Vitamin D Increases the Success Rate of Breast Cancer Treatment by 79 Percent

Researchers in Brazil have found that a simple vitamin D supplement could help make chemotherapy more effective in women with breast cancer. The study, conducted at the Botucatu Medical School of the State University of São Paulo (FMB-UNESP), suggests that low doses of the vitamin improve treatment outcomes and could potentially serve as a more accessible alternative to certain expensive or hard-to-obtain drugs designed to enhance the response to chemotherapy.

Breast cancer is the most common cancer among women worldwide. The risk increases significantly with age: while younger women are affected less frequently, breast cancer most commonly occurs from around age 50 onward. Other important risk factors include genetic predisposition (e.g., family history), hormonal influences, obesity, alcohol consumption, and lack of physical activity. At the same time, the earlier breast cancer is detected, the better the treatment outcomes generally are.

Higher Rates of Cancer Remission

The study funded by FAPESP included 80 women over the age of 45 who were preparing to begin treatment at the oncology outpatient clinic of the General and Teaching Hospital (“Hospital das Clínicas”) at FMB-UNESP. The participants were divided into two equal groups. One group received a daily dose of 2,000 IU (International Units) of vitamin D, while the other group received placebo tablets. All women underwent neoadjuvant chemotherapy, a treatment administered before surgery to shrink tumors and facilitate their removal.

After six months, the difference between the two groups was striking. Among those who took vitamin D, the cancer disappeared completely in 43% of cases following chemotherapy. In comparison, only 24% of participants in the placebo group achieved the same result.

“Even with a small number of participants, it was possible to observe a significant difference in response to chemotherapy. Furthermore, the dosage used in the study [2,000 IU per day] is far below the target dose for correcting a vitamin D deficiency, which is normally 50,000 IU per week,” says Eduardo Carvalho-Pessoa, president of the Brazilian Regional Society of Mastology in São Paulo and one of the authors of the study, which was published in the journal “Nutrition and Cancer.”

The Role of Vitamin D in the Immune System and Health

Vitamin D is best known for helping the body absorb calcium and phosphorus, which are crucial for maintaining strong bones. However, growing evidence suggests that it also plays a role in immune function and helps the body defend itself against infections and diseases, including cancer. Many previous studies examining vitamin D and cancer focused on much higher doses than those used in this study. The body produces vitamin D primarily through sun exposure, but it can also be obtained from certain foods. Current guidelines recommend 600 IU per day for most adults and 800 IU for older adults. The American Academy of Pediatrics recommends 400 IU daily for infants. Excessive intake can be harmful and lead to symptoms such as vomiting, weakness, bone pain, and kidney stones.

Low Vitamin D Levels and Response to Treatment

At the start of the study, most participants had low vitamin D levels, defined as less than 20 nanograms per milliliter (ng/ml) of blood. The Brazilian Society of Rheumatology recommends maintaining levels between 40 and 70 ng/ml. A key finding of the study was that a large proportion of the participants already had a significant vitamin D deficiency (below 20 ng/ml) before the start of chemotherapy. This is clinically relevant because vitamin D is not only important for bone metabolism but also plays a role in immune system function and cell regulation—processes that can be particularly relevant in breast cancer.

Daily administration of 2,000 IU of vitamin D caused blood levels to rise continuously during treatment. This increase could explain why patients in the supplement group responded better to therapy. One possible interpretation is that adequate vitamin D status increases the sensitivity of tumor cells to chemotherapeutic agents or simultaneously strengthens the immune system, allowing the body to respond more effectively to treatment.

Furthermore, this finding has an important public health and practical dimension: Compared to many modern cancer drugs, vitamin D is very inexpensive, readily available, and easy to administer. In healthcare systems with limited resources—such as Brazil’s public health system (SUS)—such measures could be particularly valuable, as some specialized drugs designed to improve treatment response are not widely available there.

“Supplementation caused levels to rise throughout the course of chemotherapy, which supports a potential contribution to patient recovery,” Carvalho-Pessoa told Agência FAPESP. “Vitamin D is an easily accessible and cost-effective option compared to other drugs used to improve response to chemotherapy, some of which are not even listed in the Unified Health System [the Brazilian national public health network, known as SUS, an acronym in Portuguese],” he added.

Promising Results, Further Research Needed

The results are particularly interesting because they point to a relatively simple, cost-effective supplement that could potentially have a measurable impact on treatment success in breast cancer. At the same time, however, it remains crucial to note that this is a comparatively small study with only 80 participants. In medical research, the rule is: the larger and more diverse the group studied, the more reliable and generally applicable the results are.

This is precisely where the researchers’ recommendations come in. Larger, randomized studies could verify whether the observed effect is indeed confirmed—across different age groups, tumor types, and treatment protocols. It is equally important to understand how vitamin D works biologically. Among other things, effects on the immune system, the tumor microenvironment, or the sensitivity of cancer cells to chemotherapy are being discussed.

If the results are confirmed, this would have several practical implications: Vitamin D levels could be routinely checked before the start of chemotherapy and specifically adjusted. This would be particularly relevant since, as shown in the study, many patients are already deficient. While this could not replace the therapy, it could potentially support it more effectively.