23/06/2026
Yet another reason to optimise your vitamin D intake.
A remarkable series of recently published papers has thrust vitamin D status and supplementation into the spotlight as a potentially important modifier of breast cancer treatment outcomes, with converging evidence linking vitamin D status to treatment response, survivorship trajectories and the severity of treatment-related toxicity.
Over the next two postings I will be outlining these important new developments.
A major emerging theme is the relationship between vitamin D and response to neoadjuvant chemotherapy (NACT). NACT refers to chemotherapy given before the main definitive treatment for a cancer, usually surgery. In breast cancer, it is commonly used to shrink the tumour prior to surgical removal.
Two randomised clinical trials published in 2025 found that vitamin D supplementation during NACT significantly increased pathological complete response (pCR) rates. In one study of 80 women with breast cancer, daily supplementation with 2,000 IU cholecalciferol increased pCR rates from 24% in the placebo group to 43% in the vitamin D group, with women achieving serum 25(OH)D levels ≥20 ng/mL (≥50 nmol/L) showing markedly higher odds of pCR (OR 3.65). Another larger randomised trial involving 227 patients used weekly 50,000 IU vitamin D3 during NACT and similarly found vitamin D supplementation independently predicted pCR (OR 2.33). Importantly, these benefits appeared strongest in biologically aggressive tumors, particularly HER2-positive and hormone receptor-negative disease.
These individual trials are reinforced by a 2026 systematic review and meta-analysis pooling all available randomised studies (n=338). The meta-analysis reported that vitamin D supplementation approximately doubled the likelihood of achieving pCR (RR 2.09) with remarkably low heterogeneity (I²=0%), suggesting a highly consistent signal across studies. Residual tumour burden was also significantly reduced. Collectively, these studies support the concept that vitamin D may enhance chemotherapy responsiveness, potentially through immunomodulatory, anti-proliferative and differentiation-promoting mechanisms mediated through the vitamin D receptor (VDR).
For more information see:
https://pubmed.ncbi.nlm.nih.gov/40098326/
https://pubmed.ncbi.nlm.nih.gov/40229998/
https://pubmed.ncbi.nlm.nih.gov/42061434/
