OBJECTIVETo investigate the changes of serum reproductive hormones with male aging and to compare the differences in the hormone levels among different age groups or between township and rural males of the same age group.

METHODSUsing cluster and stratified sampling, we recruited 434 healthy old and middle-aged (40-69 years) males, 198 from the township and 236 from the rural communities. We determined the concentrations of serum total testosterone (tT), luteinizing hormone (LH) and sex hormone binding globulin (SHBG), free testosterone (fT), bio-available testosterone (Bio-T), and obtained the testosterone secretion index (TSI) and free testosterone index (fTI). Meanwhile, we included fifty-nine 20-39 years old males from the same communities in a control group.

RESULTSWith the increase of age, the serum tT levels did not change significantly, while the levels of serum LH and SHBG increased, and those of fT, Bio-T, TSI and fTI decreased gradually. Statistically significant differences were found among the four different age groups in all the parameters of reproductive hormones (P < 0.01), except in the serum tT level (P > 0.05). The serum tT level was not significantly correlated with aging and LH (P > 0.05). Serum LH and SHBG had a marked positive correlation with aging, and SHBG with LH (P < 0.01), while fT, Bio-T, TSI and fTI were negatively correlated with aging and the LH level (P < 0.01). Serum LH, TSI and fTI showed statistical differences (P < 0.05), while fT and Bio-T exhibited extremely significant differences (P < 0.01) between the township and rural males in the 40 -49 yr group, and in the same age group, the increase rates of serum LH and SHBG and reduction rates of fT, Bio-T, TSI and fTI were higher in the rural men than in the township residents. However, the results were just the opposite in the 50 - 59 and 60 - 69 yr groups.

CONCLUSIONThe levels of serum LH, SHBG, fT, Bio-T, TSI and fTI changed with aging in a gradientmanner in the old and middle-aged males, but no significant changes were observed in the level of serum tT. There were statistical differences in many parameters of serum reproductive hormones among different age groups or between township and rural males.