Researchers studied 223 breast cancer patients to see if vitamin D levels could predict how well they’d respond to chemotherapy before surgery. They found that patients with higher vitamin D levels (at least 14.5 ng/mL) were more likely to have a complete response to treatment, meaning the cancer shrank significantly or disappeared. The study also looked at blood markers related to inflammation and found that certain inflammatory markers were linked to better or worse treatment outcomes. These findings suggest that checking vitamin D levels before starting chemotherapy might help doctors predict which patients will benefit most from their treatment.

The Quick Take

  • What they studied: Whether vitamin D levels and blood inflammation markers can predict how well breast cancer patients will respond to chemotherapy given before surgery
  • Who participated: 223 breast cancer patients who received chemotherapy before surgery between December 2022 and December 2024
  • Key finding: Patients with vitamin D levels of 14.5 ng/mL or higher were significantly more likely to have a strong response to chemotherapy, with about 39% of all patients showing complete response to treatment
  • What it means for you: If you’re facing breast cancer treatment, your doctor might want to check your vitamin D level before starting chemotherapy. Having adequate vitamin D may improve your chances of a good response, though this is one study and more research is needed. Talk to your doctor about whether vitamin D testing or supplementation makes sense for your situation.

The Research Details

This was a retrospective study, meaning researchers looked back at medical records of patients who had already received treatment. They collected information about vitamin D levels and various blood markers (measurements that show inflammation) from 223 breast cancer patients before they started chemotherapy. The researchers then compared these measurements to how well each patient’s cancer responded to treatment. They used statistical methods to find the best vitamin D level that separated patients who responded well from those who didn’t, and they analyzed whether vitamin D and inflammation markers independently predicted treatment success.

The study examined different types of breast cancer based on hormone receptor status (HR+/HER2-, HER2+, and triple-negative breast cancer) to see if vitamin D’s effect differed by cancer type. Researchers also noted which patients had taken vitamin D supplements before starting treatment and compared their outcomes to those who hadn’t.

Understanding what predicts chemotherapy success is important because it helps doctors know which patients might benefit most from this treatment and which ones might need different approaches. Vitamin D is interesting because it’s relatively easy and inexpensive to measure, and it’s something patients can potentially improve through supplementation. If vitamin D truly helps predict outcomes, it could become a useful tool in treatment planning.

This study has some strengths: it included a reasonable number of patients (223) and looked at multiple inflammation markers, not just one. However, it’s a retrospective study, which means researchers couldn’t control all the factors that might affect outcomes—patients may have had different diets, sun exposure, or other health factors not captured in the records. The study was conducted over a relatively short time period (2022-2024), so results are recent. The findings need to be confirmed by other research teams before they can be widely applied in clinical practice.

What the Results Show

Among the 223 patients studied, 39% experienced a complete response to chemotherapy (meaning the cancer either disappeared or shrank dramatically). The researchers found that vitamin D levels of 14.5 ng/mL or higher were strongly associated with better treatment response. This threshold was identified through statistical analysis and was significant across different breast cancer types, though the effect was particularly strong in hormone receptor-positive and HER2-positive cancers.

Patients who had taken vitamin D supplements before starting chemotherapy showed better outcomes than those who hadn’t, suggesting that vitamin D status before treatment begins matters. The relationship between vitamin D and treatment response remained significant even after accounting for other factors like age and cancer type, indicating that vitamin D appears to have an independent effect on chemotherapy success.

The study also examined inflammation markers in the blood. Higher levels of certain inflammation markers (specifically CAR and AIP) were associated with worse treatment responses. This suggests that inflammation in the body may work against chemotherapy effectiveness, while adequate vitamin D may help by reducing inflammation or supporting immune function.

The study found that the effect of vitamin D on treatment response varied somewhat by breast cancer subtype. In hormone receptor-positive and HER2-positive cancers, the vitamin D effect was particularly clear. Even in triple-negative breast cancer (the most aggressive type), vitamin D levels still appeared to influence outcomes, though the relationship was somewhat less pronounced. This suggests that vitamin D may work through multiple mechanisms in different cancer types.

