Higher Post-operative Serum Vitamin D Level Is Associated With Better Survival Outcome In Colorectal Cancer Patients

25-hydroxyvitamin D (25-OHD) may have a prognostic value in colorectal cancer (CRC) patients. However, as 25-OHD concentration is strongly impacted by surgery, it is uncertain what is the most reliable time-point for 25-OHD assessment, pre- or post-operative. Therefore, we examined 515 CRC patients (AJCC I-III) who underwent surgery. Blood samples were collected either pre-operatively (n=286; median=1 day before surgery) or post-operatively (n=229; median=8 days). Serum 25-OHD concentration was determined by liquid chromatography-tandem mass spectrometry. Association between 25-OHD and survival was tested in the whole cohort, followed by stratified analyses in pre-and post-operatively sampled. Median 25-OHD in the cohort was 36.7 nmol/L and median follow-up time was 5.9 years. There were no differences between pre-and post-operative cohort in age, sex, 25-OHD, AJCC stage or localization of tumour. After adjustment, higher 25-OHD (>50 nmol/L) was associated with better overall survival only in post-operative (HR=0.53; 95%CI: 0.33-0.84; P=0.006), but not in pre-operative cohort (HR=1.13; 95%CI: 0.77-1.65; P=0.53). In conclusion, higher post-operative 25-OHD levels were associated with better survival outcome in CRC patients, while no such association was found for pre-operative levels. Time-point of blood collection should be addressed carefully in future research as it might affect the prognostic value of 25-OHD in CRC