A study shows that in women diagnosed with breast cancer, adequate serum vitamin D levels are associated with a beneficial prognosis in the years following. Hence the importance of blood tests to determine which patients might benefit from supplementation.

Good, vitamin, D, levels, may, improve, breast, cancer, outcomes

Vitamin D is essential for the formation, growth and repair of bones, for the normal absorption of calcium and for the proper functioning of the immune system. This vitamin is mainly produced by the skin, under the action of the sun's ultraviolet rays, but it is also found in certain types of food. Numerous scientific studies have been carried out concerning a possible protective role of vitamin D against the risk of cancer. In particular, the relationship between vitamin D and the risk of breast cancer remains questionable, although a growing body of evidence suggests that this nutrient may reduce this risk.

In this area, a new study makes the case for maintaining adequate biological levels of vitamin D, especially in populations with low serum levels. Conducted by researchers at Roswell Park Comprehensive Cancer Center, the study states that breast cancer patients who have adequate levels of vitamin D at the time of diagnosis have better long-term outcomes. "Combined with previous research findings, these new results suggest a continued benefit for patients maintaining adequate vitamin D levels during and beyond breast cancer treatment. ", the researchers explain. 

A beneficial effect, even at an advanced stage of the disease

The study involved nearly 4,000 patients who had their vitamin D levels checked by blood test at the time of diagnosis and were followed for a median of nearly 10 years. Patients were divided into three levels: vitamin D deficiency (less than 20 nanograms per milliliter in blood tests), insufficient (20 to 29 ng/ml) or sufficient (30 ng/ml or more). The results showed first that vitamin D supplementation, body mass index (BMI), and race/ethnicity were the most influential factors on serum vitamin D levels, while genetic variants had only a limited impact. 

The researchers then assessed these levels in relation to overall survival, breast cancer-specific survival, recurrence-free survival, and invasive disease-free survival after a median follow-up of 9.6 years. The results showed that women with sufficient levels of vitamin D were 27% less likely to die from any cause during 10 years of follow-up, and 22% less likely to die from a specific breast cancer. The scientific team also found that the association between vitamin D levels and breast cancer outcomes was similar regardless of the estrogen receptor status of the cancerous tumor.

Finally, the association appeared somewhat stronger in low-weight patients and those diagnosed with more advanced breast cancer. In addition, it turns out that black women had the lowest vitamin D levels, which may help explain poorer outcomes after breast cancer diagnosis. "Our results support the use of daily vitamin D supplementation to maintain adequate levels of vitamin D after breast cancer diagnosis, particularly in black women and patients diagnosed with advanced disease," said lead author Christine Ambrosone.

However, the scientific team notes that since these results were presented at an annual medical meeting, the American Society of Clinical Oncology, they should be considered preliminary until they are published in a peer-reviewed journal. Note that in 2010, an Inserm study supported an association between high serum levels of vitamin D and decreased risk of breast cancer. The researchers estimated that the value considered adequate was 30 ng/mL, although clinical trials with different doses are needed to confirm the benefit of vitamin D on breast cancer.