Introduction: Several nested case-control studies have found that high serum or plasma levels of 25-hydroxy vitamin D (25OHD) are associated with decreased risk of colorectal cancer. Most of these studies were conducted in areas with lower UVB irradiance than Australia. To determine whether 25OHD was associated with reduced risk of colorectal cancer in Australia, we conducted a case-cohort study nested within a cohort study.
Methods: The Melbourne Collaborative Cohort recruited 41,514 participants from 1990-94. At baseline, blood samples were collected. This study was restricted to participants with dried blood spots from baseline blood samples. We included a random sample of 2996 people (i.e. subcohort), together with all incident cases of colorectal cancer during follow-up. 25OHD was measured using liquid chromatography tandem mass-spectrometry. The data were analysed with Cox regression, using Barlow's method to allow for the case-cohort design and adjusted for sex, education, physical activity, waist circumference, country of birth (southern Europe versus other), smoking, and intakes of alcohol, energy, margarine and processed meat.
Results: The method showed high reliability; the intra-class correlation from 500 repeat measurements was 0.78 (95% CI: 0.75, 0.82). In a separate calibration study, there was good agreement between 25OHD measurements from dried blood spots and plasma and for the subcohort, the predicted mean plasma concentrations were 55.5 nmol/L for males and 46.0 for females. During an average of 14 years of follow-up, we identified 563 cases. There was a weak, non-statistically significant inverse association between 25OHD and colorectal cancer; the hazard ratio for the highest versus lowest quartile was 0.82 (95% CI: 0.61, 1.10, p trend = 0.20).
Conclusions: In this Australian study, the association between 25OHD and risk of colorectal cancer was weaker than has been observed in studies from Europe and North America.
Citation Format: Dallas R. English, Elizabeth J. Williamson, Alicia K. Heath, Peter R. Ebeling, Laura Baglietto, Allison M. Hodge, Graham G. Giles, David Kvaskoff, Darryl Eyles. Vitamin D and risk of colorectal cancer: The Melbourne Collaborative Cohort Study. [abstract]. In: Proceedings of the Twelfth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2013 Oct 27-30; National Harbor, MD. Philadelphia (PA): AACR; Can Prev Res 2013;6(11 Suppl): Abstract nr A54.
- ©2013 American Association for Cancer Research.