Joint trajectories of episodic memory and odor identification in older adults: Patterns and determinants

Abstract

AbstractBackgroundEmerging evidence suggests that olfactory function is closely linked to memory function. The aims of this study were to assess whether olfactory and episodic memory functions follow similar age‐related decline trajectories, to identify different patterns of decline, as well as determinants of the patterns.MethodsUsing data from the Rush Memory and Aging Project, 1023 dementia‐free participants were identified at baseline and followed for up to 8 years with annual assessments for episodic memory (composite of 7 tests) and odor identification (Brief Smell Identification Test). Data on demographics, medical conditions, social and lifestyle factors were collected by self‐report or medical examination. Trajectories of episodic memory and olfactory function were first modeled individually and then jointly over time using growth mixture models, to identify latent classes (patterns) of the joint trajectories. Multivariate logistic regression was used to identify predictors of the patterns.ResultsBoth episodic memory and olfactory function showed similar trends over the follow‐up interval. Three distinct patterns of joint trajectories, across both functions, were identified; Class 1‐ stable average performance in both functions (n=690, 67.4%); Class 2‐ stable average episodic memory and declining odor identification (n=231, 22.6%); and Class 3‐ decline in both functions (n= 102, 10.0%). Compared to Class 1, people in Class 2 were more likely to be older and male. People in Class 3 were more likely to be older, apolipoprotein ε4 carriers, participate less in cognitive activity, and have lower BMI.ConclusionsEpisodic memory and olfactory function often show similar trajectories in aging, which can be jointly characterized as stable, olfactory decline only, and joint decline.