Research articleOptimal Vitamin D Status for Colorectal Cancer Prevention: A Quantitative Meta Analysis
Introduction
The Women’s Health Initiative1 demonstrated that a low dose of vitamin D did not protect against colorectal cancer within 7 years of follow-up; however, a meta-analysis indicates that a higher dose may reduce its incidence.
There were approximately 145,300 new cases and 56,300 deaths from colorectal cancer in the United States during 2005.2 An observation of higher age-adjusted mortality rates of colorectal cancer in the northern and northeastern United States compared to the southwest, Hawaii, and Florida led to a theory that vitamin D of mainly solar origin may reduce risk of colorectal cancer3 through a mechanism involving calcium metabolism, intercellular adherence, and contact inhibition. Since then, five observational studies have explored the association of serum levels of the main circulating form of vitamin D, 25-hydroxyvitamin D (25[OH]D) with risk of colorectal cancer.1, 4, 5, 6, 7 However, an overall dose–response gradient for the effect of serum levels of 25(OH)D on colorectal cancer risk has not been determined. This meta-analysis provides an estimated dose–response gradient that may be of help in planning for a useful role of vitamin D in control of colorectal cancer.
Section snippets
Study Inclusion
The PubMed database was searched for the period from January 1966 to December 2005 by using the terms (“vitamin D,” or “25-hydroxyvitamin D”), and (“cohort” or “case–control” or “case–cohort” or “incidence” or “occurrence” or “epidemiology”) and “human” as medical subject heading (MeSH) terms and words in the abstract. Articles were included if they were published in medical journals and included measures of association by quantile. A total of five studies were identified and all five met the
Results
Five studies of the association of serum 25(OH)D with risk of colorectal cancer were identified.1, 4, 5, 6, 7 All were nested case–control studies of prediagnostic serum collected from healthy volunteer donors who were then followed from 2–25 years for incidence (Table 1). Three studies reported statistically significant trends toward lower odds ratios in individuals with higher levels of 25(OH)D,1, 6, 7 while two reported trends in the same direction that were of borderline significance or not
Discussion
A meta-analysis increases power by combining the results of many studies. All known published studies of serum 25(OH)D and risk of colorectal cancer were included, and the results were homogenous. Pooling of such independent studies increases precision, because random fluctuation in any one study tends to be counterbalanced by results of other studies.
The data from two different studies of serum 25(OH)D in the Johns Hopkins cohort in Washington County MD had trends that were uneven but
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