Serum 25-hydroxyvitamin D concentrations and colorectal cancer incidence in adults with type 2 diabetes.

Background: To examine the association of serum 25-hydroxyvitamin D (25[OH]D) with colorectal cancer (CRC) risk in adults with type 2 diabetes (T2D).

Methods: Using UK Biobank data, this study included 18,453 adults with T2D. Serum 25(OH)D concentrations were determined by the chemiluminescent immunoassay method. A Cox proportional hazards model was used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for CRC outcomes.

Results: During a median follow-up of 8.8 years, there were 284 incident CRC cases. Compared with adults with serum 25(OH)D concentrations <25.0 nmol/L, the adjusted HRs (95% CIs) for lower to higher serum 25(OH)D concentrations (25.0 to <50.0, 50.0 to <75.0, and ≥75.0 nmol/L) were 0.61 (0.46-0.82), 0.50 (0.34-0.74), and 0.53 (0.30-0.94), respectively (P = 0.001). The risk of CRC decreased by 19.0% for per 1-SD increment in serum 25(OH)D concentrations. A nonlinear association of serum 25(OH)D concentrations with CRC risk was observed using a restricted cubic spline analysis (P nonlinearity = 0.002).

Conclusions: Higher serum 25(OH)D concentrations were significantly and nonlinearly associated with a lower risk of CRC. These findings highlight the potential benefits of maintaining adequate vitamin D levels in CRC prevention among adults with T2D.