July 2, 2007 (Insidermedicine)

Problems identifying common odors among older adults may be associated with an increased risk of developing mental impairment, such as Alzheimer’s disease, say researchers in an article published in the Archives of General Psychiatry.

Alzheimer’s disease is a progressive brain disorder in which plaques and tangles form in the brain, gradually destroying a person’s memory and ability to learn, reason, communicate, and carry out daily activities.

It is now understood that people who have difficulty identifying odors have a more rapid mental decline and a shorter transition time from mild impairment to Alzheimer’s disease. Little is known, however, about the factors that predict the development of mild mental impairment.

In the present study, researchers studied nearly 600 healthy older adults and asked them to identify 12 familiar odors, and scored them on their ability to do so. At the beginning of the study, and again every year for up to five years, they underwent a medical history, neurological exam, and mental function testing.

During the study 30% developed mild mental impairment and the risk increased as their ability to recognize odors decreased. In fact, those who scored below average on the odor identification test were as much as 50% more likely to develop mental impairment compared to those who scored above average. Impaired ability to identify odor was also associated with lower mental ability scores at the beginning of the study and a faster decline in memory of past experiences, words, and symbols.

It is thought that even before symptoms of Alzheimer’s disease begin, the tangles and plaques characteristic of the disease may develop in areas of the brain responsible for processing smells. Because problems identifying odors are associated with other diseases, such as Parkinson’s, researcher suspect that other mechanisms may be involved.

Based on the findings, odor identification testing may be a useful tool for identifying people at risk of developing Alzheimer’s disease.