What're the mechanisms of andropause?
Numerous researches have been conducted to explore the mechanism that triggers the decreased testosterone production with age. Theories that have been proposed include:
Loss of Hypothalamic Sensitivity. The major factor in aging is the dysfunction of the male reproductive homeostat
(hypothalamic - pituitary - testes axis), which leads to the progressive loss of hypothalamic sensitivity to the inhibitory effects of testosterone. This loss of hypothalamic sensitivity to the negative feedback loop of testosterone has been confirmed by a number of indirect studies.
Testicular Defect. Some researchers postulated that during aging, there is a concurrent decreased Leydig cell's response to LH. It is likely that this loss of Leydig cell activity is due to a desensitization of sex hormone receptors due to prolonged hyperstimulation by chronically elevated levels of LH (primarily) and FSH (both of which are the result of the loss of hypothalamic sensitivity).
SHBG Level Increase. Levels of total plasma testosterone are known to have a progressive age-related decrease after the age of 50. One explanation is that both SHBG levels increase with age and albumin level decrease with age. This results in a decline in bioavailable testosterone. It has been noted that the decline in bioavailable testosterone is greater than the decline in total circulating testosterone. The circulating testosterone, which is bound to SHBG, is biologically less active than the free form.
Circadian Rhythm Dysfunction. Many people past the age of 40 have increased difficulty sleeping. A variety of factors such as stress, diet and a disturbance of the sleep wake cycle can influence sleep quality. All these factors pose as adverse effects on other biological rhythms, resulting in a dramatic shift of the circadian rhythm of testosterone production. Testosterone levels in young men are highest in the evening and early morning. However, this rhythm is greatly attenuated in older men. Therefore, maintaining a good nights sleep as well as a regular sleep-wake cycle is a sensible approach to reducing stress and normalizing our chrono-biological clock.