Vitamin D supplementation boosts chemotherapy effectiveness by 79% in breast cancer

Breast cancer continues to affect a growing number of women, and many experience recurrence after treatment. However, it appears that supplementing with 50 micrograms of vitamin D daily may boost the effectiveness of chemotherapy by as much as 79%, representing major potential for improving treatment outcomes. This is according to a Brazilian population study published in Nutrition and Cancer. According to the researchers, vitamin D plays a significant role in both the development and treatment of breast cancer. This is partly because vitamin D is important for immune function, the elimination of abnormal cells, and the regulation of chronic inflammation.

The new Brazilian population study was conducted at São Paulo State University and aimed to investigate the effect of vitamin D supplementation in women with breast cancer receiving neoadjuvant chemotherapy (NCT). This type of chemotherapy is administered before primary surgery in order to shrink the tumor and make it easier to remove surgically.
More specifically, the vitamin D treatment was designed to evaluate vitamin D’s effect on the chemotherapy’s pathological complete response (pCR), meaning that there were no longer any signs of active cancer after surgical removal of the breast tissue and lymph nodes.
The study included 80 women with breast cancer aged 45 years and older who were scheduled to receive neoadjuvant chemotherapy followed by surgery.
The women were divided into two groups. One group received a daily supplement of 50 micrograms of vitamin D (= 2,000 IU), while the other group received a placebo. The study lasted six months.

Significantly better treatment outcomes, including tumors disappearing completely

Vitamin D treatment proved to be highly relevant. Before the study began, vitamin D deficiency was found to be widespread in both groups, with levels below 50 nmol/L, which is considered the lower threshold value.
After six months, the study revealed the following:

• Most participants in the vitamin D group achieved blood vitamin D levels above 75 nmol/L, which are considered optimal levels
• The placebo group still had excessively low vitamin D levels in the blood (below 50 nmol/L)
• The group receiving vitamin D supplementation had a 79% higher pCR rate, indicating that the neoadjuvant chemotherapy worked far more effectively
• In the vitamin D group, 43% experienced complete disappearance of the tumor after treatment. This was seen in only 24% of the placebo group.

The researchers therefore conclude that women with breast cancer who receive 50 micrograms of vitamin D per day in addition to neoadjuvant chemotherapy tend to have a much better pathological response. This may make it considerably easier to surgically remove the entire tumor.

The overlooked importance of vitamin D for the immune system and overall health

It is widely known that vitamin D is important for calcium absorption and bone health. However, there is also growing evidence that vitamin D plays an important role in the immune system, which must fight microorganisms and abnormal cells, including cancer cells. In addition, vitamin D helps regulate chronic inflammation, which is associated with many types of cancer and chronic diseases.

Sources of vitamin D, requirements, and therapeutic use in cancer

In the Nordic countries, strong summer sunlight is the primary source of vitamin D, as the skin produces a precursor to the vitamin when exposed to sunlight. However, even though sunlight is far more abundant in southern regions such as Brazil, vitamin D deficiency remains a global health problem because many people avoid the sun, and the diet provides only modest amounts.
Official daily recommendations are 5-15 micrograms (= 200-600 IU) for most adults and 20 micrograms (800 IU) for the elderly and other vulnerable groups.
As demonstrated in the Brazilian study, most participants had low vitamin D blood levels, as they were below 50 nmol/L.
At the same time, the Brazilian Society of Rheumatology recommends considerably higher blood levels (between 100-175 nmol/L). Although these recommendations exceed the official upper reference limit of 160 nmol/L, there is growing evidence that patients with rheumatic diseases, multiple sclerosis, and cancer may have increased requirements.
Some cancer studies have therefore used larger weekly doses of 1,250 micrograms to rapidly optimize blood levels and saturate the cells. This corresponds to nearly 180 micrograms per day.
Despite this, the new Brazilian study revealed that a relatively modest daily supplement of 50 micrograms of vitamin D had a significant therapeutic effect on chemotherapy and breast cancer treatment. Moreover, this is a simple and inexpensive treatment without side effects.
There is also strong indication that for many people it may be relevant to continue vitamin D supplementation in order to maintain optimal blood levels throughout life.
According to the EU Scientific Committee on Food, the upper safe intake level for vitamin D is 100 micrograms per day for adults and children over the age of 11. This vitamin D dose is no higher than what most fair-skinned individuals can naturally produce on a sunny summer day while lightly clothed.

References:

Fundacâo de Amparo à Pesquisa do Estado de Sâo Paulo. Vitamin D boosts breast cancer treatment success by 79%. ScienceDaily April 28, 2026

Michelle Sako Omodei et al. Vitamin D Supplementation Improves Pathological Complete Response in Breast cancer Patients Undergoing Neoadjuvant Chemotherapy: A Randomized Clinical Trial. Nutrition and Cancer, 2025