July 5, 2007
An inability to detect common odors may be an early sign of Alzheimer’s disease, researchers report. Healthy seniors who performed poorly on tests designed to measure detection of everyday smells, such as lemon or paint thinner, were more likely to develop problems with thinking, learning, and memory.
Some were diagnosed with mild cognitive impairment, a type of memory loss that sometimes progresses to Alzheimer’s disease. The study appeared in the Archives of General Psychiatry, a journal of the American Medical Association.
Scientists have previously linked poor scent detection to a more rapid decline in thinking and memory in people who have mild cognitive impairment or Alzheimer’s disease. Problems with the sense of smell have also been linked to the presence of so-called tau tangles, a hallmark of Alzheimer’s, in parts of the brain linked to memory.
In the current study, researchers from Rush University Medical Center in Chicago studied 589 seniors (average age around 80) who were mentally intact. Over the next five years, they were given regular exams to measure memory and thinking skills. They were also given a smell identification test, in which 12 familiar odors, such as banana, chocolate, cinnamon, gasoline, smoke, and turpentine, were placed under their nose. They then had to match the scent with one of four possible choices.
During the study, almost a third of the participants (177 individuals) developed mild cognitive impairment. The researchers found that the worse a person did on the odor identification test, the more likely they were to develop mild cognitive impairment. Men and women who scored below average (eight or fewer correct responses out of 12) on the odor identification test were 50 percent more likely to develop the condition than those who scored above average (11 correct answers). The link between a poor sense of smell and mental decline persisted even when investigators considered other conditions that could affect olfactory responses and cognition, including smoking or having a stroke. Poor odor identification was also associated with lower cognitive scores at the beginning of the study and with a more rapid decline in memory of past experiences, ability to recall words and symbols, and perceptual speed.
“Among older persons without manifest cognitive impairment, difficulty in identifying odors predicts subsequent development of mild cognitive impairment,” the authors conclude. “The findings suggest that olfactory dysfunction can be an early manifestation of Alzheimer’s disease … and that olfactory assessment may be useful for early disease identification.”
Problems with smell are common in old age. They may have many causes and have been linked to other ailments as well, including Parkinson’s disease. So having a problem with smell does not mean that Alzheimer’s is imminent. However, this study and previous studies like it highlight new clues in the early detection of Alzheimer’s, and may shed light on underlying defects in the brain and nervous system that lead to the disease.
The Fisher Center for Alzheimer’s Research Foundation continues to fund critical research into the underlying causes of Alzheimer’s disease. As research findings continue to mount, the hope for a cure draws closer. To learn more, visit www.ALZinfo.org.
Robert S. Wilson; Julie A. Schneider; Steven E. Arnold; et al: “Olfactory Identification and Incidence of Mild Cognitive Impairment in Older Age.” Archives of General Psychiatry, Volume 64, Number 7, July, 2007; pages 802-808.