Understanding subjective measures of olfaction and cognition : A study on the occurrence of subjective olfactory and/or cognitive decline and their effect on future behavioral performance

Abstract: Dementia is a growing burden for society, and it is of interest to discover it at an early stage. Both subjective cognitive decline (SCD) and subjective olfactory decline (SOD) has been associated with future cognitive decline and dementia. However, subjective measures have often been criticized and are still not fully understood. I aimed to examinate the frequency of SCD and SOD and whether they are likely to measure different things and what their longitudinal effects are. The baseline sample (N=784, 35-90 years, 51% female) were split into reported SCD, SOD, combined subjective olfactory and cognitive decline, and controls. Between-subjects and within-subjects statistical tests were conducted on a subset of participants (N=307, 45 to 90 years, 52% female) comparing SCD and SOD and their olfactory ability, cognitive performance, and demographics. In the baseline sample, a total of 21.1% reported a SOD whereas only 9.9% reported a SCD, only 2.7% reported both. SOD individuals had an emerged olfactory decline at follow up, their olfactory performance was associated with performance in several cognitive tests, this was not the case for the SCD individuals. The SOD and the SCD groups differ from each other, and they appear to be rather independent from each other. They might be complementary in understanding the aging brain.