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Effects of age and sex hormones on transition and peripheral zone volumes of prostate and benign prostatic hyperplasia in twins.

Benign prostatic hyperplasia has been shown to increase with age and be influenced by sex hormones. The relationship between aging and hormonal influences on growth of zones of the prostate is unresolved. We studied the relationship of age and sex hormones on volume of prostate zones in 214 male twins between 25 and 75 yr old. Volumes of the total prostate (TV), transition zone (TZ), and peripheral zones (PZ) were measured using transrectal ultrasound, and sex steroid concentrations were measured using RIA. Using transformed data corrected for age, TV (r = 0.54, P < 0.00001), TZ (r = 0.58, P < 0.00001), and PZ (r = 0.39, P < 0.00001) volumes increased with age. However, the PZ volume rose more rapidly than the TZ before age 50, and TZ showed a steeper increase after age 50 yr than the PZ volume. The TZ, PZ, and ratio TZ/PZ correlated significantly (r = 0.87, 0.90, and 0.52, respectively; P < 0.00001). After a TV exceeded 30 g, the rise of the PZ became attenuated, and the slope of the TZ became steeper. Age-adjusted sex hormone concentration was not evaluated in men with larger prostate volumes. Men with American Urological Association symptom scores above 10 had significantly (P < 0.001) larger total prostate volume (TV) and TZ volume, but not PZ volumes, than men with scores below 10. Prostate volumes correlated inversely with age-adjusted serum testosterone (T), dihydrotestosterone, sex hormone binding globulin, and sex hormone binding globulin-bound T concentrations. These results demonstrate that before age 50 yr or before a prostate weight exceeds 30 g, prostate growth may be mainly from enlargement of the PZ and after age 50, the TZ. In addition, elevated T and dihydrotestosterone concentrations do not predispose men to prostate enlargement or symptoms of benign prostatic hyperplasia.