Sense of smell declines with advancing age, a loss of capacity already correlated with broader neurodegeneration and progression towards cognitive impairment and dementia. Here, researchers correlate the loss of sense of small with numerous other aspects of aging, as well as type 2 diabetes, a condition associated with a greater risk of age-related disease and mortality because most diabetics are significantly overweight. Excess fat tissue accelerates aging via mechanisms such as increased generation of senescent cells and increased chronic inflammation.
Olfactory dysfunction is common in aging and associated with dementia and mortality. However, longitudinal studies tracking change in olfactory ability are scarce. We sought to identify predictors of interindividual differences in rate of olfactory identification change in aging. Participants were 1780 individuals, without dementia at baseline and with at least 2 olfactory assessments over 12 years of follow-up (mean age = 70.5 years; 61.9% female), from the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K). Odor identification was assessed with the Sniffin' Sticks. We estimated the impact of demographic, health, and genetic factors on rate of olfactory change with linear mixed effect models.
Advancing age, manufacturing profession, history of cerebrovascular disease, higher cardiovascular disease burden, diabetes, slower walking speed, higher number of medications, and the APOE ε4 allele were associated with accelerated odor identification decline. Multi-adjusted analyses showed unique associations of age, diabetes, and ε4 to olfactory decline. In 1531 participants who remained free of dementia during follow-up, age, cardiovascular disease burden, and diabetes were associated with accelerated decline. Of these, age and diabetes remained statistically significant in the multi-adjusted model.
In conclusion, demographic, vascular, and genetic factors are linked to rate of decline in odor identification in aging. Although some olfactory loss may be an inevitable part of aging, our results highlight the importance of vascular factors for the integrity of the olfactory system, even in the absence of dementia.