Previous research has suggested that vitamin D plays a role in cancer biology and immune function, but this is one of the first studies to specifically examine whether vitamin D levels before chemotherapy can predict treatment success in breast cancer. The findings align with earlier research showing that vitamin D supports immune function and may help regulate inflammation. However, most previous studies were smaller or focused on vitamin D’s general role in cancer prevention rather than treatment response prediction.

This study looked backward at existing medical records rather than following patients forward in time, which limits what we can conclude about cause and effect. The researchers couldn’t control for all factors that might affect vitamin D levels or treatment response, such as diet, sun exposure, or other supplements patients were taking. The study was conducted at specific hospitals over a short time period, so results might not apply equally to all populations. Additionally, the study didn’t randomly assign patients to different vitamin D levels—it simply observed what happened with the vitamin D levels patients naturally had. More research, ideally with larger groups of patients followed over longer periods, would strengthen these findings.

The Bottom Line

If you have breast cancer and are about to start chemotherapy, ask your doctor to check your vitamin D level. If it’s below 14.5 ng/mL, discuss with your doctor whether vitamin D supplementation before treatment might be appropriate. This is a moderate-confidence recommendation based on one study—it’s promising but not yet definitive. Your doctor should consider your individual situation, other health factors, and any medications you’re taking. Don’t use vitamin D supplementation as a replacement for standard cancer treatment.

This research is most relevant to people with breast cancer who are about to receive chemotherapy before surgery. It may be particularly relevant if you have hormone receptor-positive or HER2-positive breast cancer. If you’ve already completed chemotherapy, checking vitamin D now won’t change your past treatment, but it might be relevant for future health. People without cancer should not use this study as a reason to take high-dose vitamin D supplements, as the research is specific to cancer treatment contexts.

Vitamin D supplementation would need to begin before chemotherapy starts to potentially have an effect. The study looked at vitamin D status at baseline (before treatment), so any supplementation should ideally happen in the weeks before chemotherapy begins. Treatment response is typically assessed after chemotherapy is completed, which is usually several months after starting treatment. Don’t expect to feel immediate effects from vitamin D supplementation—the benefit appears to be in how your cancer responds to chemotherapy, not in how you feel day-to-day.

Want to Apply This Research?

  • If your doctor recommends vitamin D supplementation before cancer treatment, track your daily supplement intake (dose and date) and note your vitamin D blood test results before and after supplementation. Record the date you start chemotherapy and any follow-up test results showing treatment response.
  • Work with your doctor to establish a vitamin D supplementation routine if recommended. This might involve taking a daily vitamin D supplement (typically 1,000-4,000 IU daily, though your doctor may recommend different amounts). Set a daily reminder to take your supplement at the same time each day, and schedule a follow-up blood test 4-8 weeks before your chemotherapy is scheduled to begin.
  • Track vitamin D levels through regular blood tests as recommended by your oncology team. Document your baseline vitamin D level, any supplementation you take, and your chemotherapy response outcomes. If you’re supplementing with vitamin D, have your level rechecked periodically to ensure it’s in the target range. Share this information with your cancer care team so they can monitor whether vitamin D status correlates with your individual treatment response.

This research suggests a potential relationship between vitamin D levels and breast cancer chemotherapy response, but it is not yet definitive medical guidance. This study should not be used to make independent decisions about vitamin D supplementation or cancer treatment. Always consult with your oncologist or cancer care team before starting any supplements or making changes to your cancer treatment plan. Vitamin D supplementation is not a substitute for standard cancer treatment. If you have breast cancer or are at risk for breast cancer, work with qualified medical professionals who can evaluate your individual situation, medical history, and specific cancer type. This information is for educational purposes and should not replace professional medical advice.