Although diseases like are very common among those
age 85 and over, cognitive impairment and memory loss are not an
inevitable part of aging.
Many healthy older people who have no cognitive impairment live
the remainder of their lives without experiencing dementia, an
ongoing study shows.
According to the report, which appeared in the January 11 issue
of the journal Neurology (www.neurology.org), about 50 percent of
people age 85 and over will develop some degree of Alzheimer's
disease. However, the remaining 50 percent will remain cognitively
normal until death.
For people ages 65 to 85, an average of 10 percent will develop
Alzheimer's, a fatal degenerative disease, characterized by a
decline in memory and mental functioning, and eventually physical
functioning as well.
This research is part of The Oregon Brain Aging Study, which
began in 1989. Instead of studying only patients with Alzheimer's
to find out what goes wrong, researchers at the Veterans Affairs
Medical Center and the Oregon Health Sciences University in
Portland are observing healthy ``super-normal'' elderly to find out
how their brains avoid Alzheimer's.
In the Neurology study, the researchers evaluated data from 19
people age 85 and older who had no signs of cognitive impairment
and who were free of complicating health problems like high blood
pressure, diabetes, stroke, brain tumors or cardiovascular disease.
(This population subset may account for about 1 percent of people
over 85, the authors wrote.)
Every six months to a year, these study participants underwent
cognitive evaluations, neurological examinations and magnetic
resonance imaging scans.
On average, these individuals lived to about 94 years old.
Pathologists examined the brains after death for evidence of
plaques and tangles, the physical hallmarks of Alzheimer's disease.
Over the course of the study, seven of the participants
developed dementia, and three developed cognitive impairment.
However, nine were cognitively normal until their deaths.
Of the nine cognitively normal people, brain autopsies revealed
evidence of the plaques and tangles that are indicative of
Alzheimer's disease in two. The remaining seven people had very few
physiological markers of Alzheimer's.
Study co-author Dr. Melvyn Ball, a professor of neurology and
pathology at the Oregon Health Sciences University, said that
people who have the pathological markers of Alzheimer's but who did
not display any behavioral signs of the disease may have been
protected by their ``neuronal reserve.''
The theory of neuronal reserve says that certain people have
more brain cells and better connections between these cells.
According to this theory, ``you might in fact have to accumulate
many more of these pathology lesions before you'd get into trouble
with your memory compared with the next person, who doesn't have
quite so many nerve cells,'' said Ball. ``Until you knock out a
certain proportion of the connections of the nerve cells, you won't
actually develop evidence [of Alzheimer's] clinically.''
He also noted that these people may have eventually showed
clinical signs of Alzheimer's had they lived long enough because
plaques and tangles begin developing long before clinical signs of
the disease emerge.
``It's very hard to actually pin down precisely when this
process gets started,'' Ball explained. ``It's a very subtle
thing.''
Because the brain begins changing before behavior does, Ball
said it is important for doctors to try to look for the signs of
Alzheimer's early.
``In family practice, there's a great need to continue to work
at devising more accurate ways to pick up the earliest subtle
changes in the person who is prone to Alzheimer's,'' he continued.
``So if any drug comes on the market that seems to have promise,
you could start to get them on it early rather than late in the
disorder.''
Of the 10 patients in the study who showed clinical signs of
dementia, two did not show the pathological signs of Alzheimer's in
their brains. Ball said that aside from plaques and tangles, many
factors likely play a role in Alzheimer's, and different factors
may contribute to the condition in different people.
``It would be nave to think that we'll put our finger on one
microscopic abnormality and say, 'That's the reason they got
dementia,''' he said. ``It's a very complicated problem. We're
looking at abnormal memory, and to this day, we don't even know how
normal memory works.''
What protects these people from dementia, even after living over
100 years? According to Ball, genetics might play a strong role. In
the near future, he said, ``it will be possible to slowly dissect
out which, if any, of the genes that these 'super-normals' have
that might explain how they came not to get the Alzheimer
changes.''
Neil Buckholtz, chief of the dementias of aging branch at the
National Institute on Aging in Bethesda, Md., said that the health
of one's blood vessels may be another factor.
``There is a relationship between vascular disease and
dementia,'' Buckholtz said. ``Cardiovascular disease or
cerebrovascular disease may interact in terms of plaques and
tangles and certainly in terms of the cognitive dementia component
too.''
He also explained that oxidative damage (from cellular
processing of oxygen) and inflammation are potential factors, and
therefore, antioxidant vitamins and anti-inflammatory drugs may
help certain people avoid dementia. However, researchers will not
know more until the completion of a number of current clinical
trials, he said.
