Hormonal profile of diabetic men and the potential link to prostate cancer

Objective Previous studies suggest men with diabetes may be at reduced risk for prostate cancer as compared to men without diabetes. To investigate potential biological mechanisms, hormonal profiles of diabetic men and non-diabetic controls were compared. Methods In the Health Professionals Follow-Up Study, plasma levels of C-peptide, testosterone, sex-hormone binding globulin, insulin-like growth factor-1, and insulin-like growth factor binding protein-3 were determined in 171 diabetic men and 3,001 non-diabetic controls. Multiple linear regression analysis was conducted and least square means were calculated for hormones of interest. Results Plasma levels of several hormones either <= 1, 1.1-6, 6.1-14.9, or >= 15 years after diagnosis with diabetes were examined. As time since diabetes diagnosis increased, plasma levels of C-peptide and IGFBP-3 significantly decreased (p for trend: C-peptide =.05, IGFBP-3 =.03). While testosterone and SHBG levels both significantly increased with increasing time since diabetes diagnosis (p for trend: testosterone =.02, SHBG =.002), the ratio of testosterone to SHBG decreased, suggesting a reduction in bioavailable testosterone. Plasma IGF-1 levels were lower in diabetics than non-diabetics, but no significant time trend was noted. Conclusion This study of hormonal profiles of diabetic versus non-diabetic men identified changes in diabetic men that may be consistent with reduced prostate cancer risk.