History of diabetes mellitus and risk of prostate cancer in physicians

Some studies have suggested that diabetes mellitus may decrease the risk of prostate cancer because of lower insulin levels. To further investigate the relation between diabetes and prostate cancer, a nested case-control study was conducted within the US Physicians' Health Study. Cases (n = 1,110) had been diagnosed with prostate cancer, confirmed on medical record review, during follow-up in 1982-1995. Controls (n = 1,110) were selected randomly from men free of prostate cancer and were matched on age and date of randomization. Information on personal history of diabetes and other diseases, lifestyle habits, and body weight/height was self-reported. Logistic regression analysis showed that the odds ratio for prostate cancer was 0.64 (95% confidence interval (CI): 0.43, 0.95) for men with diabetes, relative to those without the disease, after adjustment for potential confounders. Odds ratio estimates were 0.63 (95% CI: 0.35, 1.14), 0.77 (95% CI: 0.35, 1.72), 0.59 (95% CI: 0.21, 1.66), and 0.59 (95% CI: 0.27, 1.27) for diabetes diagnosed 1-5, 6-10, 11-15, and > or = 16 years prior to prostate cancer diagnosis (p for trend < 0.05). Adjusted odds ratios were 1.44 (95% CI: 0.34, 6.17) for stage A prostate cancer and 0.48 (95% CI: 0.28, 0.83) for stages B-D. Results suggest that history of diabetes may be associated with a decreased risk of prostate cancer, especially late-stage tumors.