The effect of vitamin D on recurrence of uterine fibroids: A randomized, double-blind, placebo-controlled pilot study

Background: and purpose: A deficiency of vitamin D has been suggested as one of the principal risk factors for uterine fibroids (UFs). We aimed to investigate the effect of vitamin D supplementation on the recurrence of UFs. Materials and methods: In a randomized, double-blind, placebo-controlled pilot study, women who had undergone hysteroscopic myomectomy from November 2017 to June 2020 were randomly given either vitamin D (1000 IU tablet; n = 55), or placebo (n = 54) daily for 12 months. Both groups were followed and compared in regard of the primary outcomes of the study, which were recurrence rates, size, and numbers of UFs based on three-dimensional transvaginal ultrasound investigation (3D-TVS). Data analysis was performed by the intention-to-treat (ITT) approach. Results: The mean age of the study participants was 37.9 +/- 6.5 years. The two groups did not differ significantly in terms of demographic and pre-intervention clinical characteristics. The administration of vitamin D supplements for one year reduced recurrence rates of UFs by 50% (p = 0.17). Vitamin D also reduced the size of recurrent UFs in the intervention group compared to controls (-7.7 mm), the difference was statistically different (p < 0.001). No adverse effect of vitamin D was reported in the present study. Conclusion: Based on these results, vitamin D appears to be a promising and safe agent in the prevention of recurrence and reduction of the size of recurrent UFs, although further well-designed and appropriately powered studies are required to demonstrate a significant difference in the size and number of recurrent UFs.