The changes in average serum testosterone levels with aging mean that the proportion of men fulfilling a biochemically defined diagnosis of hypogonadism increases with aging. Twenty percent of men aged over 60 have total testosterone levels below the normal range and the figure rises to 50% in those aged over 80. The figures concerning free testosterone are even higher as would be expected in view of the concurrent decrease in SHBG levels (Harman et al 2001).
Individuals with metabolic syndrome are at increased risk for developing coronary artery disease and diabetes mellitus. Predicting who might develop the metabolic syndrome would allow preventive measures to be taken in addition to weight control and other lifestyle modifications such as cessation of smoking and increased exercise. It is known that with decreasing testosterone availability in aging males there is an increase in fat mass and decrease in lean body mass (van den Beld et al 2000), there are disorders of insulin and glucose metabolism (Haffner et al 1996) and dyslipidemia (Tsai et al 2004). Kupelian and colleagues (2006) in analyzing data from the Massachusetts Male Aging Study demonstrated that men with low levels of testosterone, sex hormone-binding globulin, or clinical androgen deficiency, especially men with a BMI of greater than 25, were at increased risk of developing the metabolic syndrome and hence, diabetes mellitus and/or coronary artery disease.
Changes in body composition are seen with aging. In general terms, aging males are prone to loss of muscle mass and a gain in fat mass, especially in the form of visceral or central fat. An epidemiological study of community dwelling men aged between 24 and 85 years has confirmed that total and free testosterone levels are inversely correlated with waist circumference and that testosterone levels are specifically related to this measure of central obesity rather than general obesity (Svartberg, von Muhlen, Sundsfjord et al 2004). Prospective studies show that testosterone levels predict future development of central obesity (Khaw and Barrett-Connor 1992; Tsai et al 2000). Reductions in free testosterone also correlate with age related declines in fat free mass (muscle mass) and muscle strength (Baumgartner et al 1999; Roy et al 2002). Studies in hypogonadal men confirm an increase in fat mass and decrease in fat free mass versus comparable eugonadal men (Katznelson et al 1998). Taken together, the epidemiological data suggest that a hypogonadal state promotes loss of muscle mass and a gain in fat mass, particularly visceral fat and therefore mimics the changes of ‘normal’ aging.
In summary it’s important to know that this topic is still hotly debated, and there are a lot of inconsistencies in the data. We do know that soy contains phytoestrogens and does seem to have a lot of affects on the body, including some studies that show decreased Testosterone levels. For that reason (and the fact that it tastes like ass) I avoid it, and I recommend you also avoid it (in particular soy isolates!) if you’re seeking higher testosterone.
Testosterone levels generally peak during adolescence and early adulthood. As you get older, your testosterone level gradually declines — typically about 1 percent a year after age 30 or 40. It is important to determine in older men if a low testosterone level is simply due to the decline of normal aging or if it is due to a disease (hypogonadism).