Dulled Sense of Smell Might Predict Alzheimer's

By Ed Edelson
HealthDay Reporter
Tuesday, July 3, 2007; 12:00 AM

TUESDAY, July 3 (HealthDay News) -- Losing your sense of smell might be an early sign of cognitive decline, a new study finds.

"It has been reported before that people who already have mild cognitive impairment have difficulty with odors," noted lead researcher Robert S. Wilson, a professor of neuropsychology at the Rush Alzheimer's Disease Center in Chicago.

However, "no one has started [a study] with people with no cognitive impairment at all," he said. But the new research, published in the July issue of theArchives of General Psychiatry, did just that.

In the study, Wilson's group enlisted 589 older people, averaging close to 80 years of age, to take a test in which 12 common odors were placed under their noses. The participants were scored from one to 12 on their ability to match a smell to one of four alternatives.

They then were evaluated once a year for five years in tests of neurological and cognitive function.

Over that time, 177 of the participants developed the kind of mild cognitive impairment that can be a warning sign of future Alzheimer's disease. The risk of developing such mental impairment was associated with a decrease in odor identification ability. Those who scored below the average score on the odor identification test were 50 percent more likely to develop mild cognitive impairment than those who scored above average, the researchers say.

The study results fit in with one leading theory surrounding the development of Alzheimer's disease, Wilson said. That notion centers on the idea that Alzheimer's begins with trouble in certain specialized areas of the brain, then spreads more widely until it involves the major thinking areas.

"There could be several years in which you wouldn't expect to see problems with thinking but problems with functions such as smell," he said.

The theory received lukewarm support from Dr. Sam Gandy, chairman of the Alzheimer's Association's National Scientific Advisory Council. Gandy is also director of the Farber Institute for Neurosciences at Thomas Jefferson University in Philadelphia.

"The idea is attractive, since the smell area of the brain is involved in the course of the disease," Gandy said.

And yet, "reports that problems with a person's sense of smell may be an early indicator of memory and thinking problems have appeared in the scientific literature at several occasions over the past 20 years," he pointed out. Still, "no observation has been particularly strong nor have they been replicated by other scientists," Gandy said.

More detailed studies are needed to assess the possibility of a connection between smelling ability and changes in mental function, he said.

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