A recent clinical trial has found that taking a moderate daily dose of vitamin D may significantly improve the odds that chemotherapy will completely eliminate breast cancer tumors before surgery.
The study enrolled 80 women aged 45 and older with breast cancer who were about to receive neoadjuvant chemotherapy, a type of chemo given before surgery to shrink tumors. Participants were randomly assigned to take either 2,000 IU of vitamin D daily or a placebo for six months while undergoing chemotherapy.
After completing chemotherapy and surgery, 43% of the women who took vitamin D achieved a pathological complete response, meaning no detectable cancer remained in breast tissue. In the placebo group, only 24% reached that outcome. The researchers also measured blood levels of vitamin D. Women with levels above 20 ng/mL were more than three times as likely to achieve a complete tumor response, regardless of other clinical factors.
Vitamin D influences immune function and cellular processes involved in cancer progression. Breast tissue contains vitamin D receptors that, when activated, can slow tumor growth and promote cancer cell death. The vitamin also modulates genes related to cell proliferation, programmed cell death, and prevention of tumor spread. Previous research has shown that vitamin D increases cancer cell sensitivity to common chemotherapy drugs such as anthracyclines and taxanes.
Many breast cancer patients, especially postmenopausal women, have low vitamin D levels at diagnosis. Chemotherapy itself can further lower vitamin D levels by limiting sun exposure and affecting metabolism. The study suggests that supplementing with a safe, accessible dose of vitamin D during chemotherapy could be a simple strategy to improve treatment outcomes.
The trial was relatively small and conducted at a single center, but its randomized design strengthens the evidence. More research is needed to confirm the findings in diverse populations and to explore optimal dosing. Still, given the affordability and safety of vitamin D at recommended doses, maintaining adequate levels may be a practical addition to breast cancer treatment for patients with low levels.
The study was published in Nutrition and Cancer and can be accessed at https://www.tandfonline.com/doi/full/10.1080/01635581.2025.2480854.
