To find out, the Columbia researchers administered a standard smell identification test to 77 people with mild cognitive impairment (MCI), whose symptoms included moderate memory loss. Studies have shown that people with MCI go onto develop Alzheimer's at a higher rate than average. For this reason, an early-detection test for the disease should score more "hits" within the MCI group.
In the Columbia study, the test subjects sniffed cards scented with familiar odors such as menthol and peanuts. Then the people were scored on how accurately they could identify the odors. Two years after taking the test, 19 of the 77 people in the MCI group developed Alzheimer's. It turned out that the people who had initially scored the lowest were, as a group, more likely to develop Alzheimer's than people who scored higher on the test.
However, the study does not show that the smell test can accurately identify particular individuals who are at high risk of developing Alzheimer's, cautions Yaakov Stern, Ph.D., an Alzheimer's researcher at Columbia who assisted in the study. That would require much larger studies.
"Olfactory deficits in patients with mild cognitive impairment predict Alzheimer's disease at follow-up," by D. P. Devanand and others. The American Journal of Psychiatry, vol 157 (September 2000), pp. 1399-1405.