REVIEWSarcopenic obesity: A new category of obesity in the elderly
Introduction
The prevalence of obesity in the elderly has dramatically increased in recent years, rising in the United States to nearly 30% in men, and in women aged 60 years and over increases in extreme obesity [1]. Realistic predictions suggest that by 2010 the prevalence of obesity in the over sixties could rise to 33.6% as a best-case and to 39.6% as a worst-case scenario [2]. Since both ageing and obesity may have a heavy impact on public health, an increasingly obese elderly population will undoubtedly represent a growing financial problem in the health care system in developed countries [3].
Weight gain and ageing exert divergent effects on fat sub-compartments (Table 1). Normal ageing is associated with a progressive increase in fat mass, which normally peaks at about age 65 years in men and later in women [4]. Body fat distribution also changes with age, with visceral abdominal fat increase and subcutaneous abdominal fat decrease [5], [6]. These changes occur even when there are no significant changes in body mass index (BMI) and have important consequences on the profile of metabolic and cardiovascular risk factors.
The loss of muscle mass that occurs with ageing is well documented and appears to occur even in relatively weight stable healthy individuals [7]. Several mechanisms underlying age-related muscle loss have been recognized including neuronal [8], hormonal changes [9], poor nutrition [10], physical inactivity [11] and low-grade inflammation [12], [13]. With ageing, significant decline in muscle strength, even after adjusting for muscle mass, has been documented [8], [14] as well as muscle quality decline, characterized by a decrease in fibre size and number, preferential loss of type II fibres, decreased synthesis of muscle protein and reduced mitochondrial function [14], [15]. Computed tomography Scans at the mid thigh level have also highlighted increases in the amount of fat within and around muscles (Fig. 1) [16]. Thus, ageing involves body fat and muscle shifting to more fat and less muscle.
Age-related body composition changes and the increased prevalence of obesity in the elderly produce a combination of excess weight and reduced muscle mass and/or strength, which has recently been defined as sarcopenic obesity (SO) [3].
Obesity and sarcopenia in the elderly may potentiate each other and maximize their effects on physical disability, morbidity and mortality. Obese elderly people with inadequate muscle mass may represent the worst aspects of both conditions, resulting in a higher risk of reducing their likelihood of being free from disability.
Developed countries will likely face an increasing burden due to SO in the elderly.
Section snippets
Definition of sarcopenic obesity
The definition of SO necessarily combines those of sarcopenia and obesity. A few definitions of sarcopenia have been proposed in recent years; some consider total muscle mass, while others consider appendicular skeletal muscle mass (corresponding to the sum of skeletal muscle from the arms and legs) and use different methods to account for body size [17], [18], [19], [20]. Measurement of muscle mass requires the use of techniques not commonly used in clinical practice: Dual Energy X-Ray
Pathogenesis
Age-related body composition changes (i.e. muscle mass decline and fat mass increase) seem to be strongly connected each other from a pathogenetic point of view.
Age-related decreases in muscle mass and muscle strength, in combination with reduced endurance, may determine reduced physical activity [14]. A reduction in muscle mass and physical activity reduces total energy expenditure in elderly people and may lead to weight gain, characterized mainly by the accumulation of abdominal fat [14].
On
Clinical implications of sarcopenic obesity
Self-reported mobility capacity is markedly diminished in the overweight and obese compared with lean elderly adults [44], [45], [46]. It has been shown that BMI is inversely related to measured physical performance in older people [45] and that a BMI higher than 30 is predictive of a decline in functional status and future disability [44].
It is intuitive that having high levels of fat mass together with low muscle mass may lead to more functional limitations, as well as to more metabolic
Treatment
Several studies addressed the treatment of sarcopenia in the elderly [57], [58], [59]. Hormonal replacement (testosterone, dehydroepiandrosterone and growth hormone) has been proposed to reverse age-related muscle mass and strength loss, with inconsistent results [57]. Furthermore these approaches, even though theoretically correct, require caution because of possible detriment to other tissues or because of possible pathological growth promotion [57], [59]. Resistance training seems to be the
Future directions
The loss of muscle mass and the gain in fat seem to be linked to each other across ageing and contribute, together with positive energy balance, to the development of SO.
Identification of elderly subjects with SO could be relevant in clinical practice because it may identify a group of subjects with particularly great health risk, and the concept of SO may help to clarify the relationship between obesity, morbidity and mortality in the elderly.
Both sarcopenia and obesity have been shown to be
Acknowledgements
This study was supported by grants from the MIUR project “Aging Effects on Adipose Tissue Production of Inflammatory Peptides” 2005-063885-005.
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