OBJECTIVE: The aim of this study is to determine the importance of serum Vitamin D (VD) levels in cancer pathogenesis and to investigate its relationship with cancer subtypes.
PATIENTS AND METHODS: This study included 4914 individuals, 1027 cancer patients and 3887 healthy subjects. The cancer patients were divided into five groups by cancer subtypes. The cancer patients and those in the control group were compared in terms of serum VD levels.
RESULTS: In the patients with cancer, the mean serum VD level was found to be significantly lower than that in the control group (16.1 ± 10.6 ng/mL vs. 19.6 ± 10.4 ng/mL, p = 0.000).  The VD levels were higher in breast cancer (BC) group than those in other cancer groups. The mean serum VD level was significantly lower in the BC group compared to the control group (18.1 ± 11.3 ng/mL vs. 19.6 ± 10.4 ng/mL, p = 0.004). In the ROC analysis, the cut-off VD value was determined as 15.2 ng/mL between those with and without cancer (area 0.634, OR: 95% CI 0.612-0.656, p = 0.000). VD <15.2 ng/mL was independently associated with cancer (OR, 2.096; 95% CI: 1.595 – 2.756, p = 0.000). Moreover, the decreased VD level was found to be independently associated with the increased cancer risk (OR, 1.048; 95% CI: 1.032- 1.065, p = 0.000).
CONCLUSIONS: Although there was no difference in VD levels among the cancer patients and there was less difference in the BC patients compared to the healthy individuals, the VD level was significantly lower in all cancer patients compared to healthy people. In addition, there was an independent positive association between VD levels and cancer, with the VD values below 15.2 ng/mL increasing the cancer risk.