Dose-Response Relationships Between Gonadal Steroids and Bone, Body Composition, and Sexual Function in Aging Men

Area of Science:

• Endocrinology and Metabolism
• Gerontology
• Men's Health

Background:

• Current lower limit of normal for testosterone is based on the 2.5th percentile, which doesn't account for physiological changes.
• Understanding dose-response relationships is crucial for defining optimal testosterone levels in older men.

Purpose of the Study:

• To investigate the relationship between testosterone concentrations and various physiological measures in older men.
• To characterize dose-response effects of testosterone on bone resorption, body fat, and sexual function.

Main Methods:

• 177 men aged 60-80 received varying doses of testosterone gel or placebo for 16 weeks.
• Measurements included serum C-telopeptide (CTX), total body fat (DXA), and self-reported sexual desire.
• Goserelin acetate was used to suppress endogenous testosterone production.

Main Results:

• Significant changes in serum CTX, body fat, and sexual desire were observed at various testosterone levels.
• Bone resorption markers changed even at testosterone levels of 0-99 ng/dL.
• Sexual desire and erectile function remained similar to controls until testosterone levels dropped below 100 ng/dL.

Conclusions:

• Physiological changes related to testosterone occur across a wide range of concentrations, often below current normal ranges.
• Existing methods for establishing normal testosterone ranges may not adequately reflect functional changes in older men.
• Novel approaches are needed to define testosterone's normal range, considering individual physiological responses.