Body mass index and the risk of prostate cancer

Daniel Lee McGee,1 Carlos J Crespo21Department of Mathematical Sciences, University of Puerto Rico, Mayaguez, Puerto Rico, 2School of Community Health, Portland State University, Portland, OR, USABackground: This article presents cohort studies that use data from the National Health Information Survey from 1986 to 1994 and compares the effectiveness of Cox proportional hazards models that assume a linear relationship between body mass index (BMI) and the risk of prostate cancer with models that assume a J-shaped relationship.Methods and results: Our study found that for black males over 40 years of age, neither a linear nor a J-shaped relationship yielded a statistically significant model. With white males over 40 years, assuming a linear relationship did not yield a statistically significant model (P = 0.582). When we assume a J-shaped relationship, the optimal change point where the risk of prostate cancer death is minimized occurs when the BMI is 25.5. Among white males over 40 years with BMI < 25.5, an inverse relationship was found (P = 0.009). Among white males over 40 years with BMI > 25.5, a direct relationship was found (P = 0.017).Conclusion: With this data set, we found that for white males over 40 years, Cox proportional hazards models that assume a J-shaped relationship between BMI and prostate cancer death provide a much better fit than models assuming a linear relationship.Keywords: body mass index, prostate cancer, J-shaped curve, Cox proportional hazards model, Kaplan-Meier model, National Health Information Survey