Olfactory deficit is an early sign of neurodegenerative diseases, such as Alzheimer’s disease (AD), and is related to age-related cognitive and physical function decline. However, underlying biological processes are not fully understood. Identifying shared lipid metabolites may shed some light. In 656 Baltimore Longitudinal Study of Aging participants (mean age:70.5 years), we examined associations of plasma lipids with olfaction, cognitive impairment (including AD), cognition, and physical function, after adjusting for demographics. Plasma lipid metabolites, assayed via FIA- and LC-mass spectrometry, were analyzed as 6 lipid classes. Odor identification was measured via the 16-item Sniffin’ Sticks. Cognition was measured via a neuropsychological battery. Physical function measures included gait speed, chair stands, and balance. Very long-chain and long-chain sphingomyelins and glycosylceramides were positively associated with olfaction, select cognitive measures (Trail Making Test-Part A, Digit Symbol Substitution Test, Purdue Pegboard Test), and physical function. Sphingomyelins were also associated with memory (California Verbal Learning Test immediate recall) and cognitive impairment (all p < 0.05). Only very long-chain sphingomyelins and glycosylceramides affected associations between olfaction and outcome measures (Δβ:10-25.9%). Plasma sphingomyelins and glycosylceramides, especially those with long-chain carbons, may at least in part explain the relationship between olfaction and functional outcomes. Future omics studies may provide additional mechanistic insights.
Greig et al. (Tue,) studied this question.