Abstract
Background
Olfactory dysfunction has been reported in early stages of Alzheimer's disease and other neurodegenerative diseases (Hawkes, 2003). It has also been reported in individuals at higher risk of developing dementia including mild cognitive impairment patients (Djordjevic, et al., 2008) and apolipoproteine4 allele (APOEe4) carriers (Graves, et al., 1999). We have also reported significant olfactory dysfunction in memory complainers as compared to non-memory complaining individuals (Sohrabi, et al., 2008, 2009).
Methods
The current longitudinal study investigates whether olfactory function at baseline can predict future cognitive function. Participants were assessed on a number of cognitive and olfactory measures. The inclusion criteria consisted of a baseline cognitive function above the cut-off score for dementia on Mini Mental Status Examination (MMSE = 24) and CAMCOG-R (= 81), and normal olfactory function (as assessed by Sniffin Sticks). Participants were assessed annually for 3 years. Blood samples were collected for APOE genotyping at baseline. The cohort was divided into two groups: cognitively declined and cognitively non-declined individuals. Participants were considered to be “cognitively declined” if their score on last assessment with CAMCOG-R was 1 SD below the baseline performance.
Results
308 participants, aged 46-86 years old, were recruited for this longitudinal study. The cohort consisted of 68% female, and 32% were APOEe4 carriers. There was significant association between baseline olfactory function (as assessed by Sniffin' Sticks) and general cognitive performance (as assessed by CAMCOG-R) after three years of follow up. As expected, logistic regression analysis indicated that baseline olfactory score was a significant predictor of cognitive decline even after controlling for the effects of age, sex, APOEe4 genotype and education. There was no significant difference between the APOEe4 carriers and non-carriers on olfactory or cognitive functions.
Conclusions
The results of this study indicated that olfactory function can potentially predict age-related cognitive decline. However, the potential value of olfactory function in screening for future cognitive decline and dementia needs further longitudinal and clinical studies. The implications of these findings will be discussed.