The Evidence: Scientists have found that individuals who are unable to identify certain odors are more likely to experience cognitive impairment. The researchers believe that brain cells crucial to a person’s sense of smell are killed in the early stages of dementia.
Background: The ability to smell is associated with the first cranial nerve, and is often one of the first things to be affected by cognitive decline. 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. As the disease begins to kill brain cells, this often includes cells that are important to the sense of smell.
The Study: Matthew E. Growdon, B.A., M.D./M.P.H. candidate at Harvard Medical School and Harvard School of Public Health, and colleagues investigated the associations between sense of smell, memory performance, biomarkers of loss of brain cell function, and amyloid deposition in 215 clinically normal elderly individuals enrolled in the Harvard Aging Brain Study at the Massachusetts General Hospital. The researchers administered the 40-item University of Pennsylvania Smell Identification Test (UPSIT) and a comprehensive battery of cognitive tests. They also measured the size of two brain structures deep in the temporal lobes — the entorhinal cortex and the hippocampus (which are important for memory) — and amyloid deposits in the brain.
Results: Growdon reports that, a smaller hippocampus and a thinner entorhinal cortex were associated with worse smell identification and worse memory. The scientists also found that, in a subgroup of study participants with elevated levels of amyloid in their brain, greater brain cell death, as indicated by a thinner entorhinal cortex, was significantly associated with worse olfactory function — after adjusting for variables including age, gender, and an estimate of cognitive reserve.
“Our research suggests that there may be a role for smell identification testing in clinically normal, older individuals who are at risk for Alzheimer’s disease,” said Growdon. “For example, it may prove useful to identify proper candidates for more expensive or invasive tests. Our findings are promising but must be interpreted with caution. These results reflect a snapshot in time; research conducted over time will give us a better idea of the utility of olfactory testing for early detection of Alzheimer’s.”
My Take: Exercise may reduce your risk of cognitive decline. For those who are able, aim for a minimum of 150 minutes per week of the equivalent of a brisk walk. I’m Dr. Michael Hunter.
Reference: Alzheimer’s Association. “Smell and eye tests show potential to detect Alzheimer’s early.” ScienceDaily. ScienceDaily, 13 July 2014. <www.sciencedaily.com/releases/2014/07/140713155512.htm>.