Body Composition, Metabolic Syndrome and Testosterone in Aging Men

C A Allan; B J G Strauss; R I McLachlan

Disclosures

Int J Impot Res. 2007;19(5):448-457. 

In This Article

Abstract and Introduction

Abstract

The ageing process in men is marked by changes in body composition (loss of fat-free mass (FFM) and skeletal muscle, and gain in fat mass (FM)) and is associated with a decline in serum testosterone. Correlations between these aspects of ageing and the acknowledged role of exogenous testosterone in reversing the loss of FFM and gain in FM seen in adult men with congenital or acquired hypoandrogenism have led to the hypothesis that testosterone therapy in ageing men will result in favourable changes in body composition and may improve metabolic status and/or cardiovascular risk. Data from randomized controlled trials of testosterone therapy in ageing men addressing the endpoints of body composition and components of the metabolic syndrome and cardiovascular risk factors are reviewed, and the impact of the increasing prevalence of obesity on these relationships is considered.

Introduction

As men age beyond 40 years, they experience a decline in serum testosterone. The rate of fall in testosterone has been well documented in cross-sectional[1,2] and longitudinal[3,4] studies and is estimated to be 1--2% per annum, excluding the further impact of other variables such as ill health or concomitant medications,[1,5] and possibly environmental factors.[6]

The age-related fall in testosterone may impact the physical, sexual and/or psychological domains of a man's health; however, the relationship between ageing, declining sex steroids and symptomatology is complex. In particular, symptoms related to well being are often of a nonspecific nature.[7] As androgens are known to be important determinants of body composition, this provides an objective parameter by which to examine the impact of declining testosterone levels in ageing men.

Serum testosterone levels correlate positively with fat-free mass (FFM) and negatively with fat mass (FM),[8] and hypoandrogenism in young men is associated with a decline in FFM and skeletal muscle.[9] Testosterone replacement therapy increases FFM and decreases FM in men with acquired hypogonadism and hypoandrogenism due to ageing.[10,11] Furthermore, muscle mass has been shown to correlate with strength (as measured by dynamometry) in healthy older men,[12] and in turn strength has been shown to positively correlate with bioavailable testosterone.[13] This has led to interest in the hypothesis that testosterone supplementation may attenuate or even reverse age-associated sarcopaenia and enhance the physical strength and well being of older males. Also, because of the integral nature of the relationship between body composition, and visceral fat in particular, and metabolic health, change in FM is an important outcome measure when considering the role of testosterone therapy in this cohort. In this context, there is growing recognition of the need to define the role played by testosterone in the metabolic status of men as they age.

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