Carla K. Johnson, Associated Press
July 3, 2007 — 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's no cure for the more than 5 million Americans with the disease.
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 odor 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.
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 decline.
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 odors 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 odors.
