Breast cancer is the most common cancer among the female population worldwide. The incidence of breast cancer is increasing every year. This requires the search for new trigger factors that can contribute to the onset and course of this disease. One of these factors is vitamin D, which is constantly deficient in most of the world’s population. This article provides a review of clinical studies over the last 15 years on the relationship between serum vitamin D concentration and breast cancer risk, prognostic factors, survival and treatment outcomes, and the effect of vitamin D receptor status on breast cancer. Studies have shown heterogeneity in research results that found the relationship between low vitamin D levels and breast cancer risk, prognostic factors and survival. There was no heterogeneity in studies showing an association between decreased vitamin D receptor status and worse prognosis. The situation was similar when studying the effect of vitamin D on impro­ving treatment outcomes. Despite conflicting research results, most studies show a correlation between vitamin D deficiency and breast cancer risk, prognostic factors, survival and treatment outcomes. Therefore, the selected vector of scientific researches is rational both from the point of view of eliminating the pandemic of vitamin D deficiency among the world’s population and preventing the spread of breast cancer.