Testosterone is vitally important for both its anabolic properties, including effects on maintaining healthy cholesterol levels, protein synthesis, muscle mass, and bone density, and its androgenic effects, including the development and maintenance of male secondary sex characteristics (deep voice, increase in facial and body hair, muscle development) and sexual functions such as libido and erectile capability.
As men age and testosterone levels decrease, classic signs of testosterone deficiency—andro-pause—frequently appear. These signs include thinning hair, decreasing libido, increasing fat mass and declining muscle mass, and even depression. It is no wonder that in the Institute of Medicine’s Testosterone and Aging,5 the authors state: “more than 1.75 million prescriptions for testosterone products were written in 2002, an estimated increase of 30 percent over the approximately 1.35 million prescriptions in 2001, and an increase of 170 percent from the 648,000 prescriptions in 1999.”
Institute of Medicine Report: A Fair Examination?
Because of both the large increase in testosterone use among men and the aging of the estimated 50-70 million members of the baby-boom generation, in 2002 the National Institute on Aging and the National Cancer Institute directed the Institute of Medicine to assess the benefits and risks of testosterone supplementation among older men. The result was a 217-page book released in November 2003. The group of physicians and scientists that authored the book reviewed a significant portion of already published material on testosterone replacement therapy, and offered its own conclusions on whether and how to conduct future studies of testosterone supplementation.
The Institute of Medicine book begins with an introduction that reviews testosterone synthesis and its action on the human body, as well as a short section on testosterone replacement therapy. This introductory section is generally factual and devoid of any overt bias, but also contains some incorrect statements. On p. 23, the authors state:
“Although some older men who have tried testosterone therapy report feeling ‘more energetic’ or ‘younger,’ testosterone supplementation remains a scientifically unproven method for preventing or relieving any physical or psychological change that men may experience as they get older.”
The following 92 pages of the book, however, detail study after study showing the efficacy of testosterone supplementation therapy in alleviating the multiple symptoms of andropause. Because of this and similar inconsistencies throughout the book, the Institute of Medicine’s findings almost certainly will be suspect in the eyes of many anti-aging researchers. This is one of the problems inherent in the authoring of books by “committees of experts.”
Photomicrograph of human testosterone hormone magnified 130x.
Testosterone Alleviates Andropause Disorders
The next section of the book, “Testosterone and Health Outcomes,” cites various studies showing that testosterone supplementation can play a significant role in alleviating many symptoms of andropause, including the loss of bone and muscle mass, depression, loss of sexual functioning, and heart disease.
This section begins by acknowledging that multiple studies have conclusively proven that testosterone levels significantly decline at a steady rate of 1-2% each year in aging men. Some of the studies cited, such as the Massachusetts Male Aging Study that examined testosterone levels in 1,709 men aged 39 to 70, showed that good health among aging men correlates with higher levels of testosterone.
Following this admission, the authors then spend the next 72 pages on an extensive review of the literature detailing how testosterone supplementation can affect many common symptoms of andropause. In the section on testosterone levels and bone mass, the authors state on p. 45:
“Several studies with large sample sizes that controlled for age and other potential confounding factors found that lower levels of bioavailable testosterone were associated with lower bone density…” and “low levels of testosterone have been identified as a risk factor for hip fractures.”
This section continues by citing literature detailing testosterone’s effect on muscle mass, body composition, and physical function. The Institute of Medicine authors correctly state that the loss of muscle mass (sarcopenia) is a significant cause of disability in the elderly, thus making the study of supplements such as testosterone all the more important. Although multiple studies show that testosterone supplementation does help aging men regain muscle mass, the Institute of Medicine still hedges on this issue, stating on p. 51 that “research findings regarding testosterone and various body composition measures have been inconsistent, although many studies find an increase in total or abdominal fat mass with decreased testosterone levels.”
One such study, which, surprisingly, is not cited by the Institute of Medicine, shows conclusively that testosterone levels are vitally important for overall physical function in aging men. Published in the Journal of Endocrinology and Metabolism, this study of 403 healthy men, aged 73 to 94 years, examined decreases in muscle strength, bone mass, and body composition seen in aging males and their relationship to falling testosterone levels.6 The researchers measured the men’s hormonal levels and ran multiple tests to gauge their body composition, muscle strength, and bone mass. Their findings were not surprising, at least to physicians well versed in anti-aging medicine—muscle strength and bone mass were at optimal levels in men with the highest levels of free testosterone. According to the authors of this independent study, “a number of clinical problems present in older men may be related to androgen [testosterone] deficiency, including reduced muscle mass, changes in body composition, and loss of BMD [bone mass density].”
Low Testosterone Tied to Health Disorders
While optimal testosterone levels are needed to maintain muscle mass and bone strength, testosterone also is needed for cognition, sexual functioning, and even heart health. Multiple studies have confirmed that men who maintain optimal testosterone levels as they age have significantly fewer symptoms of mental senility when compared to men with low levels of testosterone.
The Institute of Medicine book confirms this and cites three widely publicized, randomized, placebo-controlled studies showing that testosterone supplementation improves verbal memory, working memory, and visuospatial performance in elderly men.7-9 Unfortunately, the Institute of Medicine omits a landmark study published in 2002 in which 407 men, aged 50 to 91, were followed for 10 years and had multiple tests to determine their testosterone levels and cognitive functioning.10 The authors of this independent study concluded:
“Higher FTI [free testosterone levels] was associated with better scores on visual and verbal memory, visuospatial functioning, and visuomotor scanning and a reduced rate of longitudinal decline in visual memory.”
An even more recent study also overlooked by the Institute of Medicine shows that elderly men who suffered from Alzheimer’s disease had lower-than-expected levels of testosterone, which the authors hypothesize may be due to brain degeneration seen in Alzheimer’s sufferers.11 The study authors are now investigating whether low testosterone levels precede cognitive dysfunction in men at risk for Alzheimer’s. If they do, then testosterone replacement therapy could be warranted for men with lower-than-normal testosterone levels to potentially ward off Alz-heimer’s disease.
Testosterone supplementation has been shown in multiple studies to improve libido12,13 and erectile capability14 when administered to aging men. Given basic scientific knowledge of how testosterone plays a key role in men’s sexual development during puberty and functioning during adulthood, results such as this should come as no surprise. The Institute of Medicine, however, only grudgingly acknowledges the role that testosterone supplementation can play in improving sexual performance in men, stating on p. 70 that “overall, there is some suggestion that testosterone therapy may be beneficial [in terms of sexual functioning] to men with low baseline testosterone levels.”
The Institute of Medicine book includes a brief, three-page section (pp. 77-80) on the possible effects of testosterone and heart health in aging men. With cardiovascular disease being the number-one killer of men in the US and most Western industrialized nations, it is surprising that the Institute of Medicine does not give this very important topic more consideration. As in other sections of the book, the authors overlook studies showing the beneficial effects of testosterone on heart disease, such as the Rotterdam Study, in which researchers examined testosterone levels and cardiac health among 504 men aged 67 to 75. The researchers conclusively showed that men with higher levels of testosterone had lower levels of coronary artery disease.15 The Rotterdam researchers concluded:
“We found an independent, inverse association between levels of endogenous testosterone and severe aortic atherosclerosis and progression of aortic atherosclerosis in men.”
It is a mystery why the Institute of Medicine would exclude such a well-designed study and state on p. 77 that “heart and vascular diseases have a complex multifactorial etiology, and the role of testosterone in this mix has yet to be determined.”