Effect of Vitamin D Supplementation on Risk of Breast Cancer: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Study answer

What this study found

Vitamin D3 supplementation did not significantly reduce breast cancer risk or affect mammographic density. Across 7 RCTs (19,137 women), the pooled risk ratio for breast cancer was 1.04 (95% CI 0.84–1.28; P = 0.71). For mammographic density, data from 3 trials (584 participants) showed no significant change (mean difference 0.46; 95% CI −2.06 to 2.98; P = 0.72). Bayesian analyses remained non-significant across prior assumptions. There is insufficient evidence to support the efficacy of vitamin D supplementation for breast cancer risk reduction or mammographic density changes; observational…

Study & population

Parallel randomized controlled trials enrolling adult female participants (≥18 years) from North America and Europe; included premenopausal and postmenopausal women; comparisons against placebo; some trials allowed cointerventions such as calcium or omega-3 fatty acids.

Intervention

Vitamin D3 (cholecalciferol) supplementation regimens varied across trials: daily doses from 400 to 3,000 IU/day (examples include 800, 1,100, 2,000, and 3,000 IU/day); intermittent high-dose regimens included 100,000 IU every 3 months and 200,000 IU loading followed by 100,000 IU monthly; some arms combined vitamin…

Key limitation

Some trials had risk of bias (incomplete outcomes, loss to follow-up); several studies had short follow-up (<12 months); substantial heterogeneity for mammographic density; results dominated by two large trials; trials conducted in developed countries only; limited data on cancer subtypes and long-term safety at…

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Original abstract