Diagnosis of Anosmia in Middle Age, But Not in Older Adulthood, Increases Alzheimer Dementia Risk

Many studies have reported that patients with anosmia exhibit an increased incidence of dementia later in life. However, most of these studies have focused exclusively on individuals aged 65 or older, leaving a gap in research on middle-aged subjects (40-65 years).

We conducted a retrospective cohort study using Korea's National Health Insurance claims data. The study targeted participants aged 40 years and above by 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), comprising individuals diagnosed with anosmia between 2006 and 2008, and the control group (n=2,680,534), consisting of the remaining participants. Subsequently, we followed the participants to monitor the occurrence of Alzheimer and vascular dementia from 2011 to 2020.

After adjusting for various factors, the incidence of Alzheimer dementia was significantly higher in the anosmia group compared to the control group (hazard ratio [HR], 1.15; 95% CI, 1.04-1.28). Stratification by age revealed that the risk of developing dementia was significantly elevated in anosmia patients under 65 years (HR, 1.28; 95% CI, 1.07-1.54), whereas no significant increase was observed in those over 65 years (HR, 1.10; 95% CI, 0.97-1.24). Vascular dementia was not statistically associated with anosmia.

A diagnosis of anosmia in middle age increases the risk of developing Alzheimer dementia, while no such increase is observed in older individuals.