Vitamin D and Uterine Fibroid Growth, Incidence, and Loss: a Prospective Ultrasound Study

Objective: Fibroid treatments that have few side-effects and can preserve fertility are a clinical priority. We studied the association between serum vitamin D and uterine fibroid growth, incidence, and loss.

Design: A prospective community cohort study (enrollment 2010-2012) with 4 study visits over 5 years to conduct standardized ultrasounds, measure 25-hydroxyvitamin D (25(OH)D), and update covariates.

Setting: Detroit, Michigan area.

Patients: Self-identified African American or Black women aged 23-35 at enrollment without previous clinical diagnosis of fibroids.

Intervention(s): Serum 25(OH)D measured using immunoassay or liquid chromatography-tandem mass spectrometry.

Main Outcome Measure(s): The primary outcomes were fibroid growth, as measured by change in log volume per 18 months, and fibroid incidence (first detection of fibroid in previously fibroid-free uterus). Adjusted growth estimates from linear mixed models were converted to estimated difference in volume for high vs. low 25(OH)D. Incidence differences were estimated as hazard ratios from age-specific Cox regression. A secondary outcome fibroid loss (reduction in fibroid number between visits), was modeled using Poisson regression. Covariates (reproductive and hormonal variables, demographics, body mass index, current smoking) and 25(OH)D were modeled as time-varying factors.

Result(s): At enrollment among 1,610 participants with ≥1 follow-up ultrasound, mean age was 29.2 years, 73% had deficient vitamin D (<20ng/mL), and only 7% had sufficient vitamin D (≥30ng/mL). Serum 25(OH)D ≥20ng/mL compared with <20ng/mL was associated with an estimated 9.7% reduction in fibroid growth (95% confidence interval [CI]: -17.3%, -1.3%), similar to the minimally adjusted estimate -8.4% (95% CI: -16.4, 0.3). Serum 25(OH)D ≥30ng/mL compared with <30ng/mL was associated with an imprecise 22% reduction in incidence (adjusted hazard ratio=0.78; 95% CI: 0.47, 1.30), similar to the unadjusted estimate of 0.84 (95% CI: 0.51, 1.39). The >30ng/mL group also had a 32% increase in fibroid loss (adjusted risk ratio=1.32; 95% CI: 0.95, 1.83).

Conclusion(s): Our data support the hypothesis that high concentrations of vitamin D decrease fibroid development but are limited by the few participants with serum 25(OH)D ≥30ng/mL. Interventional trials that raise and maintain 25(OH)D concentrations >30ng/mL and then prospectively monitor fibroid development are needed to further assess supplemental vitamin D efficacy and determine optimal treatment protocols.