New research from São Paulo State University in Brazil suggests that a simple and affordable supplement—vitamin D—could help improve the effectiveness of chemotherapy in women with breast cancer.
The study, carried out at the Botucatu School of Medicine (FMB-UNESP), found that women who took a low daily dose of vitamin D during chemotherapy were more likely to see their tumors disappear compared to those who took a placebo.
The clinical trial involved 80 women over the age of 45 who were about to begin chemotherapy at a public hospital in Brazil. All of them received neoadjuvant chemotherapy, a type of treatment given before surgery to shrink the tumor and make it easier to remove.
The women were split into two groups: one group received 2,000 international units (IU) of vitamin D daily, while the other received a placebo. This dosage is considered relatively low, especially compared to doses used for correcting vitamin D deficiency.
After six months of treatment, the results were promising. In the vitamin D group, 43% of women experienced what doctors call a “complete pathological response”—meaning their cancer disappeared after chemotherapy.
In the placebo group, only 24% of women saw the same result. Despite the small number of participants, the difference was significant enough to suggest that vitamin D could play a helpful role in cancer care.
One of the study’s authors, Dr. Eduardo Carvalho-Pessoa, noted that this dose—2,000 IU per day—is much lower than the typical 50,000 IU per week used to treat vitamin D deficiency.
He emphasized that the supplement could offer a low-cost and more accessible option for improving treatment outcomes, especially compared to expensive drugs designed to enhance chemotherapy that are often out of reach for public healthcare systems.
Vitamin D is best known for helping the body absorb calcium and phosphorus, which are vital for bone health. But in recent years, scientists have also discovered its important role in supporting the immune system.
This includes helping the body fight off infections and, potentially, slowing the growth of cancer cells. Most studies linking vitamin D and cancer have used high doses, but this research suggests even small doses might offer benefits.
Vitamin D is mostly produced when the skin is exposed to sunlight, but it can also be obtained from foods like fish, eggs, and fortified dairy products. The recommended daily intake is 600 IU for adults, or 800 IU for older adults. Babies are advised to get 400 IU per day. Taking too much can be harmful, though, and may lead to side effects like nausea, bone pain, or kidney stones.
Many women in the study started with low vitamin D levels, which were defined as less than 20 nanograms per milliliter of blood. According to the Brazilian Society of Rheumatology, healthy levels should be between 40 and 70 ng/mL.
The researchers found that vitamin D levels rose over the course of the treatment among women in the supplement group, which may have helped improve their response to chemotherapy.
Dr. Carvalho-Pessoa highlighted that vitamin D is both inexpensive and widely available—making it an attractive candidate for further research in cancer care, especially in countries with limited access to high-cost medications. He believes the study lays the groundwork for larger trials.
“These are encouraging results that justify a new round of studies with more participants,” he said. “That will help us better understand how vitamin D may support chemotherapy and improve the chances of breast cancer remission.”
In summary, this small but important study points to the possibility that a low daily dose of vitamin D could help breast cancer patients respond better to chemotherapy—offering hope for a simple, affordable way to support cancer treatment.
If you care about breast cancer, please read studies about a major cause of deadly breast cancer, and this daily vitamin is critical to cancer prevention.
For more information about cancer, please see recent studies that new cancer treatment could reawaken the immune system, and results showing vitamin D can cut cancer death risk.
The research findings can be found in Nutrition and Cancer.
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