Chemotherapy and vitamin D supplement use are determinants of serum 25-hydroxyvitamin D levels during the first six months after colorectal cancer diagnosis

Vitamin D metabolites, including 25-hydroxyvitamin D-3 (25(OH)D-3), may inhibit colorectal cancer (CRC) progression. Here we investigated cross-sectional and longitudinal associations of demographic, lifestyle and clinical characteristics with 25(OH)D-3 serum concentrations in CRC patients at diagnosis and six months later. In 1201 newly-diagnosed stage I-III CRC patients, 25(OH)D-3 levels were analysed twice. Multivariable linear regression was used to assess demographic, lifestyle and clinical determinants of 25(OH)D-3 levels at diagnosis and six months later. Linear mixed models were used to assess characteristics associated with changes in 25(OH)D-3 levels over time. Results of our study showed that vitamin D intake from diet or supplements, use of calcium supplements, BMI and disease stage were associated with 25(OH)D-3 levels at both time points. Six months after diagnosis, gender and having received chemo- and/or radiotherapy were also associated with 25(OH)D-3 levels. A stronger decrease in 25(OH)D-3 levels was observed in patients who underwent chemotherapy, compared to surgery only (beta-6.9 nmol/L 95 %CI -9.8; -4.0). Levels of 25(OH)D-3 levels increased in patients using vitamin D supplements compared to non-users (beta 4.0 nmol/L 95 %CI 1.2; 6.8). In conclusion, vitamin D supplement use and treatment appear to be important determinants of 25(OH)D3 levels during the first six months after CRC diagnosis, although the difference in 25(OH)D3 levels was minor.