Diabetes mellitus and risk of prostate cancer: a meta-analysis

Aims/hypothesis. The association of diabetes mellitus with prostate cancer has been controversial. This study examines the strength of this association by conducting a detailed meta-analysis of the studies published in peer-reviewed literature on the subject. Methods. A comprehensive search for articles published up to 2003 was performed, reviews of each study were conducted and data were abstracted. Prior to meta-analysis, the studies were evaluated for publication bias and heterogeneity. Pooled relative risk (RR) was calculated using the random- and the fixed-effects models. Subgroup and sensitivity analyses were also performed. Results. We included 14 studies, published between 1971 and 2002, in the meta-analysis (five case-control studies, nine cohort studies). We found no evidence of publication bias (p=0.89) or heterogeneity among the studies (p=0.38). The association of diabetes with prostate cancer was statistically significant, both on the basis of a random-effects model (RR=0.91, 95% CI: 0.86 to 0.96), and on the basis of a fixed-effects model (RR=0.91, 95% CI: 0.88 to 0.94). When the analysis was stratified into subgroups according to study design, the association was inverse in both cohort and case-control studies, but only in the former was it statistically significant. The sensitivity analysis strengthened our confidence in the validity of this association. Conclusions/interpretation. Our meta-analysis findings provide strong evidence that people with diabetes have a significant decrease in risk of developing prostate cancer. There is biological evidence to support this association.