As already indicated previously, testosterone levels, particularly bioavailable testosterone, fall with advancing age. This decline in testosterone availability may start to occur early in the forth decade but it usually becomes clinically manifest in the 50s and 60s. Although there is continuing debate about the best way to diagnose hypogonadism in the aging male, there appears to be a general consensus that symptomatic men with reduced levels of testosterone should be given a trial of testosterone therapy if there is no contraindication to do so (Bain et al 2007).
The most common "out of balance" testosterone levels are found to be on the low side of normal; this occurs because a male's highest testosterone level usually peaks at about age 20, and then it decreases slowly with age. It has been suggested that a 1% decrease in testosterone level per year is not unusual for middle-aged (30 to 50 years old) and older males. While this decrease may not be noticeable in some men, others may experience significant changes starting in their middle-aged years or more commonly at age 60 and above. This drop in testosterone levels is sometimes termed hypogonadism, "male menopause" or andropause.
I am also suspect of the fact that men 100 years ago had testosterone levels of 800-2000 ng/dL. The truth is that there are men today that are stronger and more muscular than the men from 100 years ago. Sure the “average man” of today is less than the “average man” of prior generations, but this is because we sit around in offices all day, and then come home to sit on the couch and watch tv…little to no activity.
Remember that each person is unique, and each body responds differently to treatment. TT may help erectile function, low sex drive, bone marrow density, anemia, lean body mass, and/or symptoms of depression. However, there is no strong evidence that TT will help memory recall, measures of diabetes, energy, tiredness, lipid profiles, or quality of life.
However, testosterone is only one of many factors that aid in adequate erections. Research is inconclusive regarding the role of testosterone replacement in the treatment of erectile dysfunction. In a review of studies that looked at the benefit of testosterone in men with erection difficulties, showed no improvement with testosterone treatment. Many times, other health problems play a role in erectile difficulties. These can include:
Like other steroid hormones, testosterone is derived from cholesterol (see figure). The first step in the biosynthesis involves the oxidative cleavage of the side-chain of cholesterol by cholesterol side-chain cleavage enzyme (P450scc, CYP11A1), a mitochondrial cytochrome P450 oxidase with the loss of six carbon atoms to give pregnenolone. In the next step, two additional carbon atoms are removed by the CYP17A1 (17α-hydroxylase/17,20-lyase) enzyme in the endoplasmic reticulum to yield a variety of C19 steroids. In addition, the 3β-hydroxyl group is oxidized by 3β-hydroxysteroid dehydrogenase to produce androstenedione. In the final and rate limiting step, the C17 keto group androstenedione is reduced by 17β-hydroxysteroid dehydrogenase to yield testosterone.
Does the diminution that age brings with it in both total and bioavailable T have any clinical significance? This question leads us to the theme of this paper, “The Many Faces of Testosterone”. If testosterone were simply a “sex hormone” involved only with sexual desire and arousal we might tend to dismiss testosterone treatment in the aging man as merely a “life-style” therapy without any substantive basis for broad physiological necessity. The fact is, however, that the sexual attributes of testosterone are the least of its physiological necessities and that testosterone has a broad spectrum of demonstrated physiological functions as well as a wide variety of physiological and pathophysiological associations about which we are just learning.
Although some men believe that taking testosterone medications may help them feel younger and more vigorous as they age, few rigorous studies have examined testosterone therapy in men who have healthy testosterone levels. And some small studies have revealed mixed results. For example, in one study healthy men who took testosterone medications increased muscle mass but didn't gain strength.