Age-related Changes in Luteinizing Hormone and Testosterone Levels in Korean Men

Changes in luteinizing hormone (LH), serum testosterone (T), and salivary T levels with age were examined in Korean men. Serum was obtained from 167 Korean men of different ages (20~69y), and the serum LH and T levels were measured. Saliva samples were also obtained, and the salivary T level was determined. The LH levels did not change considerably until 40 y of age (20s, 2.5±1.0; 30s, 2.7±1.5; and 40s, 2.5±1.8 mIU/mL) but increased significantly around 50 y (50s, 3.7±1.8 and 60s, 3.1±1.7 mIU/mL). Further, the serum T levels also did not change until 40 y of age (20s, 5.3±2.6, 30s, 4.4±1.4, 40s, 4.1±1.5 ng/mL) but decreased significantly at 50 y (50s, 3.4±1.5; 60s, 2.6±0.8 ng/mL). The salivary T levels also showed small changes until the age of 40 y (20s~40s, 0.11±0.015 ng/mL) but decreased significantly at 50 y (0.08±0.03 ng/mL). Thus, the relative ratio of salivary T to serum T levels did not change significantly in all the ages examined (2.4±0.9%). Linear regression analysis predicted that the LH levels increased 1.5%/y while the serum and salivary T levels decreased 1%/y and 0.8%/y, respectively. The serum T/LH ratio did not change considerably until the age of 40 y (20s~40s; 2.27±0.14) but decreased significantly (1.2±1.0) at 50 y. Age-related changes in the salivary T/LH ratio were very similar to those in the serum T/LH ratio. These results demonstrated that LH and T levels in serum or saliva did not change considerably until 40 y of age; instead, in Korean men, from 50 y of age, the LH level increased, while the T level decreased. This suggests that primary testicular failure that occurred due to aging (approximately 50 y) and caused this phenomenon. The present study also shows that the salivary T level can be an indicator of the free T level in serum although the salivary T level correlates weakly with the total T level in serum (r=0.53). Thus, information regarding salivary T levels may be useful for studying the age-related changes occurring in male testicular physiology.