Abstract
BACKGROUND: Poor vascular health has been associated with age-related declines in sensory functions, including olfaction. The current study was designed to test the hypothesis that cerebral small vessel disease underlies poor olfactory function due to structural declines in brain regions that support olfaction. METHODS: This study included 166 older adults (mean age = 65.16, ±9.10 years; 68% female) whose olfactory function was measured using the Sniffin' Sticks test. Cerebral small vessel disease was defined as the volume of white matter hyperintensity (WMH) lesions that were measured in T2-weighted images. Morphometry analyses were also performed to identify cortical regions that were both disconnected by WMH and had lower cortical thickness in participants with relatively poor olfaction, and in comparison, to hearing difficulty that has also been linked to vascular disease. Self-reported hearing difficulty was measured using the Revised Hearing Handicap Inventory (RHHI). RESULTS: Higher WMH volume was significantly and uniquely associated with poorer olfactory function or more hearing difficulty (bivariate associations ps ≤ 0.001). Poorer olfactory function, but not more hearing difficulty, was significantly associated with evidence of disconnected cortex where there was also lower cortical thickness within olfactory cortex and other brain regions that support memory and executive functions. These effects appeared to occur with lower episodic memory and slower processing speed. CONCLUSIONS: Together, the results indicate that small vessel disease increases the risk for olfactory or hearing difficulties, and that the former occurs with tissue losses that may explain, in part, why age-related olfactory dysfunction occurs with cognitive declines.