Study Reveals Low-Dose Vitamin D Enhances Chemotherapy Efficacy in Breast Cancer

A recent study conducted at the Botucatu School of Medicine, São Paulo State University (FMB-UNESP) in Brazil, has demonstrated that low-dose vitamin D supplementation can significantly enhance the effectiveness of chemotherapy in women diagnosed with breast cancer. The research, which was supported by the São Paulo Research Foundation (FAPESP), involved a cohort of 80 women aged over 45 who were initiating chemotherapy at the oncology outpatient clinic of Hospital das Clínicas at FMB-UNESP.

Participants were divided into two groups; one group received a daily supplement of 2,000 IU of vitamin D, while the other was administered placebo tablets. After six months of treatment, 43% of women in the vitamin D group achieved a complete pathological response to chemotherapy—meaning their disease was undetectable—compared to only 24% in the placebo group. This stark contrast indicates a potential role for vitamin D as a low-cost adjunct therapy to enhance chemotherapy responses, particularly in patients with low baseline vitamin D levels, which were defined as less than 20 ng/mL in the study.

Dr. Eduardo Carvalho-Pessoa, the president of the São Paulo Regional Brazilian Society of Mastology and one of the authors of the study published in the journal *Nutrition and Cancer*, emphasized that even though the sample size was modest, the findings were statistically significant. He noted that the daily dosage used in the research is substantially lower than the commonly recommended doses for correcting vitamin D deficiency, which can be as high as 50,000 IU per week.

The broader implications of this study are profound, as vitamin D is not only essential for bone health due to its role in calcium and phosphorus absorption, but it is also increasingly recognized for its immunological functions. Recent literature suggests that vitamin D may bolster immune responses against various diseases, including cancer. Nonetheless, it is crucial to highlight that excessive vitamin D intake can lead to toxicity, presenting risks such as nausea, weakness, and kidney stones.

According to the Brazilian Society of Rheumatology, optimal vitamin D levels should range between 40 and 70 ng/mL. The supplementation used in the study effectively elevated the vitamin D levels in participants throughout their chemotherapy treatment, potentially aiding their recovery.

The findings of this study have sparked interest in further research to explore the role of vitamin D in cancer treatment. Dr. Carvalho-Pessoa stated, "These encouraging results justify a new round of studies with larger participant numbers to deepen our understanding of vitamin D's contribution to chemotherapy efficacy and its potential to increase breast cancer remission rates."

As the medical community continues to seek innovative and accessible treatments for cancer patients, these findings regarding low-dose vitamin D supplementation may pave the way for new therapeutic strategies that are both effective and economically viable. The ongoing investigation into the relationship between vitamin D levels and cancer treatment responses promises to enhance patient care and outcomes in oncology.

The study, titled "Vitamin D Supplementation Improves Pathological Complete Response in Breast Cancer Patients Undergoing Neoadjuvant Chemotherapy: A Randomized Clinical Trial," was co-authored by M.S. Omodei et al. and published in *Nutrition and Cancer* in 2025. The study highlights the critical need for ongoing research into adjunct therapies that can improve patient outcomes in breast cancer treatment and underscores the importance of monitoring and managing vitamin D levels in patients undergoing chemotherapy.