A recent clinical trial found that breast cancer patients who took a daily vitamin D supplement during chemotherapy were nearly twice as likely to have no detectable cancer remaining after surgery, compared to those who took a placebo. The study, published in a peer-reviewed journal, adds to evidence that vitamin D may boost the effectiveness of standard cancer treatment.
The trial enrolled 80 women aged 45 and older who had been diagnosed with breast cancer and were about to start neoadjuvant chemotherapy, a type of chemotherapy given before surgery to shrink tumors. Participants were randomly assigned to receive either 2,000 IU of vitamin D daily or a placebo for six months, covering the duration of their chemotherapy treatment.
After completing chemotherapy and undergoing surgery, 43 percent of women who took vitamin D achieved a pathological complete response, meaning no cancer cells were found in the breast tissue. In the placebo group, only 24 percent reached that outcome. The difference represents a near doubling in the rate of tumor eradication before surgery.
Researchers also measured blood levels of vitamin D to assess each participant’s vitamin D status. Women with levels above 20 nanograms per milliliter were more than three times as likely to achieve a complete tumor response, regardless of other clinical factors. This suggests that even moderate vitamin D sufficiency may help chemotherapy work better.
Vitamin D is known to influence genes involved in cell growth, programmed cell death, and the spread of tumors. It can also increase how sensitive cancer cells are to chemotherapy drugs such as anthracyclines and taxanes, which are commonly used in breast cancer treatment. Previous studies have shown that vitamin D can promote the tumor-killing effects of these drugs.
Many breast cancer patients, especially postmenopausal women, have low vitamin D levels at the time of diagnosis. Chemotherapy itself can further reduce vitamin D levels because patients often have less sun exposure and the drugs affect vitamin D metabolism. Supplementing with a moderate dose during treatment may help counter that decline.
The trial was relatively small and conducted at a single center, but its randomized design strengthens the evidence. Researchers say more studies are needed to confirm the findings in larger and more diverse populations and to explore the best dose. Vitamin D is affordable and safe at the dose used in this study, which makes it a practical option for patients who have low levels.
This study adds to a growing body of research linking nutrient status to cancer outcomes. Maintaining adequate vitamin D levels may be a low-risk way to support more successful breast cancer treatment, beyond its well-known role in bone health.
