Do differences in age specific androgenic steroid hormone levels account for differing prostate cancer rates between Arabs and Caucasians?

Objective: Factors responsible for the low incidence of clinical prostate cancer in the Arab population remain unclear, but may be related to differences in androgenic steroid hormone metabolism between Arabs and other populations, especially as prostate cancer is believed to be androgen dependent. We therefore measured the levels of serum androgenic steroids and their binding proteins in Arab men and compared results obtained with values reported for Caucasian populations to determine if any differences could at least partially account for differences in incidence of prostate cancer rates between the two populations. Methods: Venous blood samples were obtained from 327 unselected apparently healthy indigenous Arab men (Kuwaitis and Omanis) aged 15–79 years. Samples were also obtained from 30 Arab men with newly diagnosed prostate cancer. Serum levels of total testosterone (TT), sex hormone binding globulin (SHBG), derived free androgen index (FAI); adrenal C19-steroids, dehydroepiandrosterone sulfate (DHEAS) and androstenedione (ADT) were determined by chemiluminescent immunoassay. Age specific reference intervals, mean and median for each analyte were determined. Frequency distribution pattern for each hormone was plotted. The reference range for hormones with normal distribution was mean ± 2SD and 2.5–97.5% for those with non-normal distribution. The mean serum levels of the hormones in Arab men with prostate cancer were compared with values in healthy age-matched Arab men. Results: There was a significant decrease between the 21–29 years age group and the 70–79 years age group for TT (-38.77%), DHEAS (-70%), ADT (-36%) and FAI (-63.25%), and an increase for SHBG (+64%). The calculated reference ranges are TT (2.73–30.45 nmol/L), SHBG (6.45–65.67 nmol/L), FAI (14.51–180.34), DHEAS (0.9–11.0 µmol/L) and ADT (0.54–4.26 ng/mL). The mean TT, SHBG, DHEAS and ADT in Arab men were significantly lower than those reported for Caucasians especially in the 21–29 years age group. Arab men with newly diagnosed prostate cancer had higher serum TT (P < 0.7), ADT (P < 0.2), SHBG (P < 0.2) and lower DHEAS (P < 0.008) compared to aged matched controls. Conclusions: Serum TT, SHBG, DHEAS and ADT levels are significantly lower in Arab men compared to those reported for Caucasian men, especially in early adulthood. Arab men with newly diagnosed prostate cancer have higher circulating androgens compared to healthy controls. We suggest that low circulating androgens and their adrenal precursors in Arab men when compared to Caucasians may partially account for the relatively lower risk for prostate cancer among Arab men.