A recent clinical trial found that taking a daily dose of vitamin D during chemotherapy may significantly improve treatment outcomes for women with breast cancer.
Study design
The randomized trial enrolled 80 women aged 45 and older who were diagnosed with breast cancer and scheduled to receive neoadjuvant chemotherapy, which is chemotherapy given before surgery to shrink tumors. Half of the participants took 2,000 IU of vitamin D each day for six months while undergoing treatment. The other half took a placebo.
Vitamin D is known for its role in bone health, but it also influences the immune system and cellular processes linked to cancer. Breast tissue contains vitamin D receptors. When activated, these receptors can slow tumor growth and promote cancer cell death.
Key findings
After completing chemotherapy and surgery, 43 percent of women who took vitamin D had a pathological complete response, meaning no cancer was detectable in their breast tissue. Only 24 percent of women in the placebo group achieved that result. This represents a near-doubling in the rate of tumor eradication before surgery.
The researchers also measured blood levels of vitamin D. Women with levels above 20 nanograms per milliliter were more than three times as likely to reach a complete tumor response, regardless of other clinical factors. This suggests that even moderate vitamin D sufficiency may enhance the effectiveness of chemotherapy.
Possible reasons for the effect
Vitamin D influences genes that control cell growth, programmed cell death, and the spread of tumors. It may also improve how cancer cells respond to common chemotherapy drugs such as anthracyclines and taxanes. Previous studies have shown that vitamin D can increase the sensitivity of cancer cells to these drugs and boost their tumor-killing effects.
Many breast cancer patients, especially postmenopausal women, have low vitamin D levels at the time of diagnosis. This deficiency may impair how well the body responds to treatment. Chemotherapy itself can lower vitamin D levels by reducing sun exposure and affecting metabolism. Taking a supplement during treatment may help counter that decline.
What this means for patients
Supplementing with a safe, accessible dose of 2,000 IU of vitamin D daily during chemotherapy could be a simple strategy to improve treatment outcomes. The study was relatively small and conducted at a single center, but its randomized design strengthens the evidence that vitamin D supplementation may help breast cancer patients achieve better tumor control.
More research is needed to confirm these findings in larger and more diverse populations and to identify the best dosing. Given the low cost, safety at recommended doses, and potential benefits, vitamin D supplementation may be a practical addition to breast cancer treatment for patients with low blood levels.
The findings were published in the journal Nutrition and Cancer.
