🟢 Strong Evidence
A randomized, placebo-controlled trial published in Nutrition and Cancer (PMID: 40098326) has found that vitamin D3 supplementation significantly improves treatment response in postmenopausal women with breast cancer receiving neoadjuvant chemotherapy. Women receiving 2,000 IU/day of vitamin D3 during a 6-month chemotherapy course achieved a 43% pathological complete response rate—defined as the absence of invasive cancer in both breast and axillary lymph nodes after surgery—compared to 24% in the placebo group.
Key takeaways
- Vitamin D3 supplementation at 2,000 IU/day nearly doubled pathological complete response rates (43% vs. 24%) in a randomized trial of 80 postmenopausal women with breast cancer
- Women with vitamin D levels of 25(OH)D ≥ 20 ng/mL were 3.65 times more likely to achieve complete response than those with deficient levels
- Baseline vitamin D deficiency was widespread in both groups (mean 19.6–21 ng/mL), suggesting a substantial proportion of the breast cancer population may benefit from supplementation
Study at a Glance
| Source | Nutrition and Cancer |
| Study type | Randomized, placebo-controlled trial |
| Sample size | N = 80 randomized; 75 completed treatment |
| Population | Postmenopausal women with breast cancer undergoing neoadjuvant chemotherapy |
| Intervention | Vitamin D3 2,000 IU/day vs. placebo for 6 months |
Vitamin D Status and Chemotherapy Response
Baseline and post-supplementation 25(OH)D levels, and odds of complete response by vitamin D threshold
Source: Nutrition and Cancer, 2025 (PMID: 40098326) | Georgian Medical Journal News
Widespread Vitamin D Deficiency in Breast Cancer Population
The trial revealed that baseline vitamin D deficiency was nearly universal among study participants. In the vitamin D group, baseline 25(OH)D levels averaged 19.6 ng/mL; in the placebo group, 21 ng/mL. Both values fall well below the 30 ng/mL threshold widely considered adequate for bone health and immune function, according to clinical guidelines published by the Endocrine Society.
Following supplementation, the vitamin D group’s levels rose significantly to 28 ng/mL, while the placebo group remained at 20.2 ng/mL. This 8 ng/mL gap proved clinically meaningful: logistic regression analysis showed that women with 25(OH)D ≥ 20 ng/mL were 3.65 times more likely to achieve pathological complete response than those with deficient levels. This finding suggests that correcting pre-existing vitamin D deficiency may represent a modifiable factor in breast cancer treatment outcomes. See related analysis on Clinical Updates for context on adjunctive therapies in oncology.
Proposed Mechanisms: How Vitamin D May Enhance Chemotherapy Efficacy
The authors propose several biological pathways through which vitamin D may sensitize tumor cells to chemotherapy. Vitamin D is known to promote apoptosis (programmed cell death) and cell cycle arrest in cancer cells, while increasing expression of tumor-suppressor genes. Additionally, vitamin D may reduce the metabolic stress that chemotherapy itself induces on cellular vitamin D stores, thereby maintaining adequate signaling throughout treatment.
The 2,000 IU/day dose was not arbitrary. Researchers selected this amount based on evidence that it can elevate 25(OH)D to ≥ 30 ng/mL in approximately 90% of the general population—a threshold hypothesized to improve cancer outcomes. However, the trial itself did not stratify participants by baseline vitamin D status, meaning some women entered the study with more pronounced deficiency than others, a limitation acknowledged by the authors.
Postmenopausal women receiving vitamin D3 2,000 IU/day achieved a 43% pathological complete response rate to neoadjuvant chemotherapy, compared to 24% in the placebo group—a finding consistent with emerging evidence that vitamin D status influences chemotherapy efficacy in breast cancer.
— Nutrition and Cancer (2025, PMID: 40098326)
Study Limitations and Clinical Translation
The trial’s relatively modest sample size (80 randomized, 75 completed) and single-center design mean that results require validation in larger, multi-center studies before influencing routine clinical practice. Additionally, the trial did not investigate potential interactions between vitamin D supplementation and specific chemotherapy regimens, nor did it examine whether vitamin D toxicity or hypercalcemia emerged at the 2,000 IU/day dose in this population. Because participants were postmenopausal women, results may not generalize to premenopausal or male patients with breast cancer.
Despite these limitations, the magnitude of the treatment effect—a 79% relative increase in complete response rate—warrants attention from oncologists and warrants investigation in prospective trials. The finding also aligns with broader evidence from observational studies suggesting that adequate vitamin D status is associated with better outcomes across multiple cancer types, though randomized evidence has been sparse until now. For further discussion of adjunctive micronutrient interventions in cancer, explore New Studies coverage at GMJ News.
What this means
Frequently asked questions
Should all breast cancer patients take vitamin D supplements?
Not necessarily. This trial was limited to postmenopausal women and showed a significant effect at 2,000 IU/day, but individual vitamin D status varies widely. A blood test measuring 25(OH)D is the first step; supplementation should be prescribed by your oncologist based on your baseline level and other health factors. Very high intakes can cause harm.
How long does it take for vitamin D supplementation to raise blood levels?
According to pharmacokinetic studies, 25(OH)D levels typically begin to rise within 1–2 weeks of daily supplementation, with stabilization occurring over 8–12 weeks. In this trial, supplementation occurred over 6 months during chemotherapy, allowing ample time for vitamin D status to normalize before treatment response was assessed.
What is a “pathological complete response” and why does it matter?
A pathological complete response (pCR) means that after surgery, pathologists find no invasive cancer remaining in the breast or lymph nodes—essentially, the tumor has been eradicated at the microscopic level. pCR is a strong prognostic indicator and is increasingly used as a primary endpoint in neoadjuvant trials because it correlates with long-term survival. Achieving pCR, when possible, is considered a major treatment success.
The findings from this Nutrition and Cancer trial suggest that vitamin D status is not a minor nutritional detail but a potentially modifiable variable in cancer treatment response. Larger randomized trials, particularly in diverse populations and across different cancer types, are now needed to confirm whether vitamin D supplementation should become part of standard neoadjuvant chemotherapy protocols for breast cancer and other malignancies.
Source: Vitamin D Supplementation and Pathological Complete Response in Neoadjuvant Breast Cancer: A Randomized Controlled Trial, Nutrition and Cancer (2025)
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Medically reviewed by Prof. Giorgi Pkhakadze, MD, MPH, PhD. Spotted an error? Contact the editorial team.
