Over the years, it is surprising that the need for studies to answer these issues has been, by and large, ignored by the specialties that were most highly impacted when the first reports of significant benefits began to appear in the 1940s, particularly in the cardiovascular arena. This does not mean that there have been no adequate studies investigating the physiologic effects of testosterone. Medline lists over 60,000 testosterone references since 1966.
Over the years, it is surprising that the need for studies to answer these issues has been, by and large, ignored by the specialties that were most highly impacted when the first reports of significant benefits began to appear in the 1940s, particularly in the cardiovascular arena. This does not mean that there have been no adequate studies investigating the physiologic effects of testosterone. Medline lists over 60,000 testosterone references since 1966. What has been clearly demonstrated by 65 years of availability is that treatment in physiologic doses to correct deficiency in young men has clear physiologic benefits and has rarely shown any serious side effects during replacement for long periods. With use in older men over 50, mostly derived from studies of the newer treatment methods, the potential side effects of testosterone are relatively mild, dose-related and reversible, at least over the short- or medium-term periods of one to five years. However, the risks or benefits of long-term use in aging men for five to 10 years or longer remain unknown.
Potential Adverse Effects
Common potential adverse effects, usually only seen with excessive doses, include:
- fluid retention; and
- worsening of sleep apnea.
Also included are other less serious effects such as:
- irritability or aggressive behavior;
- increasing benign prostate hyperplasia (BPH) symptoms;
- gynecomastia; or
- hair loss.
In the younger population these effects may be easily reversed with dosage changes and have little risk of serious sequelae. However, in the older age groups (over 50) with significant co-morbidities, such as vascular disease, congestive heart failure, renal insufficiency, or undiagnosed sleep apnea, some of these effects might have serious adverse outcomes, even over shorter time intervals. Potential for increasing growth of existing prostate cancer may be the most highly debated issue. Awareness of these potential effects, careful monitoring after initiating treatment, and cautious treatment doses may allow treatment in most age groups to be prescribed safely even when some of these diseases are present.
Problems Interpreting the Past Literature
With aging, the decline in androgens, both adrenal and testicular, is well established and appears gradual when statistical analyses are applied to large populations. However, when analyzed for individuals within this population, large variations from little change to dramatic declines are observed. The presence of disease states results in significant reduction and more rapid decline in testosterone levels in longitudinal studies than has been predicted by the statistical models derived from cross-sectional data. This observation and the growing list of medications and environmental chemicals that may further reduce testosterone levels or impact the cellular effects suggest that testosterone deficiency may be more common today than has been recognized in the past. Differences in androgen receptor sensitivity due to genetic polymorphisms, cytosine-adenine-guanine (CAG) length and wide variation in sex hormone binding globulin (SHBG) levels result in significant variations of ‘normal’ testosterone requirements between individuals.The ‘normal range’ established for populations is not a dose response curve for testosterone benefits or deficiency.
What is lacking in the currently available studies is the analysis of the ‘relative decline’ of testosterone in individuals over time and the development of disease pathologies. The ‘relative decline’ in any individual may be a more important variable than the actual testosterone level. The past studies should also be viewed with caution based on the present recognition of wide variation in testosterone levels reported utilizing different testing methods, a problem that was found in the initial Massachusetts Male Aging Study (MMAS). This is further confounded by the fact that a large percentage of testosterone production is due to peripheral conversion of adrenal precursors not represented by circulating testosterone levels, used to analyze relationships between testosterone levels and disease associations.
Future studies will need to address the circulating levels of the major androgens as well as the urinary excretion rates, which better reflect the total androgen production. Adding to the complexity of the problems of understanding pathologic correlates is the issue of estrogen conversion and the estrogen/androgen ratio, particularly related to cardiovascular diseases. Potential Benefits of Testosterone—Important New Findings
The importance of testosterone and aging disease changes is not insignificant. The lists of benefits from testosterone replacement continues to grow in significant areas that affect both the quality of life and the physiologic aspects of aging. Reported improvements in mood and cognitive function, energy, strength, bone density, and lean body mass suggest that functional capacities that increase the ability to remain independent may be improved or maintained for longer. Reduction in beta amyloid production experimentally with testosterone suggests the possibility that there may be a protective effect of replacement on the development or progression of Alzheimer’s disease, a highly important, devastating disease of aging. Newly reported relationships of testosterone deficiency to the aging diseases most likely to result in increasing healthcare costs and higher mortality rates, diabetes, hypertension, coronary artery disease (CAD), and stroke makes the issue of replacement even more critical.
The symptoms of changing sexuality, reduced libido, and erectile dysfunction (ED) have become the most widely popularized indicators of decreasing testosterone levels. The presence of ED has been associated with a two- to three-fold increased risk for both stroke and myocardial infarction (MI). Interestingly, the central arteries in the pelvic area, the heart, and the brain have endothelial nitric acid synthase (eNOS) enzymes that are more dependant on testosterone than the peripheral arteries. Improved libido and sexual function with treatment have been shown in recent studies. Additionally, improved response to phosphodiesterase inhibitors in conjunction with testosterone replacement suggests that sexuality may be maintained for longer throughout life, a clear quality of life improvement for many men and probably the single most common reason for men seeking hormone replacement from their physicians. Sexuality may, in fact, be the least important variable from a morbidity and mortality standpoint, but it can lead to increased testing and treatment that leads to these other important benefits more frequently than any other medical issue. Still, when confronted with the patient who needs treatment, the clinician is faced with the risk/benefit issue. The most highly debated of these is whether testosterone replacement may significantly increase morbidity or mortality from cardiovascular events or from prostate cancer in the older age group (over 50).