Did the link between anosmia and migraine exist before the COVID-19 pandemic? A population-based cohort study

The purpose of this study was to investigate the connection between anosmia and migraine. Anosmia and migraine are both disorders that can significantly impact quality of life. Olfaction and headache are clinically associated and share biological connections through interactions between the olfactory and trigeminal sensory systems. The COVID-19 pandemic brought increased attention to anosmia and its neurological implications, including headache. However, despite this renewed interest, epidemiological studies examining the association between anosmia and migraine independent of COVID-19 remain limited.

We conducted a retrospective cohort study using data from Korea's National Health Insurance claims database. The study population (n = 3,435,193) consisted of individuals aged ≥20 years who were randomly selected from participants in the 2009 national health screening program. Participants were classified into two groups: the anosmia group (n = 8270), which included individuals diagnosed with anosmia between 2006 and 2008, and a control group (n = 3,426,923) drawn from remaining participants. Both groups were followed from 2011 to 2020 to assess the incidence of migraine.

The incidence rate of migraine was higher in the anosmia group (21.85 per 1000 person-years) than in the control group (16.47 per 1000 person-years). After adjusting for multiple covariates, the risk of developing migraine remained significantly elevated in the anosmia group compared with the control group (adjusted hazard ratio=1.19, 95% confidence interval=1.13-1.25).

This National cohort study provides insight into the increased incidence of migraine disorder in those with a prior anosmia diagnosis even prior to the COVID-19 pandemic. Additional research is needed to understand mechanisms responsible for this connection between the olfactory and trigeminal systems in neurologic disease.