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 D3 (25(OH)D3), may inhibit colorectal cancer (CRC) progression. Here we investigated cross-sectional and longitudinal associations of demographic, lifestyle and clinical characteristics with 25(OH)D3 serum concentrations in CRC patients at diagnosis and six months later. In 1201 newly-diagnosed stage I-III CRC patients, 25(OH)D3 levels were analysed twice. Multivariable linear regression was used to assess demographic, lifestyle and clinical determinants of 25(OH)D3 levels at diagnosis and six months later. Linear mixed models were used to assess characteristics associated with changes in 25(OH)D3 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)D3 levels at both time points. Six months after diagnosis, gender and having received chemo- and/or radiotherapy were also associated with 25(OH)D3 levels. A stronger decrease in 25(OH)D3 levels was observed in patients who underwent chemotherapy, compared to surgery only (β-6.9 nmol/L 95 %CI -9.8; -4.0). Levels of 25(OH)D3 levels increased in patients using vitamin D supplements compared to non-users (β 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. ClinicalTrials.gov Identifier: NCT03191110