# Vitamin D Supplementation and Testosterone Levels in Breast Cancer Survivors

## TL;DR

This study found that vitamin D supplementation does not significantly affect testosterone levels in breast cancer survivors over two years.

## Contribution

The study provides evidence that vitamin D supplementation does not adversely impact testosterone levels in breast cancer survivors.

## Key findings

- Vitamin D supplementation did not significantly alter testosterone levels in breast cancer survivors over 24 months.
- Baseline testosterone levels were the most significant predictor of testosterone trajectories.
- The results suggest vitamin D supplementation is safe regarding testosterone modulation in this population.

## Abstract

Vitamin D plays a key role in immune modulation, cell proliferation, and hormone regulation. Dysregulated testosterone may contribute to breast cancer progression. We investigated whether long-term vitamin D supplementation affects serum testosterone levels in breast cancer survivors. Complete data at baseline, 12, and 24 months were derived from 253 women with early-stage breast cancer participating in the DEDiCa trial and randomized to receive either a high-dose vitamin D to maintain serum 25(OH)D at 60 ng/mL (group A) or a standard dose to maintain serum levels at 30 ng/mL (group B). Serum 25(OH)D levels significantly increased in both groups (p < 0.001). No significant changes in testosterone concentrations were observed between treatment groups over the 24 month treatment period (A: 0.125 to 0.140 ng/mL; B: 0.162 to 0.193 ng/mL; p = 0.682). Baseline serum testosterone levels emerged as the most significant predictor of testosterone trajectories, possibly modulated by hormone-suppressive therapy. These results are reassuring that vitamin D supplementation did not adversely affect testosterone levels in this population of breast cancer survivors and may partially concur with a healthy lifestyle to equilibrate testosterone levels.