Meta-analysis: longitudinal studies of serum vitamin D and colorectal cancer risk

P>Background In 1980, Garland hypothesized that lower levels of vitamin D resulting from much weaker UV-B radiation at higher latitudes may account for the striking geographical pattern of cancer mortality. Further research has been conducted over the past 20 years. Aim To perform a systematic review and meta-analysis of longitudinal studies on the association between serum 25 hydroxyvitamin D (25(OH)D) and the risk of colorectal cancer (CRC). Methods Relevant studies published until September 2008 were identified by systematically searching Ovid Medline, EMBASE, and ISI Web of Knowledge databases and by cross-referencing. Due to the heterogeneity of studies in categorizing serum vitamin D levels, all results were recalculated for an increase of serum 25(OH)D by 20 ng/mL. Summary odds ratios (ORs) were calculated using meta-analysis methods. Results Overall, eight original articles reporting on the association between serum 25(OH) D and CRC risk were included. In meta-analyses, summary ORs (95% confidence intervals) for the incidence of CRC, colon cancer and rectal cancer associated with an increase of 25(OH)D by 20 ng/mL were 0.57 (0.43-0.76), 0.78 (0.54-1.13) and 0.41 (0.11-1.49). No indication for publication bias was found. Conclusions Our results support suggestions that serum 25(OH)D is inversely related to CRC risk.