In June 2025, a randomized clinical trial conducted at the Botucatu Medical School (FMB‑UNESP) in Brazil revealed that daily supplementation with 2,000 IU of vitamin D for six months during neoadjuvant chemotherapy significantly increased the pathological complete response (pCR): 43% of patients achieved pCR, compared to 24% in the placebo group (p = 0.04). This finding represents a relative response improvement of nearly 79%, a key figure that is reshaping expectations in oncology.

The study involved 80 women over the age of 45 diagnosed with breast cancer; 75 completed the protocol with conclusive results. At the start, both cohorts showed average 25‑hydroxyvitamin D levels of 19–21 ng/mL, indicating deficiency. After the intervention, the supplemented group reached average levels of 28 ng/mL, significantly higher than the 20 ng/mL in the placebo group (p = 0.03).

The adjusted logistic regression analysis indicated that having levels ≥20 ng/mL increased the likelihood of achieving pCR by 3.65 times (95% CI: 1.09–12.8; p = 0.04). Moreover, recent complementary studies published in journals such as World Journal of Surgery and Cancer Research have reinforced this approach, showing a clear statistical association between supplementation and improved treatment response.

Vitamin D, beyond its classical roles (mineral absorption, immune function), appears to enhance chemotherapy-induced cell death by inhibiting tumor proliferation, angiogenesis, and invasion. The National Cancer Institute also supports these biological mechanisms, although until now, no clinical trials had shown such strong evidence.

However, it is important to maintain a balanced perspective. Large-scale studies such as VITAL and WHI, aimed at prevention, did not find significant reductions in cancer incidence or mortality with routine supplementation. Therefore, these results should be considered emerging evidence in a therapeutic context, not a preventive cure.

Conclusion

The Brazilian study brings strong hope for the use of vitamin D as an adjuvant in breast cancer treatment, highlighting a dramatic improvement in response to chemotherapy. However, it is essential to continue with larger trials and long-term follow-up, to assess safety (toxic levels, hyperparathyroidism), and to determine whether these improvements translate into greater overall survival. What is clear is that, based on current data, the “sunshine vitamin” stands out as a promising and accessible tool to strengthen breast cancer care strategies