Prostate cancer risk and serum levels of insulin and leptin: a population-based study

Background: In a previous study of Chinese men, we found that men with a higher waist-to-hip ratio (WHR) have a higher prostate cancer risk. Because leptin and insulin are related to body fat distribution, we examined whether leptin and insulin were associated with prostate cancer risk. Methods: Blood samples were collected from 128 case patients with incident prostate cancer and from 306 healthy control subjects randomly selected from residents of Shanghai, China. Epidemiologic information and anthropometric measurements were collected in personal interviews. Serum leptin, insulin, and sex hormone levels were measured by radioimmunoassay, and insulin-like growth factor-I (IGF-I) was measured by enzyme-linked immunosorbent assay. Multiple logistic regression analyses were used to estimate odds ratios for prostate cancer in relation to serum insulin and leptin levels. All statistical tests were two-sided, Results: After adjustment for body mass index, WHR, IGF-I, and sex hormone levels, higher serum insulin levels were associated with a statistically significantly elevated risk of prostate cancer (P < .001). Men in the highest tertile of insulin levels had a 2.56-fold (95% confidence interval [CI] = 1.38 to 4.75) risk of prostate cancer compared with men in the lowest tertile. Regardless of the tertile level of WHR, higher serum insulin levels were associated with an increased risk of prostate cancer: Men in the highest tertiles of WHR (>0.900) and insulin (>8.83 rhoU/mL) had 8.55 times (95% CI = 2.80 to 26.10) the prostate cancer risk of men in the lowest tertiles of both, and those in the lowest tertile of WHR (<0.873) and highest tertile of insulin had 4.30 times (95% CI = 1.17 to 15.70) the risk. By contrast, the association between leptin levels and prostate cancer risk was not statistically significant. Conclusion: Our results suggest that serum insulin levels may influence the risk of prostate cancer in Chinese men. Further research, especially prospective studies, is needed to confirm these findings in high-risk populations and to clarify the underlying mechanisms involved.