Abstract

<b> Introduction:</b> Breast cancer is the most frequent invasive malignancy in women worldwide. There is a modifiable risk factor (such as serum vitamin D level) for this cancer. We decided to conduct this study since the influence of serum vitamin D levels on breast cancer is still controversial. </br></br> <b> Methods and materials:</b> In this analytical cross-sectional study, 103 patients who were diagnosed with breast cancer were included. Patients' demographic, clinical and pathological features were all recorded. After the laboratory provided the serum vitamin D level, it was included in the checklist. Serum vitamin D level was categorized into 3 groups: <10 ng/ml, 1030 ng/ml and >30 ng/ml. The chi-square test was used to assess the relationship between vitamin D levels and clinicopathological features of the patients in SPSS software. The results were considered statistically significant at P-value < 0.05. </br></br> <b> Results:</b> The mean age of the patients was 47.97 8.8 years. The mean serum vitamin D level was 28.72 19.9 ng and it was divided into three groups: 1) deficient (10 ng), which included 20 (19.4) patients, 2) insufficient (10-30 ng), which included 48 (46.6) patients, and 3) normal (>30 ng), which included 35 (34) patients. Low vitamin D level (<320 ng/ml) was mainly detected in premenopausal cases (P-value = 0.001) with poor prognosis high grade of the disease (P-value = 0.001), positive nodal involvement (P-value = 0.025) and positive Ki-67 (P = 0.021). Furthermore, patients with lower serum vitamin D levels interact in fewer outdoor activities (P-value = 0.007), sleep less during the day (P-value = 0.001) and sleep later at night (P-value = 0.009). </br></br> <b>Conclusion:</b> Decreased serum 25(OH) D levels were linked with a higher histological grade of the tumor and lymph node involvement. Low serum 25(OH) D levels were also related to prognostic factors such as high Ki67 expression and the presence of negative hormone receptors (ER and PR). Our data support negative correlations between vitamin D levels and the risk of breast cancer with poor prognostic characteristics, based on observational research.