Scientists in Brazil have found that a simple daily vitamin D supplement may help chemotherapy work more effectively in women with breast cancer and provide an affordable, simple option to enhance chemo treatment.
In a small study, published in Nutrition and Cancer, women who took low doses alongside treatment were far likelier to see their cancer vanish than those who didn’t. Since vitamin D also supports immune function – and many patients are deficient – it could be playing a bigger role than expected, they said, adding that this affordable approach deserves much deeper investigation.
The study, carried out at the Botucatu School of Medicine at São Paulo State University (FMB-UNESP), suggests that low doses of the vitamin could improve treatment outcomes and potentially serve as a more accessible option than certain expensive or hard-to-obtain drugs designed to boost chemotherapy response.
The research, funded by the São Paulo Research Foundation (FAPESP), included 80 women over 45 who were preparing to begin treatment at the oncology outpatient clinic of the general and teaching hospital (Hospital das Clínicas) at FMB-UNESP.
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.
All of the women underwent neoadjuvant chemotherapy, a treatment given before surgery to shrink tumours and make them easier to remove.
Higher rates of cancer disappearance
After six months, the difference between the two groups was notable. Among those taking vitamin D, 43% experienced complete disappearance of their cancer after chemotherapy. In comparison, only 24% of those in the placebo group saw the same result.
“Even with a small sample of participants, it was possible to observe a significant difference in the response to chemotherapy. 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,” said Eduardo Carvalho-Pessoa, president of the São Paulo Regional Brazilian Society of Mastology and one of the study’s authors.
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.
Many previous studies examining vitamin D and cancer have focused on much higher doses than those used in this research.
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. The American Academy of Paediatrics advises 400 IU daily for infants.
Excessive intake can be harmful and may lead to symptoms such as vomiting, weakness, bone pain and kidney stones.
Low levels and treatment response
At the start of the study, most participants had low vitamin D levels, defined as less than 20 nanograms per millilitre (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 said. “Vitamin D is an accessible and inexpensive option compared with other drugs used to improve the response to chemotherapy, some of which are not even included in the list of the Unified Health System,” he adds. (The United Health System is the Brazilian national public health network, known as the SUS – its acronym in Portuguese).
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 are 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. 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,” he said.
Study details
Vitamin D Supplementation Improves Pathological Complete Response in Breast Cancer Patients Undergoing Neoadjuvant Chemotherapy: A Randomised Clinical Trial
Michelle Sako Omodei, Jackeline Chimicoviaki, Daniel Araujo Brito Buttros et al.
Published in Nutrition and Cancer on 17 March 2025
Abstract
This study aimed to evaluate the effect of vitamin D (VD) supplementation on the pathological complete response (pCR) rate in women with breast cancer (BC) undergoing neoadjuvant chemotherapy (NCT). A randomised clinical trial was conducted with 80 women aged ≥45years with BC who were eligible for NCT. Women were randomised into two groups: VD group, daily supplementation with 2,000IU of cholecalciferol (n = 40) or placebo (n = 40), for 6 months. The primary outcome measure was the pCR rate. Serum 25-hydroxyvitamin-D [25(OH)D] levels were measured after BC diagnosis and the end of NCT. Of the 80 randomised women, 75 completed the NCT and underwent surgery. Baseline 25(OH)D values indicated hypovitaminosis D in both groups (VD: 19.6 ± 5.8 ng/mL and placebo: 21 ± 7.9 ng/mL, p = 0.33). After 6 months, 25(OH)D levels increased in the VD group compared to the placebo group (28 ± 8.7 vs. 20.2 ± 6.1 ng/mL, p = 0.03). The pCR rate was higher in women supplemented with VD when compared than the placebo (43% vs. 24%, p = 0.04). Adjusted logistic regression showed that women with 25(OH)D levels ≥20ng/mL were more likely to achieve pCR (OR3.65, 95%CI 1.09-12.8, p = 0.04). Women with BC undergoing NCT who received supplementation with 2,000IU of VD were more likely to achieve a pathological complete response than women in the placebo group.
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