Impaired Sense of Smell Associated with Mild Cognitive Impairment, Progression to Alzheimer Disease Dementia


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An impaired sense of smell was associated with amnestic mild cognitive impairment (predominantly memory loss) and the progression to Alzheimer disease dementia in a study of older patients with an average age of nearly 80 in Minnesota, according to an article published online by JAMA Neurology.


Previous research has suggested associations of loss of a sense of smell with cognitive decline, mild cognitive impairment (MCI) or Alzheimer disease (AD) dementia.


Rosebud O. Roberts, M.B., Ch.B., of the Mayo Clinic, Rochester, Minn., and coauthors sought to replicate previous findings in a large study. Participants’ sense of smell was assessed through a test with six food-related and six nonfood-related smells (banana, chocolate, cinnamon, gasoline, lemon, onion, paint thinner, pineapple, rose, soap, smoke and turpentine).


The study included 1,430 cognitively normal individuals, with an average age of 79.5 years, who were nearly evenly divided between men (49.4 percent) and women.


Over an average of 3.5 years of follow-up, the authors identified 250 incident (new) cases of MCI among the 1,430 participants. The authors report an association between a decreasing ability to identify smells, as measured by a decrease in the number of correct answers in the smell test score, and an increased risk of amnestic MCI (aMCI). There appeared to be no association between a decreased sense of smell score and nonamnestic MCI (naMCI), which can affect other thinking skills.


The authors also reported 64 dementia cases among 221 individuals with prevalent MCI. A decrease in the frequency of any or AD dementia was associated with increasing scores on the smell test. The worst smell test score categories were associated with progression from aMCI to AD dementia.


Potential explanations for the current findings involve neurodegenerative changes in the olfactory bulb and brain regions that involve smell.


“Clinical implications of our findings are that odor identification tests may have use for early detection of persons at risk of cognitive outcomes,” the authors conclude.

(JAMA Neurol. Published online November 16, 2015. doi:10.1001/jamaneurol.2015.2952. Available pre-embargo to the media at


Editor’s Note: Authors made conflict of interest and funding/support disclosures. Please see the article for additional information, including other authors, author contributions and affiliations, financial disclosures, funding and support, etc.


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