Olfaction and risk of dementia in a biracial cohort of older adults

Abstract

Objective: Prior studies indicate that olfactory function may be an early marker for cognitive impairment, but the body of evidence has been largely restricted to white populations. Methods:We studied 2,428 community-dwelling black and white older adults (baseline age 70-79 years) without dementia enrolled in the Health, Aging, and Body Composition (Health ABC) study. Olfaction was measured as odor identification (OI) with the 12-item Cross Cultural Smell Identification Test in year 3. We defined incident dementia over 12 years on the basis of hospitalization records, prescription for dementia medication, or 1.5-SD decline in race-stratified global cognition score. We assessed dementia risk associated with OI score (by tertile) using Cox proportional hazards models. All analyses were stratified by race.Results: Poorer OI in older adults without dementia was associated with increased risk of dementia. After adjustment for demographics, medical comorbidities, and lifestyle characteristics, white participants in the poor or moderate OI tertile had greater risk of dementia (adjusted hazard ratio [HR] 3.34, 95% confidence interval [CI] 2.45-4.54; and HR 1.84, 95% CI 1.33-2.54, respectively) compared to those in the good tertile of function. Among blacks, worse OI was associated with an increased risk of dementia, but the magnitude of the effect was weaker (p for interaction 5 0.04) for the poor OI tertile (adjusted HR 2.03, 95% CI 1.44-2.84) and for the moderate tertile (adjusted HR 1.42, 95% CI 0.97-2.10). There was no interaction between OI and APOE e4 and risk of dementia.Conclusions: While the magnitude of the association was stronger in whites, we found that poor OI was associated with increased risk of dementia among both black and white older adults. Olfactory testing may be a simple, inexpensive, and highly sensitive method of identifying older adults at risk for developing dementia, particularly when combined with other early markers.

Predictive value of olfactory impairment for cognitive decline among cognitively normal adults

“…Effect modification by race was examined in one study, which stratified its cohort into black and white. The magnitude of association between olfactory impairment and risk of dementia was significant among both groups; however, the association was weaker among black compared with white participants …”

“…Interestingly, the presence of apolipoprotein E (APOE)‐e4 allele was found to modify the effect of olfactory impairment and cognitive decline in one study, wherein the association was strongest among those who were anosmic with at least one allele (OR 4.93, 95% CI, 1.63–14.91), especially among women (OR 9.71, 95% CI 1.34–70.44). However, a different study found no interaction between APOE genotype and olfactory impairment on incident dementia.…”

“…In another study, decrease in the 13‐item SOIT score was associated with higher risk of developing dementia at 10 years (adjusted OR = 1.12, 95% CI 1.02–1.23) . When BSIT scores were analyzed as tertiles, the unadjusted odds of developing incident dementia among “poor” odor identification group compared to “moderate” or “good” groups was 2.58 (95% CI 2.09–3.19) at the 12‐year follow‐up time …”

“…However, this study included only two longitudinal cohort studies, precluding strong conclusions about the predictive utility of olfactory impairment . Several longitudinal studies have been published since 2012 that support the predictive value of olfactory testing in future cognitive decline …”

Olfactory Dysfunction Predicts Subsequent Dementia in Older U.S. Adults

“…An additional strength that gives this study its broad implications is that olfaction is predictive of dementia even in cognitively intact older adults, extending prior work with high-risk populations and smaller, more-homogenous samples. [1][2][3][4][5][6][7] Why would olfactory dysfunction precede the development of dementia? One potential explanation is that the neuropathology underlying dementia, such as AD (amyloid-b plaques and paired helical filament tau tangles), may begin earlier in the olfactory system than the cortex.…”