This is because in men, testosterone is linked to a great deal of functions that not only determine your quality of life, but quality of health. As men age, testosterone decreases. This can begin as early as 30. Most laboratory tests give an acceptable range for testosterone between 250 and 1000. This is a wide scope but symptoms can arise at levels of 300-500 as well. The rate of testosterone decline and symptom occurrences varies by individual. The following chart summarizes an approximate trend of testosterone decline.
Testosterone is made mainly in the testes and is under tight regulatory control of the brain and its hormones in the pituitary gland and the hypothalamus. The body controls testosterone production by using T levels as a stimulus to the brain to either make more (in times when levels decrease) or make less (when levels are normal). This delicate system involves 3 separate sets of hormones that act as a checks-and-balances system that keeps levels optimal. Even subtle imbalances in this system can lead to decreased T levels. Testosterone production will decrease through normal aging due to decreased testicular production despite a proper brain stimulus. This is one of the most common reasons for med to have symptoms and seek therapy. Other reasons for Low T include certain types of brain tumors, obesity, and unknown reasons why the brain simply does not respond to low levels and does not stimulate production.