April 28, 2026 — Researchers at the Botucatu School of Medicine, São Paulo State University (FMB-UNESP) in Brazil, have published striking results from a clinical trial showing that a daily low-dose vitamin D supplement significantly improves chemotherapy outcomes in breast cancer patients. The study found that 43% of patients taking vitamin D achieved complete tumor disappearance after chemotherapy, compared to only 24% in the placebo group.

Study Design

The FAPESP-funded study enrolled 80 women over the age of 45 who were preparing to receive neoadjuvant chemotherapy (pre-surgical treatment designed to shrink tumors for easier surgical removal) at the oncology outpatient clinic of the university’s teaching hospital.

Participants were randomly divided into two groups: the experimental group received a daily dose of 2,000 IU (international units) of vitamin D, while the control group received placebo tablets. All patients underwent standard neoadjuvant chemotherapy regimens.

Key Findings

After six months of treatment, a notable difference emerged between the two groups:

• Vitamin D group: 43% of patients achieved pathological complete response (pCR) — complete tumor disappearance following chemotherapy.
• Placebo group: Only 24% achieved the same result.

“Despite the small sample size, this result is encouraging,” said one of the study’s lead researchers. “Vitamin D, as an inexpensive and widely available supplement, could have a profound impact on global breast cancer treatment if validated in larger clinical trials.”

Scientific Mechanism

Researchers hypothesize that vitamin D may enhance chemotherapy effectiveness through multiple mechanisms. First, vitamin D plays an important role in immune modulation, and many cancer patients are deficient in the vitamin. Second, vitamin D has been shown to influence cancer cell growth and differentiation processes, potentially making cancer cells more sensitive to chemotherapy drugs.

Caution and Outlook

The research team emphasized the limitations of their findings. Due to the small sample size, these results need to be validated in larger, multi-center clinical trials. Additionally, it remains unclear what the optimal dosage, timing, and which patient subgroups would benefit most.

Nevertheless, given the low cost and high safety profile of vitamin D supplements, this study offers a highly promising avenue for improving breast cancer treatment outcomes.

Source: ScienceDaily