Researchers at a Brazilian medical university have identified a striking connection between vitamin D supplementation and chemotherapy effectiveness in breast cancer patients, with new data showing nearly double the complete cancer disappearance rates compared to placebo.
The study, conducted at the Botucatu School of Medicine at São Paulo State University, enrolled 80 women over 45 who were beginning neoadjuvant chemotherapy, a pre-surgical treatment designed to shrink tumors. Half received a daily 2,000 IU vitamin D supplement while the other half got placebo pills.
After six months of treatment, the results diverged sharply. Among women taking vitamin D, 43% experienced complete disappearance of their cancer. In the placebo group, only 24% achieved the same outcome, nearly a 79% relative improvement in response rates.
What makes the finding particularly striking is the dose. The 2,000 IU daily amount falls well below standard vitamin D deficiency correction protocols, which typically involve 50,000 IU weekly. Most study participants began with deficient vitamin D levels, below 20 nanograms per milliliter of blood.
Eduardo Carvalho-Pessoa, a study author and president of the São Paulo Regional Brazilian Society of Mastology, emphasized the practical implications. "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," he said, referring to Brazil's public health network.
Vitamin D's immune-boosting properties have long intrigued cancer researchers. While the vitamin is best known for enabling calcium and phosphorus absorption for bone health, mounting evidence suggests it plays a crucial role in immune function, helping the body fight infections and diseases including cancer. The body produces vitamin D through sunlight exposure and can obtain it from certain foods.
Current guidelines recommend 600 IU daily for most adults and 800 IU for seniors. The American Academy of Pediatrics advises 400 IU for infants. Excessive intake carries risks, potentially causing vomiting, weakness, bone pain, and kidney stones.
The Brazilian Society of Rheumatology recommends maintaining blood levels between 40 and 70 nanograms per milliliter. During the trial, vitamin D supplementation increased participants' levels throughout chemotherapy, which researchers believe contributed to improved treatment response.
The research team acknowledged the study's modest size and called for larger trials to confirm the findings and better understand the mechanism behind vitamin D's apparent chemotherapy-enhancing effect. "These are encouraging results that justify a new round of studies with a larger number of participants," Carvalho-Pessoa said. "This will allow a greater understanding of the role of vitamin D in increasing the response to chemotherapy treatment."
The findings were published in the journal Nutrition and Cancer in 2025 and were funded by FAPESP, a Brazilian research foundation.
Author Jessica Williams: "A cheap supplement doubling cancer remission rates would be a game-changer if these results hold up in larger studies, but we're not there yet."
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