Higher serum vitamin D concentrations are longitudinally associated with better global quality of life and less fatigue in colorectal cancer survivors up to 2 years after treatment.

Background:Vitamin D status may be an important determinant of health-related quality of life of colorectal cancer (CRC) survivors. The current study investigated longitudinal associations between serum 25-hydroxyvitamin D3 (25OHD3) concentrations and quality of life in stage I-III CRC survivors up to 2 years post-treatment. Methods:CRC patients (n=261) were included upon diagnosis. Home visits (including blood sampling) were performed at diagnosis and at 6 weeks, 6 months, 1 and 2 years post-treatment. Serum 25OHD3 concentrations were measured using liquid chromatography-tandem mass spectrometry and adjusted for season. Validated questionnaires were used to assess global quality of life and cognitive functioning (EORTC-QLQ-C30), fatigue (EORTC-QLQ-C30 and Checklist Individual Strength, CIS), and depression and anxiety (Hospital Anxiety and Depression Scale). Statistical analyses were performed using linear mixed-models and adjusted for sex, age, time since diagnosis, therapy, comorbidities, physical activity, and BMI. Results:At diagnosis, 45% of patients were vitamin D deficient (<50 nmol/L). After treatment, 25OHD3 concentrations increased on average with 3.1 nmol/L every 6 months. In confounder-adjusted models, 20 nmol/L increments in 25OHD3 were longitudinally associated with increased global quality of life (β 2.9; 95%CI 1.5,4.3) and reduced fatigue (EORTC-QLQ-C30 subscale: β -3.5; 95%CI -5.3,-1.8 and CIS: β -2.8; 95%CI -4.7,-0.9). Observed associations were present both within and between individuals over time. Conclusions:Higher concentrations of 25OHD3 were longitudinally associated with better global quality of life and less fatigue in CRC survivors. Impact:This study suggests that higher 25OHD3 concentrations may be beneficial for CRC survivors. Intervention studies are needed to corroborate these findings.