A decreased sense of smell appears to be linked to the onset of Alzheimer’s, according to an article published in JAMA Neurology. Share on Pinterest Loss of sense of smell may indicate onset of some types of dementia, researchers say. Previous research has associated olfactory loss, or anosmia, with cognitive decline, mild cognitive impairment (MCI) or Alzheimer’s disease (AD). It may also be a marker for Lewy body and vascular dementia. Autopsy studies have linked a loss of ability to identify odors with the plaques and tangles in the olfactory bulb, entorhinal cortex and the cornu ammonis regions of the hippocampus. Markers of early detection can help prevent or delay these diseases, and olfactory impairment may be an important clinical marker and predictor of these conditions, helping to identify those at risk. Rosebud Roberts, of the Mayo Clinic in Rochester, MN, and coauthors assessed the sense of smell of 1,430 cognitively normal individuals, with an average age of 79.5 years; approximately half were men and half were women. The participants were enrolled in the population-based, prospective Mayo Clinic Study of Aging between 2004 and 2010, and were clinically evaluated at baseline and every 15 months through 2014.

Olfactory decrease matches increase in memory loss The test they used involved six food-related and six non-food-related smells (banana, chocolate, cinnamon, gasoline, lemon, onion, paint thinner, pineapple, rose, soap, smoke and turpentine). Participants had to scratch, sniff and select one of four possible options, for a score to be computed. Over an average of 3.5 years of follow-up, the authors identified 250 new cases of MCI among the 1,430 participants. There was 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. The findings suggest an association between olfactory impairment, incidental MCI and progression from aMCI to AD dementia, and confirm previous studies linking olfactory impairment with cognitive impairment in late life.