Jennifer Stamps, a graduate student at the University of Florida's McKnight Brain Institute Center for Smell and Taste, and colleagues found peanut butter worked well to test for smell sensitivity.
Stamps was shadowing at the clinic of Dr. Kenneth Heilman, the James E. Rooks distinguished professor of neurology and health psychology in the University of Florida's College of Medicine, and asked why patients were not tested for their sense of smell.
The ability to smell is associated with the first cranial nerve and is often one of the first things to be affected in cognitive decline.
The researchers had the patients sniff a bit of peanut butter with each nostril while the opposite nostril was closed. They used a ruler to measure the point at which people detected the smell of the peanut butter.
Those with a confirmed diagnosis of early-stage Alzheimer's could smell the peanut butter with their right nostril, but not their left, the study said.
Stamps said she used peanut butter because it is a "pure odorant" only detected by the olfactory nerve -- instrumental in the sense of smell -- and because it is easy to obtain.
The findings were published in the Journal of the Neurological Sciences.