Differences in 25-hydroxy vitamin D and vitamin D-binding protein concentrations according to the severity of endometriosis

Objective: To investigate serum 25-hydroxyl vitamin D (25(OH) D) and vitamin D-binding protein (VDBP) concentrations in women with endometriosis according to the severity of disease. Methods: Women with mild endometriosis (n=9) and advanced endometriosis (n=7), as well as healthy controls (n=16), were enrolled in this observational study. Serum total 25(OH) D concentrations were analyzed using the Elecsys vitamin D total kit with the Cobas e602 module. Concentrations of bioavailable and free 25(OH) D were calculated. Concentrations of VDBP were measured using the Human Vitamin D BP Quantikine ELISA kit. Variables were tested for normality and homoscedasticity using the Shapiro-Wilk test and Leven F test, respectively. Correlation analysis was used to identify the variables related to total 25(OH) D and VDBP levels. To assess the effects of total 25(OH) D and VDBP levels in the three groups, multivariate generalized additive modeling (GAM) was performed. Results: Gravidity and parity were significantly different across the three groups. Erythrocyte sedimentation rate (ESR) and CA-125 levels increased as a function of endometriosis severity, respectively (p=0.051, p=0.004). The correlation analysis showed that total 25(OH) D levels were positively correlated with gravidity (r=0.59, p<0.001) and parity (r=0.51, p<0.003). Multivariate GAM showed no significant relationship of total 25(OH) D levels with EMT severity after adjusting for gravidity and ESR. However, the coefficient of total 25(OH) D levels with gravidity was significant (1.87; 95% confidence interval, 0.12-3.63; p=0.040). Conclusion: These results indicate that vitamin D and VDBP levels were not associated with the severity of endometriosis.