, according to new research findings.
Olfactory dysfunction is common in late life and well documented among people with Alzheimer’s disease. However, it was unknown whether faster olfactory decline predicts either onset of Alzheimer’s disease or structural brain changes associated with Alzheimer’s disease.
Dr. Jayant M. Pinto
In a study published online in Alzheimer’s and Dementia, Jayant M. Pinto, MD, and his colleagues at the University of Chicago Medical Center reported that among older adults with normal cognition at baseline, people who experienced rapid loss of sense of smell were more likely to be subsequently diagnosed with mild cognitive impairment (MCI) or dementia, compared with those who did not.
Participants were recruited from Rush University’s Memory and Aging Project, a longitudinal cohort of older adults who undergo yearly cognitive and sensory exams, including a scratch test of 12 common smells to identify. The Rush study “was ahead of the curve in looking at smell,” Dr. Pinto said in an interview. “It gave us a very valuable resource with which to attack these questions.”
Dr. Pinto has long investigated links between smell and accelerated aging; in 2014 his group published the finding that olfactory dysfunction could predict death within 5 years in older adults, and in 2018 they reported that olfactory dysfunction could predict dementia.
Smell and cognition over time
For the current study, Dr. Pinto said, “we were able to look at the question not just using a single point in time, but a more granular trajectory of smell loss. Measuring change year by year showed that the faster people’s sense of smell declined, the more likely they were to be diagnosed with MCI or Alzheimer’s disease.”
Dr. Pinto and his colleagues evaluated results from 515 adults (mean age 76.6, 78% female, 94% White) with no cognitive impairment and at least 3 years of normal results on smell tests at baseline. The subjects were followed for a mean 8 years. One hundred subjects (19%) were diagnosed with MCI or dementia by the end of the study period. A subset of the cohort (n = 121) underwent structural magnetic resonance imaging (MRI) between their final smell tests and the study’s end. Of these, most still had normal cognition; 17 individuals had MCI.
Patients’ individual trajectories of smell loss were mapped as slopes. After adjusting for expected differences in age and sex, the investigators found steeper decline associated with greater risk of incident MCI or dementia (odds ratio, 1.89; 95% confidence interval, 1.26-2.90; P < .01). The risk was comparable to that of carrying an apo E ε4 allele, the key risk variant for late-onset Alzheimer’s disease, but was independent of apo E status. The association was strongest among subjects younger than 76 years.