Difficulty identifying common smells such as lemon, banana and
cinnamon may be the first sign of Alzheimer's disease, according to a
study that could lead to scratch-and-sniff tests to determine a
person's risk for the progressive brain disorder.
Such tests could be important if scientists find ways to slow or
stop Alzheimer's and the severe memory loss associated with it. For
now, there is no cure for the more than 5 million Americans with the
Researchers have long known that microscopic lesions considered the
hallmarks of Alzheimer's first appear in a brain region important to
the sense of smell.
"Strictly on the basis of anatomy, yeah, this makes sense," said
Robert Franks, an expert on odour perception and the brain at the
University of Cincinnati. Franks was not involved in the new study,
appearing in Monday's Archives of General Psychiatry.
But lead author Robert Wilson of Chicago's Rush University Medical
Centre said a diminishing sense of smell is not cause for panic.
"Not all low scorers went on to have cognitive problems," Wilson
Other studies have linked loss of smell to Alzheimer's, Franks said,
but this is the first to measure healthy people's olfactory powers and
follow them for five years, testing along the way for signs of mental
A dozen familiar smells
In the study, 600 people between the ages of 54 and 100 were asked
to identify a dozen familiar smells: onion, lemon, cinnamon, black
pepper, chocolate, rose, banana, pineapple, soap, paint thinner,
gasoline and smoke.
For each mystery scent, they heard and saw a choice of four answers.
For cinnamon, they were asked aloud: "Fruit? Cinnamon? Woody? Or
coconut?" while also seeing the choices in text.
A quarter of the people correctly identified all the odours or missed
only one. Half of them knew at least nine of the 12. The lowest-scoring
quarter of the people correctly identified eight or fewer of the odours.
The subjects took 21 cognitive tests annually over the next five
years. About one-third of the people developed at least mild trouble
with memory and thinking.
Four errors or more
The people who made at least four errors on the odour test were 50
percent more likely to develop problems than people who made no more
than one error. Difficulty identifying odours also was associated with a
higher risk of progressing from mild cognitive impairment to
The researchers took into account age, gender, education and a
history of strokes or smoking, and still found lower scores predicted
higher risk of cognitive decline.
Older people should report a loss in smell to their doctors, said
Claire Murphy, an Alzheimer's researcher at San Diego State University
who was not involved in the new study. The problem could be caused by a
polyp in the nose or infected sinuses, she said.
"If a person is old and has a very good sense of smell, that's a
very good sign," Murphy said.
The study was funded by the National Institute on Aging and the
Illinois Department of Public Health. – (Sapa)
Smell test for dementia
How well we really smell