Elsevier

Bone

Volume 80, November 2015, Pages 126-130
Bone

Osteoporosis and sarcopenia in older age

https://doi.org/10.1016/j.bone.2015.04.016Get rights and content

Highlights

  • Osteoporosis has been clearly defined and fracture risk prediction tools allow accurate evaluation of the likelihood of adverse outcomes.

  • Although several consensus definitions of sarcopenia have been suggested, none have been universally adopted.

  • A universal definition of sarcopenia is required to facilitate advancement of research in this area.

Abstract

Osteoporosis and sarcopenia are common in older age and associated with significant morbidity and mortality. Consequently, they are both attended by a considerable socioeconomic burden. Osteoporosis was defined by the World Health Organisation (WHO) in 1994 as a bone mineral density of less than 2.5 standard deviations below the sex-specific young adult mean and this characterisation has been adopted globally. Subsequently, a further step forward was taken when bone mineral density was incorporated into fracture risk prediction algorithms, such as the Fracture Risk Assessment Tool (FRAX®) also developed by the WHO. In contrast, for sarcopenia there have been several diagnostic criteria suggested, initially relating to low muscle mass alone and more recently low muscle mass and muscle function. However, none of these have been universally accepted. This has led to difficulties in accurately delineating the burden of disease, exploring geographic differences, and recruiting appropriate subjects to clinical trials. There is also uncertainty about how improvement in sarcopenia should be measured in pharmaceutical trials. Reasons for these difficulties include the number of facets of muscle health available, e.g. mass, strength, function, and performance, and the various clinical outcomes to which sarcopenia can be related such as falls, fracture, disability and premature mortality. It is imperative that a universal definition of sarcopenia is reached soon to facilitate greater progress in research into this debilitating condition.

This article is part of a Special Issue entitled “Muscle Bone Interactions”.

Introduction

Osteoporosis and sarcopenia are common diseases that predominantly affect older individuals [1], [2]. They are both associated with significant morbidity and can therefore lead to considerable health and social costs [3], [4]. Specially, sarcopenia is associated with increased rates of disability, poor mobility, frailty, and hospitalisation [5], [6] and it has been estimated that, in the United States, sarcopenia resulted in additional healthcare costs of over $18 billion in 2001 [4]. Furthermore, in common with hip and vertebral fracture fractures, a decline in muscle health has also been shown to predict future mortality from middle-age into later life [7]. Given current secular trends in population demographics with greater longevity, the burden of both osteoporosis and sarcopenia may continue to increase.

In addition to the similar population in which they occur, there is also growing evidence of a link between the two conditions. Studies have shown associations between bone and muscle health by dual energy X-ray absorptiometry (DXA) and more recently using cross-sectional imaging techniques [8], [9]. DXA studies have focussed on relationships between facets of muscle health and either bone mass or density and have tended to show positive relationships [10], [11], [12]. The use of peripheral quantitative computed tomography (pQCT) has additionally shown bone size and strength to be associated with muscle size, and to a lesser extent, muscle strength. Relationships of muscle with cortical and trabecular volumetric bone mineral density (vBMD) have been less consistent [8], [9].

There are several potential explanations for these interrelationships (Fig. 1). The mechanostat hypothesis describes the action of muscle contraction providing a direct mechanical stimulus to bone which promotes osteogenesis [13]. Hormones, such as growth hormone, can have positive effects on the growth of muscle and bone [14], [15]. Furthermore, exercise and levels of activity clearly augment both of these components of the musculoskeletal system. There are also likely to be common genetic and developmental components to muscle and bone health [16], [17].

Despite their similarities and interrelationships, study into these diseases is at very different stages of evolution, with research into osteoporosis considerably ahead. This review describes the progress that has been made in defining these conditions and explores the reasons for the discrepancy in progress made.

Section snippets

The history of osteoporosis

Osteoporosis is a skeletal disease characterised by low bone mass and microarchitectural deterioration of bone tissue with a consequent increase in bone fragility and susceptibility to fracture [18]. The term literally means “porous bone” and was first introduced in France and Germany when it described a histological diagnosis. We now know this to represent bone tissue which is normally mineralised but reduced in quantity. This abnormality is the mechanism through which bones become weaker,

The history of sarcopenia

The term sarcopenia was first coined in 1989 by Irwin Rosenberg who used it to pertain to the loss of muscle mass with age [28], [29]. It has since become apparent that muscle function, in addition to muscle mass, is necessary to describe sarcopenia and so the definition has undergone an evolution to reflect this. Although muscle mass would intuitively be thought to be the central factor, it is only weakly associated with function and disability. It does, however, relate to low muscle strength

The importance of defining sarcopenia

As sarcopenia is associated with significant morbidity and is a predictor of premature mortality, it is clearly important for further research in this area to take place. A universal consensus definition of sarcopenia would allow an evaluation of prevalence across different geographical areas. This would allow a more accurate quantification of the burden of disease and, as in the case of osteoporosis, potentially provide further clues to the aetiology. It would also allow identification of

Difficulties in defining sarcopenia

When a definition of sarcopenia is developed in clinical practice, it is important that it is practical, affordable, and acceptable to patients. Although it may be possible to use a more complicated and expensive method within research, it would be favourable to have a definition that could be used in both settings allowing results of studies to be more easily translatable into clinical practice.

The principal reason that progress in sarcopenia research has not advanced as rapidly as

Conclusion

There are many similarities between osteoporosis and sarcopenia including patient demographics, high prevalence, and great socioeconomic cost. There is also evidence of a mechanistic interrelationship between muscle and bone with sarcopenic individuals at greater risk of osteoporosis and vice versa. Although both are well recognised, there is a considerable difference in the progress that has been made in managing the two conditions.

A universal definition was established for osteoporosis in

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