DIAGNOSIS OF ANOSMIA IN MIDDLE AGE INCREASES ALZHEIMER'S DEMENTIA RISK, BUT NOT IN THE ELDERLY.

Abstract

Introduction: Many studies have reported that patients with anosmia have an increased incidence of dementia later in life. However, most of these were conducted only on older people aged 65 or older, and there was a lack of research on middle-aged subjects aged 40-65.

Methods: We conducted a retrospective cohort study utilizing Korea's National Health Insurance claims data. The study targeted participants aged 40 years and above, randomly selecting 40% of individuals who underwent the 2009 national health check-up. The cohort was divided into two groups: the anosmia group (n = 8,023), consisting of individuals diagnosed with anosmia between 2006 and 2008, and the control group (n = 2,680,534), comprising the remaining participants. Subsequently, we followed up on the participants, monitoring the occurrence of Alzheimer's and vascular dementias from 2011 to 2020.

Results: After adjusting for various factors across all subjects, the incidence of Alzheimer's dementia increased in the anosmia group compared to the control group [hazard ratio (HR) 1.15, 95% confidence interval (CI) 1.04-1.28]. When comparing the two groups based on age 65, the risk ratio for developing dementia in patients with anosmia compared to controls of the same age significantly increased in those under 65 years of age (HR 1.28, 95% CI 1.07-1.54), but did not increase in those over 65 years of age (HR 1.10, 95% CI 0.97-1.24). Vascular dementia was not statistically associated with anosmia.

Conclusion: Anosmia diagnosed in middle age increases the risk of Alzheimer's dementia, whereas this is not the case in old age.