Osteoporosis and sarcopenia in older age
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
References (38)
- et al.
Epidemiology of fractures in England and Wales
Bone
(2001) - et al.
Muscle mass is more strongly related to hip bone mineral density than is quadriceps strength or lower activity level in adults over age 50 year
J Clin Densitom
(2008) Summary comments: epidemiological and methodological problems in determining nutritional status of older persons
Am J Clin Nutr
(1989)- et al.
Sarcopenia: an undiagnosed condition in older adults. Current consensus definition: prevalence, etiology, and consequences. International working group on sarcopenia
J Am Med Dir Assoc
(2011) - et al.
Consensus definition of sarcopenia, cachexia and pre-cachexia: joint document elaborated by Special Interest Groups (SIG) “cachexia-anorexia in chronic wasting diseases” and “nutrition in geriatrics”
Clin Nutr
(2010) - et al.
Prevalence of sarcopenia in community-dwelling older people in the UK using the European Working Group on Sarcopenia in Older People (EWGSOP) definition: findings from the Hertfordshire Cohort Study (HCS)
Age Ageing
(2013) - et al.
Osteoporosis in the European Union: medical management, epidemiology and economic burden. A report prepared in collaboration with the International Osteoporosis Foundation (IOF) and the European Federation of Pharmaceutical Industry Associations (EFPIA)
Arch Osteoporos
(2013) - et al.
The healthcare costs of sarcopenia in the United States
J Am Geriatr Soc
(2004) - et al.
Loss of muscle strength, mass (sarcopenia), and quality (specific force) and its relationship with functional limitation and physical disability: the Concord Health and Ageing in Men Project
J Am Geriatr Soc
(2010) - et al.
Low relative skeletal muscle mass (sarcopenia) in older persons is associated with functional impairment and physical disability
J Am Geriatr Soc
(2002)