McCullough ML, et al. - Researchers investigated the protective function of vitamin D in colorectal carcinogenesis via analysis of experimental and epidemiological studies. Overall, they noted a link between elevated circulating 25(OH)D levels and statistically important, substantially lower colorectal cancer risk in women—as well as a non-statistically significant lower risk in men. They observed higher optimal 25(OH)D concentrations for colorectal cancer risk reduction (75-100 nmol/L) than the current Institute of Medicine (IOM) recommendations.

Methods

• The study sample consisted of 5,706 patients with colorectal cancer and 7,107 healthy control individuals with a wide range of circulating 25(OH)D concentrations.
• 25(OH)D levels were recalculated for 30.1% of participants.
• They calibrated previously measured 25(OH)D to the same assay to permit the estimating risk by absolute concentrations.
• They calculated study-specific relative risks (RRs) for prediagnostic season-standardized 25(OH)D levels via conditional logistic regression, and were pooled using random effects models.

Results

• They observed an association of deficient 25(OH)D (< 30 nmol/L) with 31% greater colorectal cancer risk; 25(OH)D above sufficiency (75 to < 87.5 and 87.5 to < 100 nmol/L) with 19% greater cancer risk; and 27% lower risk when compared with the lower range of sufficiency for bone health (50 to < 62.5 nmol/L), respectively.
• They did not identify a continuous decline in the risk at 25(OH)D of ≥ 100 nmol/L.
• When adjusting for body mass index, physical activity, or other risk factors, there was little impact on the associations.
• They reported 19% lower colorectal cancer risk in women and 7% lower in men for each 25 nmol/L increment in circulating 25(OH)D.
• Overall, inverse associations in all subgroups—including colorectal subsite, geographic area, and season of blood collection—were evident.