Factors that Affect Testosterone Levels
The vicious circle of low testosterone and obesity has been described as the hypogonadal/obesity cycle. In this cycle a low testosterone level results in increased abdominal fat, which in turn leads to increased aromatase activity. This enhances the conversion of testosterone to estrogens, which further reduces testosterone and increases the tendency toward abdominal fat.
Testosterone binds more tightly to SHBG than to albumin. Consequently, only albumin-bound testosterone and free testosterone constitute the bioavailable forms of testosterone, which are accessible to target tissues and carry out the actions of the essential hormone. Thus, the bioavailability of testosterone is influenced by the level of SHBG.
Aging men experience both an increase in aromatase activity and an elevation in SHBG production. The net result is an increase in the ratio of estrogen to testosterone and a decrease in total and free testosterone levels. It is crucial that this skewed ratio be balanced.