Prostate specific antigen (PSA) concentrations are in part influenced by circulating androgens. Previous studies have shown that patients with type 2 diabetes are at increased risk of developing cancers such as pancreatic, liver and colon cancer. However, it has been suggested that the risk of developing prostate cancer is lower in these patients. The aim of the current study was to determine whether serum PSA concentrations in Japanese men with type 2 diabetes are lower than those in healthy age matched controls, and also to determine which factors may be associated with PSA concentrations in men with type 2 diabetes.

Serum PSA was measured in 224 men with type 2 diabetes and 1293 healthy men aged between 40 and 79 years. Men with known prostate abnormalities and PSA concentrations above 4 μg/L were excluded from the study. The relationship between PSA and other factors such as age, blood pressure, serum lipids, HbA1c, body mass index and diabetic complications were investigated. Further associations between serum PSA and bioavailable testosterone and dihydrotestosterone were also explored in a subgroup of randomly selected men with type 2 diabetes.

Serum PSA, measured by chemiluminescent immunometric assay, was found to be lower in men with type 2 diabetes compared with healthy men in all age groups except 40–49 years. As expected, a positive correlation was seen between serum PSA concentrations and age, while a negative correlation was found between PSA and serum triglyceride concentrations. Multiple regression analysis demonstrated that age and type 2 diabetes were independent determinants of serum PSA. No correlation was observed between HbA1c, blood pressure or bioavailable testosterone and dihydrotestosterone in men with type 2 diabetes.

In previous studies, the role of androgens in prostate tumourgenesis has been well established. Furthermore, men with type 2 diabetes have been shown to have lower serum testosterone concentrations than their healthy counterparts. The lower androgen concentrations seem to confer natural protection against prostate cancer.

In this study, men with type 2 diabetes were found to have lower PSA concentrations than healthy age matched controls. However, PSA was not correlated with bioavailable testosterone nor with diabetic complications. The main limitation of the study was that testosterone in healthy men was not measured and could not be compared with that amongst men with type 2 diabetes.