Onychomycosis and future onset of type 2 diabetes

Introduction: Onychomycosis is a fungal infection of the nail with an increasing prevalence worldwide. Diabetes has been shown to elevate onychomycosis risk by 2.5-3-fold. Objectives: The present study hypothesized that this association may represent a reverse causality relationship, namely that onychomycosis is a risk factor for diabetes, and aimed to determine if the diagnosis of onychomycosis is associated with a future diagnosis of diabetes. Methods: We followed a large cohort of adults insured by the largest health maintenance organization in Israel, for documented diagnoses of onychomycosis and subsequent diabetes between 2000 and 2022. We used multivariate statistical modeling to evaluate hazard ratios for diabetes, while adjusting for onychomycosis treatments, co-morbidities, and demographic characteristics. Time-varying covariates were used to account for diagnosis timing. Results: 112,204 insured patients met the inclusion criteria and were followed for 19.3 years on average. Onychomycosis was diagnosed among 68,201 (60.8 %) patients and was found to be associated with an increased risk for future diabetes diagnosis (HR = 2.21, 95 %CI: 2.11,2.32, p-value<0.0001). The hazard ratio progressively increased with the number of onychomycosis diagnoses. Onychomycosis treatment was found to be associated with a decreased risk for diabetes diagnosis. Conclusions: This study found that past onychomycosis diagnosis was associated with an increased risk for future diabetes. We thus call for laboratory investigation of the findings and their implications.