A new study by Mayo Clinic researchers has reported that the loss of one’s sense of smell may be a predictor of cognitive impairment and Alzheimer’s disease. The finding could lead to earlier intervention in seniors who are developing the disease. The findings were published online on November 16 in the journal JAMA Neurology.
The study authors stressed that in order to increase the opportunity to delay or prevent mild cognitive impairment or Alzheimer disease, early detection is essential. They noted that olfactory (sense of smell) impairment may be an important clinical marker and predictor of these neurological impairments and may help identify individuals at increased risk. Therefore, the objective of the study was to examine associations of impaired sense of smell with mild cognitive impairment and its progression to Alzheimer’s disease.
The study group comprised 1,630 seniors enrolled in the prospective (forward-looking) Mayo Clinic Study of Aging from 2004 through 2010. The subjects were clinically evaluated at baseline and every 15 months through 2014. Participants (N = 1630) were classified as having normal cognition, mild cognitive impairment (amnestic or nonamnestic), and dementia. There are two types of mild cognitive impairment: amnestic, which significantly affects memory as well as other cognitive functions (individuals with this type of cognitive impairment are three to four times more likely to develop Alzheimer’s disease than someone without mild cognitive impairment); and non-amnestic, which affects cognitive functions other than memory (this form of mild cognitive impairment is more often related to non-Alzheimer’s dementia, such as frontotemporal dementia or dementia caused by Lewy bodies. The researchers administered the Brief Smell Identification Test (B-SIT) to evaluate olfactory function.
The investigators found that, among the 1,630 participants who were cognitively normal at the time of the smell test, 33 died before follow-up and 167 were lost to follow-up. Among the 1,430 cognitively normal participants, the average age was 79.5 ± 5.3 years, 49.4% were men, the average duration of education was 14.3 years, and 25.4% were Apolipoprotein-ε4 (APOE-ε4) carriers. APOE-ε4 is a major genetic risk factor for cognitive decline, Alzheimer’s disease, and early mortality. Over an average 3.5 years of follow-up, there were 250 cases of mild cognitive impairment among 1,430 cognitively normal participants. The researchers found an association between decreasing sense of smell, as measured by a decrease in the number of correct responses in B-SIT score, and an increased risk of amnestic mild cognitive impairment. There was no association with nonamnestic mild cognitive impairment. There were 64dementia cases among 221MCI cases. The B-SIT score also predicted progression from amnestic mild cognitive impairment to Alzheimer’s disease, with a significant correlation with worsening B-SIT scores.
The authors concluded that olfactory impairment is related to amnestic mild cognitive impairment and its progression to Alzheimer’s disease. They noted that their findings were consistent with those of previous studies that have reported associations of olfactory impairment with cognitive impairment in late life and suggest that olfactory tests have the potential to screen for mild cognitive impairment as well as mild cognitive impairment that is likely to progress.