Sense of Smell May Predict Risk for Cognitive Decline

alz-assnTwo studies presented at the 2014 Alzheimer’s Association International Conference (AICC) in Copenhagen this month demonstrated that a decrease in the ability to identify odors was significantly associated with loss of brain cell function and progression to Alzheimer’s disease. There is growing evidence that the decreased ability to correctly identify odors is a predictor of cognitive impairment and an early clinical feature of Alzheimer’s disease.

Researchers from the Harvard Brain Study, evaluated olfaction via the University of Pennsylvania Smell Identification Test (UPSIT) in 215 clinically normal elderly individuals and administered a battery of cognitive tests. Also measured was the size of two brain structures – the entorhinal cortex and the hippocampus and levels of amyloid deposits in the brain.  They found that a smaller hippocampus and a thinner entorhinal cortex were associated with worse smell identification and worse memory.

From 2004 to 2010, Columbia University Medical Center researchers studied a multi-ethnic group of 1,037 senior citizens without a diagnosis of cognitive dysfunction to determine whether a relationship exists between the inability to identify smells and a diagnosis of mild cognitive decline. The research showed that in subjects with low UPSIT scores, “210 participants transitioned to either dementia or Alzheimer’s disease (AD) during follow-up two to four years after initial UPSIT was administered. Transition to dementia and AD was correlated with lower odor-identification scores on the UPSIT.”

Of all of the subjects who were followed over the years,  lower odor-identification scores were significantly associated with the transition to dementia and Alzheimer’s disease. For each point lower that a person scored on the UPSIT, the risk of Alzheimer’s increased by about 10%. In addition, lower baseline UPSIT scores, but not measures of verbal memory, were significantly associated with cognitive decline in participants without baseline cognitive impairment. “Odor identification deficits were associated with the transition to dementia and Alzheimer’s disease, and with cognitive decline in cognitively intact participants, in our community sample.”

For many years, olfactory deficits have been associated with Parkinson’s disease. “Impairment of olfaction is a characteristic and early feature of Parkinson’s disease. Recent data indicate that >95% of patients with Parkinson’s disease present with significant olfactory loss.”

According to the Alzheimer’s Association, “In the face of the growing worldwide Alzheimer’s disease epidemic, there is a pressing need for simple, less invasive diagnostic tests that will identify the risk of Alzheimer’s much earlier in the disease process.”

This same sense of urgency applies to Parkinson’s disease.