Aim: We aimed to assess the association between deficient levels of circulating vitamin D, dietary intake of vitamin D, calcium and retinol, and risk of colorectal cancer in an Iranian population.
Methods: In this retrospective case-control study that was conducted between 2012 and 2015, 278 first incident colorectal cancer cases (colon cancer = 103; rectal cancer = 175), and 278 sex and age matched healthy controls (HCs) were recruited. Serum 25(OH)D, dietary vitamin D, and calcium intake were assessed. Logistic regression was used to estimate the odds ratio (OR) between studied factors and colorectal cancer. Estimates of OR were calculated according to both bivariate analyses based on the matching factors and multivariate analyses, with additional adjustment for potential confounders.
Results: A strong inverse linear dose-response association was seen between serum 25(OH)D and colorectal cancer (P for trend = .002). In comparison to serum 25(OH)D more than 40 nmol/L, lower serum concentrations were significantly associated with an increased OR of colorectal cancer. When analyzing anatomical subsites separately, lower circulating 25(OH)D was associated with higher OR for both colon and rectum cancers. Dietary vitamin D and calcium intake were not associated with colorectal cancer. Interaction analysis between serum 25(OH)D and the amount of calcium intake demonstrated that the lowest level of both factors was associated with an increased OR of colorectal cancer. The highest OR of colorectal cancer that was associated with lowest circulating 25(OH)D was stronger at the highest retinol intakes.
Conclusion: This study demonstrated an inverse strong association between 25(OH)D concentration and colorectal cancer in an Iranian population.
Keywords: calcium; colon cancer; colorectal cancer; rectum cancer; vitamin D.
© 2021 John Wiley & Sons Australia, Ltd.