A daily low-dose supplement may double chemotherapy effectiveness, with 43% of women seeing their cancer completely disappear.
A common vitamin could quietly supercharge chemotherapy. In a small but striking study from Brazil, women with breast cancer who took a daily vitamin D supplement alongside their treatment were far more likely to see their cancer vanish than those who did not, with success rates improving by nearly 79%.
Researchers at the Botucatu School of Medicine at São Paulo State University (FMB-UNESP) found that a simple, affordable vitamin D supplement may help chemotherapy work better in women with breast cancer, potentially offering a more accessible option compared to certain expensive or hard-to-obtain drugs designed to enhance chemotherapy response.
Higher Rates of Cancer Disappearance
The study, published in the journal Nutrition and Cancer and funded by FAPESP, included 80 women over the age of 45 who were preparing to begin neoadjuvant chemotherapy — treatment given before surgery to shrink tumors and make them easier to remove.
Participants were split into two equal groups. One group received a daily dose of 2,000 IU (international units) of vitamin D, while the other group was given placebo tablets.
After six months, the difference was notable. Among those taking vitamin D, 43% experienced complete disappearance of their cancer following chemotherapy. In comparison, only 24% of those in the placebo group saw the same result — meaning vitamin D boosted breast cancer treatment success by approximately 79%.
“Even with a small sample of participants, it was possible to observe a significant difference in the response to chemotherapy,” says Eduardo Carvalho-Pessoa, president of the São Paulo Regional Brazilian Society of Mastology and one of the study’s authors. “In addition, the dosage used in the research [2,000 IU per day] is far below the target dose for correcting vitamin D deficiency, which is usually 50,000 IU per week.”
Vitamin D’s Role in Immunity and Health
Vitamin D is best known for helping the body absorb calcium and phosphorus, which are critical for maintaining strong bones. However, growing evidence shows it also plays a role in immune function, helping the body defend against infections and diseases — including cancer. Since many patients are deficient, the vitamin could be playing a bigger role than expected.
The body produces vitamin D mainly through sunlight exposure, and it can also be obtained through certain foods. Current guidelines recommend 600 IU per day for most adults and 800 IU for older individuals. Excessive intake can be harmful and may lead to symptoms such as vomiting, weakness, bone pain, and kidney stones.
At the start of the study, most participants had low vitamin D levels, defined as less than 20 nanograms per milliliter (ng/mL) of blood. The Brazilian Society of Rheumatology recommends maintaining levels between 40 and 70 ng/mL.
“With supplementation, levels increased throughout chemotherapy treatment, which reinforces a possible contribution to the patients’ recovery,” Carvalho-Pessoa told Agência FAPESP. “Vitamin D is an accessible and inexpensive option compared to other drugs used to improve the response to chemotherapy, some of which are not even included in the list of the Unified Health System.”
Promising Results, More Research Needed
The findings point to a possible supportive role for vitamin D in cancer treatment, but researchers caution that more data is needed. Larger studies will help confirm how effective the supplement is and clarify how it influences chemotherapy response.
“These are encouraging results that justify a new round of studies with a larger number of participants,” Carvalho-Pessoa concludes. “This will allow a greater understanding of the role of vitamin D in increasing the response to chemotherapy treatment and, consequently, in the greater likelihood of breast cancer remission.”
Scientists say this affordable approach — a daily vitamin D supplement costing pennies per day — deserves much deeper investigation.
Journal Reference:
Omodei, M. S., et al. (2025). Vitamin D Supplementation Improves Pathological Complete Response in Breast Cancer Patients Undergoing Neoadjuvant Chemotherapy: A Randomized Clinical Trial. Nutrition and Cancer, 77(6), 648. DOI: 10.1080/01635581.2025.2480854