The Association Between Alopecia Areata and Iron Deficiency Anemia: A Large-Scale Population-Based Case-Control Study

Background: Alopecia areata (AA) is a chronic autoimmune disorder characterized by non-scarring hair loss and commonly coexists with other autoimmune diseases, suggesting systemic immune dysregulation. An association between AA and iron deficiency anemia (IDA) has been proposed, though prior studies have yielded conflicting results. Objective: Our aim was to examine the association between AA and IDA in a large, population-based cohort. Methods: We conducted a retrospective case-control study using data from a health maintenance organization (HMO) serving approximately 2.35 million individuals. We included 33,401 AA patients diagnosed between 2005 and 2019, matched 1:2 by age and sex with 66,802 controls without AA. Diagnoses of AA and IDA were confirmed through clinical coding by board-certified dermatologists and primary care physicians. Statistical analyses employed Kruskal-Wallis, Pearson's χ², and Fisher's exact tests. Results: IDA prevalence was significantly higher in AA patients than in controls (15% vs. 10%; OR 1.61, 95% CI: 1.55-1.67; p < 0.01). IDA preceded AA in 40% of cases, followed AA in 58%, and occurred concurrently in 2%. Limitations: The retrospective design limits causal inference. Conclusion: This study reinforces an association between AA and IDA, highlighting the need to assess and manage IDA as a potential treatable comorbidity in AA patients.