A new clinical trial suggests that taking a moderate daily dose of vitamin D during breast cancer treatment may improve the chance that chemotherapy eliminates tumors completely before surgery.
The study, published recently, enrolled 80 women aged 45 and older who had been diagnosed with breast cancer and were about to begin neoadjuvant chemotherapy. That is chemotherapy given before surgery to shrink tumors. The women were randomly assigned to take either 2,000 international units (IU) of vitamin D each day or a placebo for six months while they underwent treatment.
Vitamin D is known for its role in bone health, but it also affects the immune system and cellular processes linked to cancer. Breast tissue has vitamin D receptors. When activated, these receptors can slow tumor growth and promote the death of cancer cells.
After completing chemotherapy and surgery, 43 percent of the women who took vitamin D had a pathological complete response. That means no detectable cancer remained in the breast tissue. In the placebo group, only 24 percent reached that result. The rate of tumor eradication before surgery nearly doubled.
The researchers also measured vitamin D levels in the blood. Women with levels above 20 nanograms per milliliter were more than three times as likely to achieve a complete tumor response, regardless of other factors. This suggests that even moderate vitamin D sufficiency may help chemotherapy work better.
Vitamin D can affect genes involved in cell growth, programmed cell death, and the spread of tumors. It may also make cancer cells more responsive to common chemotherapy drugs such as anthracyclines and taxanes. Previous studies have shown that vitamin D increases cancer cell sensitivity to these drugs and amplifies their tumor-killing effects.
Many breast cancer patients, particularly those who have gone through menopause, are found to have low vitamin D levels at diagnosis. That deficiency could weaken the response to treatment. Chemotherapy itself can lower vitamin D levels because patients spend less time in the sun and because the drugs affect metabolism. Taking a supplement during treatment may help counter that drop.
According to the researchers, adding a safe and accessible dose of vitamin D, such as 2,000 IU per day, during chemotherapy could be a simple strategy to improve outcomes. The study was relatively small and conducted at a single center, but its randomized design adds weight to the findings. More research will be needed to confirm the results in larger and more diverse groups and to find the best dose.
Vitamin D supplements are affordable and safe at recommended levels. For breast cancer patients who have low vitamin D status, supplementation may offer a practical way to support treatment. The study provides further evidence that maintaining adequate vitamin D levels could be a low-risk step toward better cancer care.
