Older adults who have difficulty recognizing such common odours as lemon, banana and cinnamon may be in the first stages of Alzheimer's disease, according to a report in the Archives of General Psychiatry.
Difficulty in identifying odours has been associated with the mild cognitive impairment that often transitions to Alzheimer's disease. Research suggests that even before the symptoms of Alzheimer's develop, hallmark tangles develop in certain areas of the brain that may be associated with the processing of smells.
However, little is known about factors that predict the development of mild cognitive impairment.
Robert S. Wilson of Rush University Medical Center, Chicago, and colleagues studied the sense of smell of 589 healthy adults who had an average age of 79.9 years and no signs of cognitive impairment and followed them for five years, testing them for signs of mental decline.
The participants took a smell identification test, sniffing 12 familiar odours and matching each to one of four alternatives. They then returned for 21 cognitive tests every year for five years.
Over the course of study, 177 individuals (30.1 per cent) developed mild cognitive impairment. The risk of developing mild cognitive impairment increased as odour identification decreased, so that those who scored below average (eight) on the odour identification test were 50 per cent more likely to develop the condition than those who scored above average (11).
This association did not change when stroke, smoking habits or other factors that might influence smell or cognitive ability were considered.
Not all of those who scored poorly in the smell test went on to have cognitive problems, Wilson said, but difficulty in identifying odours can be an early manifestation of Alzheimer's disease.
