker, blooms
BOOKS: A slim prayer with sales that are
divine
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