Abstract and Introduction
Abstract
The fall in testosterone levels with age appears to be a real phenomenon. Declining testicular function and hypothalamic dysregulation appear to be the mechanisms explaining the fall in testosterone levels with age. The increased prevalence of obesity and chronic illness in ageing men both cause a large drop in testosterone levels independent of ageing. Age-related hypogonadism appears to be different to other 'classical' causes of hypogonadism. Testosterone levels are not unequivocally low and associated symptoms are non-specific. In frail older men with low testosterone levels, testosterone therapy appears to improve QOL and physical function. In less frail men, however, effects of testosterone therapy in the ageing male are small and/or inconsistent. There remains an urgent need for randomised clinical trials with sufficient size, duration and power to determine specific benefits and risks of testosterone therapy in older men.
Introduction
The fall in testosterone levels with ageing has generated considerable interest among healthcare providers, the pharmaceutical industry and the general population. The clinical features of ageing and hypogonadism overlap, and it is tempting to assume that falling testosterone levels are a remediable contributor to poor life quality, frailty and premature death. The fall in testosterone levels appears to be brought about by the effects of ageing on the hypothalamic-pituitary-gonadal (HPG) axis as well as by an increasing prevalence of obesity and chronic illness. In only a small minority of ageing men do testosterone levels fall below the normal range. Whether testosterone therapy for men with late-onset hypogonadism (LOH) can ameliorate safely life quality and/or frailty remains controversial with studies failing to show consistent beneficial effects. These inconsistent data make challenging the provision of a clear explanation of potential risks and benefits of testosterone therapy.
Male hypogonadism is a clinical syndrome resulting from sub-physiological testosterone concentrations due to disruption of the HPG axis.[1,2]
Klinefelter's syndrome (KS) exemplifies hypogonadism that manifests before or during puberty. KS is a congenital chromosomal aberration (mostly 47,XXY) affecting ~0.2% of male newborns.[3] In addition to markedly low testosterone levels and elevated gonadotrophin levels (primary hypogonadism), men with KS have small testes and tend to have decreased libido, erectile dysfunction, poor beard growth, infertility (with azoospermia), tall stature, sparse pubic hair, gynaecomastia, decreased muscle mass, decreased muscle strength, low bone mineral density (BMD) and anaemia.[3] In later life, men with KS have decreased physical function, an increased risk of diabetes, obesity and bone fracture and have increased mortality.[3]
Hypogonadism that arises after puberty is exemplified by hypothalamic-pituitary disease (e.g. tumour, infiltration, trauma, radiation). In addition to low testosterone levels and low gonadotrophin levels (secondary hypogonadism), men who develop hypopituitarism after puberty tend to develop the same features as men with KS, with the exceptions of small testis, poor beard growth and abnormal height.[4]
Hypogonadism can occur also due to disruption at more than one level of the HPG axis. Opioids, for example, inhibit secretion of gonadotropin-releasing hormone (GnRH), luteinizing hormone and testosterone through action on the hypothalamus, pituitary and testis.[5]
Testosterone Levels Fall With Ageing
The European Male Ageing Study (EMAS) followed 2,736 men aged >40 for an average of 4.4 years and found a 0.1 nmol/l (0.04%) per year reduction in total testosterone concentrations and a 3.83 pmol/l (0.77%) per year reduction in free (not protein bound) testosterone concentrations.[6] Testosterone levels fall below the normal range in a minority of ageing men, however. Both EMAS and the Boston Area Community Health Survey (BACH) found that between 16 and 26% of men aged 70–79 have a total testosterone concentration that is <10.5 nmol/l compared with a proportion of between 11 and 22% of men aged <50.[7,8]
Interestingly, not all studies have observed lower testosterone levels in older men. Studies of healthy men describe no difference in testosterone concentrations between older and younger men.[9]
Age Ageing. 2015;44(2):188-195. © 2015 Oxford University Press
Copyright 2007 British Geriatrics Society. Published by Oxford University Press. All rights reserved.
