Standard-dose Vitamin D supplementation as an effective and safe non-hormonal treatment for the prevention of uterine fibroid growth in reproductive-age women: A pilot study

Abstract Study question Could low-dose vitamin D supplementation prevent uterine fibroid growth in reproductive-age women with hypovitaminosis D? Summary answer Six-month low-dose Vitamin D supplementation (≈ 1500 IU/day) in patients with hypovitaminosis D significantly decrease uterine fibroid growth compared to patients not receiving supplementation. What is known already Uterine fibroids (UF) are the most common tumor of the reproductive tract, affecting up to 77% of reproductive-age women. Due to the association between hypovitaminosis D and UF, several studies have evaluated the effect of a high Vitamin D (VitD) dose (3500-8500 IU/day) on UF size, proposing VitD supplementation as a therapeutic option. However, the standard dose recommended for VitD deficiency (800-2000 IU/day) has not been assessed. We aimed to evaluate if the restoration of normal serum levels of 25(OH)D by standard VitD dose in patients with UF and hypovitaminosis D can avoid the growth of UF in reproductive-age women. Study design, size, duration Ambispective observational study carried out at La Fe University Hospital. In the study group, patients (n = 6) were prospectively recruited from 2019 to 2022. Clinical data from the control group (n = 14) was collected retrospectively from 2016 to 2018. The study was approved by the autonomous government ethics committee (CAEPO; Spain) (ISS-COL-2028-01). Participants/materials, setting, methods Twenty women under 45 years old with uterine fibroids and hypovitaminosis D [25(OH)D levels < 30 ng/mL] were included. The study group received VitD for 6 months (25000 IU/2 weeks). Study outcomes: UF size determined by ultrasound, serum levels of 25(OH)D, Calcium, AST, ALT, Bilirubin and Creatinine were determined at 0, 3 and 6 months. Data from control group was obtained retrospectively from patients diagnosed with UF and hypovitaminosis D without VitD supplementation. Main results and the role of chance At the beginning of the treatment, no significant differences were found between patients included in the control and VitD group regarding age (40.57 ± 2.76 vs. 38.73 ± 4.92), BMI (23.6 5 ± 2.96 vs. 25.36 ± 4.25), VitD levels (18.57 ± 7.47 vs. 23.37 ± 37.29) and UF size (67.07 ± 20.68 vs. 56.17 ± 12.56). After treatment, VitD levels significantly increased in the study group (23.37 ± 37.29 vs. 37.02 ± 6.35, p = 0.001). Regarding size, the control group showed a significant UF growth of 17.3 ± 14.31% (p = 0.0005) after 6 months, while in patients treated with VitD UF size slightly decreased (-5.84 ± 2.14 %, p = 0.15). In addition, when comparing % of UF growth in both groups at the end of the treatment, UF growth was significantly lower in patients treated with VitD compared to control (-5.84% vs. 17.3%, p = 0.0002). There were no significant changes in serum parameters analyzed in the study group after 6 months of VitD supplementation: Calcium (9.15 vs. 9.20 mg/dL), AST (15.83 vs. 13 U/L), ALT (17.83 vs. 16 U/L), Bilirubin (0.42 vs. 0.48 mg/dL) and Creatinine (0.69 vs. 0.67 mg/dL). Limitations, reasons for caution This is an observational study and thus possible confounders cannot be completely excluded. More data are needed to draw firm conclusions and it will be critical to increase the sample size to check if the results observed in this work remain in the general population. Wider implications of the findings To our knowledge, this is the first study evaluating the effect of standard VitD dose on UF growth in reproductive-age women with hypovitaminosis D. Our results suggest that low-dose VitD could be a safe non-hormonal therapeutic option in the management of UF in patients willing to preserve their fertility. Trial registration number NCT03991078