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News — A new study reveals that relatively few men, only 5.6 percent of the male population, actually suffer from low testosterone accompanied by clinical symptoms. That percentage, however, rises substantially with age.

Low testosterone levels are typically defined as less than 300 ng/dL (nanograms per deciliter) of total testosterone and less than 5 ng/dL of free testosterone. Free testosterone is the amount of the hormone unbound to other proteins and is "free" to work inside the body. "Low levels of testosterone impact many aspects of male physiology," said Andre B. Araujo, Ph.D., a research scientist at the New England Research Institutes in Watertown, Mass., and lead author of the study. "This is particularly significant because the ongoing aging of the U.S. male population is likely to cause the number of men suffering from androgen deficiency to increase appreciably."

Consistent with a recently issued Clinical Practice Guideline from the Endocrine Society, symptomatic androgen deficiency in the study by Araujo and colleagues is defined as low total and free testosterone plus the presence of low libido, erectile dysfunction, osteoporosis or facture, or two or more of the following symptoms: sleep disturbance, depressed mood, lethargy, or diminished physical performance.

For this study, the researchers analyzed data on 1,475 randomly selected men enrolled in the Boston Area Community Health (BACH) Survey. The survey tracked subjects between the ages of 30-79 and compiled complete data on factors such as testosterone, symptoms of hormone deficiency, and medications that may impact sex hormone levels. Among all men in the study (mean age 47.3 plus-or-minus 12.5 years), approximately 24 percent had low total testosterone and 11 percent had low levels of free testosterone. Interestingly, while low testosterone levels were associated with symptoms, many men with low testosterone levels were asymptomatic (e.g., among men aged 50 years and older 47.6 percent were asymptomatic).

"Since these men would not likely come to clinical attention," said Araujo, "it may be important to determine whether there are clinical risks to missing these asymptomatic men with low testosterone levels." Overall, only 5.6 percent of men in the study had symptomatic androgen deficiency. For those men in the upper range of ages in the study (70 years or older), however, the percentage increased to 18.4 percent.

The researchers predicted that by the year 2025 there may be as many as 6.5 million American men 30-79 years of age with symptomatic androgen deficiency, an increase of 38 percent from year 2000 population estimates.

"This study did not assess whether men with symptomatic androgen deficiency are good candidates for testosterone therapy," said Araujo. "Well designed randomized placebo-controlled trials would be needed to address the risks and benefits of testosterone therapy."

The BACH Survey was supported by the National Institute of Diabetes and Digestive and Kidney Diseases (Grant DK 56842). Analyses for the current study were supported through an unrestricted educational grant from GlaxoSmithKline.

A rapid release version of this paper has been published on-line and will appear in the November 2007 issue of the Journal of Clinical Endocrinology & Metabolism, a publication of The Endocrine Society.

Founded in 1916, The Endocrine Society is the world's oldest, largest, and most active organization devoted to research on hormones, and the clinical practice of endocrinology. Today, The Endocrine Society's membership consists of over 14,000 scientists, physicians, educators, nurses and students in more than 80 countries. Together, these members represent all basic, applied, and clinical interests in endocrinology. The Endocrine Society is based in Chevy Chase, Maryland. To learn more about the Society, and the field of endocrinology, visit our web site at .