PMC:4159494 / 3826-10971 JSONTXT

{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/4159494","sourcedb":"PMC","sourceid":"4159494","source_url":"https://www.ncbi.nlm.nih.gov/pmc/4159494","text":"Definition and assessment of abnormal body composition phenotypes: osteopenia/osteoporosis, sarcopenia, and obesity\n\nOsteopenia/osteoporosis\nOsteopenia/osteoporosis is a skeletal disorder characterized by compromised bone strength leading to increased risk of fractures. Osteoporosis affects approximately 12 million adults over the age of 50 years in the USA [4]. In 2005, more than 2 million incident fractures were reported in the USA alone, with a total cost of $17 billion. Even if rates stay the same, the aging of the world population is expected to increase the number of fractures and costs in the USA by 48 % to greater than 3 million fractures associated with a cost of $25.3 billion [5].\nAlthough osteoporosis is a complex entity, we can measure areal bone mineral density (BMD), which is used as a proxy to define bone strength and to diagnose osteopenia/osteoporosis [6, 7]. Dual-energy X-ray absorptiometry (DXA) is the most common diagnostic imaging technique for assessing BMD. DXA uses low-radiation X-rays of two different photon energy levels that pass through the body and are identified by a photon detector that measures the amount of energy absorbed by soft tissue and bone at each pixel [8]. This method measures both bone and soft tissue [8]. Soft tissue is further subdivided into fat and lean [also called lean body mass (LBM), Table 1] based on the empiric attenuation of both pure fat and bone-free soft tissue [9]. Therefore, bone mineral content and BMD, as well as fat and fat-free soft tissues at the whole-body and regional levels can be assessed by DXA [8, 10]. Uniform standards for diagnosing osteopenia and osteoporosis by DXA do exist. According to the World Health Organization (WHO), the operational definition of osteopenia is a BMD that lies from 1.1 to 2.4 standard deviations below (a T-score of 1.1–2.4) and osteoporosis is a BMD that lies 2.5 standard deviations or more below the average value for young healthy women (a T-score of \u003c −2.5). Increased BMD augments the strength of bone. On the contrary, significant losses in BMD predispose an individual for increased risk of fracture.\nTable 1 Body composition terminology\nASM (appendicular skeletal muscle mass) Lean body mass from limbs, a surrogate measure of skeletal muscle mass. It can be expressed adjusted for height in squared meters (kg/m2) and named ASM index.\nFFM (fat-free mass) Sum of LBM plus bone mineral content\nFM (fat mass) Amount of fat, also known as body fat\nLBM (lean body mass) Also called lean soft tissue, it is the sum of the lean compartments of the body (excluding bone mineral content) (total body water, total body protein, carbohydrate, nonfat lipid, and soft tissue minerals)\nObesity Body mass index ≥ 30 kg/m2\nOsteosarcopenic Obesity Concurrent osteoporosis, low muscle mass, and obesity\nSarcopenia Low skeletal muscle mass or muscle wasting\nSarcopenic obesity Concurrent obesity and low muscle mass\n\nSarcopenia\nMuscle and bone mass, as well as their strength/quality, are both lost during aging starting in the late 20s and accelerating in the 50s [11–13]. In the presence of chronic disease, drug therapy, environmental factors, poor nutrition, and physical inactivity, this loss can be accelerated.\nOne important advantage of using DXA is its ability to estimate appendicular skeletal muscle (ASM) mass which is of particular interest for the assessment of sarcopenia. ASM corresponds to the amount of LBM in the arms and legs, which is mainly muscle (except for a small amount of connective tissue and skin) [14].\nSarcopenia is a term originally used to describe age-related decreases in muscle mass [15]. The term has evolved to indicate a point where skeletal muscle mass and/or strength has declined past a threshold in which health is affected. The European Consensus [16] has recently defined sarcopenia as a progressive, generalized loss of muscle mass and strength which will increase the risk for physical disability, diminished physical performance, and poor quality of life. Although losses of both muscle mass and strength can occur simultaneously, this relationship is not linear [16–18].\nAlthough there are several working definitions of sarcopenia, one of the most commonly used criteria is a level of skeletal muscle mass (ASM index, Table 1) lower than 2 SD below the expected mean for healthy young adults, as established by DXA. This sex-specific definition corresponds to ≤7.26 kg/m2 for men and ≤5.45 kg/m2 for women [19]. Importantly, individuals below this cut point have a significantly increased risk of adverse functional status, such as higher risk of disability, falls, and fractures [20].\nIt is important to highlight that establishing the threshold to define sarcopenia has been a challenge for the past several years. A variety of cut points in the literature have been reported, which were developed using different body composition techniques such as DXA, bioelectrical impedance, skinfold thickness measurements, and computerized tomography (CT images) [21]. Although most cut points are based on measurements of muscle mass, muscle quality has also been used as a criterion to identify sarcopenia. Measurements of muscle strength (handgrip, hip, or knee strength) are popular for this purpose because of their cost-effectiveness and availability in clinical settings [22]. In summary, definitions of sarcopenia are somewhat arbitrary and are limited to the availability of large clinical and epidemiological studies (population-representative cut points) using gold-standard body composition assessment tools [23]. The reader is referred to an extensive review on the topic for an in depth discussion [24].\n\nObesity\nObesity is a condition of excess weight, specifically adipose tissue, in the body. The most commonly accepted definition of obesity is the WHO categories of BMI [weight (kg)/height (m2)] of 30 kg/m2 or higher. According to this definition, there are three grades of obesity: grade I (BMI 30.0–34.9 kg/m2), grade II (BMI 35.0–39.9 kg/m2), and grade III (BMI ≥ 40 kg/m2) [25]. Nonetheless, BMI is an imperfect and controversial criterion [26] since it does not differentiate between lean and fat tissues. Using percent body fat is another way to classify individuals as obese. Normal percent body fat for an adult man is considered to be approximately 12–20 % of total body weight and 20–30 % for an adult woman [27]. Alternatively, the WHO has suggested that obesity is identified at levels of higher than 25 % body weight for men and 35 % for women [28], with somewhat higher levels established for elderly individuals (\u003e28 % for men and \u003e40 % for women) [29]. Percent body fat values for obese individuals separated by sex, age, and ethnicity have also been proposed by Gallagher et al. [30]. Interestingly, the distribution of body fat is also associated with increased health risks, with android adiposity being more problematic compared to the gynoid adiposity. These are most easily identified with waist circumference measures (\u003e88 cm for men and \u003e102 cm for women) [27, 31] or a waist to hip ratio calculation (\u003e0.90 for men and \u003e0.80 for women) [32].","divisions":[{"label":"title","span":{"begin":0,"end":115}},{"label":"sec","span":{"begin":117,"end":2932}},{"label":"title","span":{"begin":117,"end":140}},{"label":"p","span":{"begin":141,"end":699}},{"label":"p","span":{"begin":700,"end":2932}},{"label":"table-wrap","span":{"begin":2135,"end":2932}},{"label":"label","span":{"begin":2135,"end":2142}},{"label":"caption","span":{"begin":2143,"end":2171}},{"label":"p","span":{"begin":2143,"end":2171}},{"label":"table","span":{"begin":2172,"end":2932}},{"label":"tr","span":{"begin":2172,"end":2370}},{"label":"td","span":{"begin":2172,"end":2211}},{"label":"td","span":{"begin":2212,"end":2370}},{"label":"tr","span":{"begin":2371,"end":2427}},{"label":"td","span":{"begin":2371,"end":2390}},{"label":"td","span":{"begin":2391,"end":2427}},{"label":"tr","span":{"begin":2428,"end":2479}},{"label":"td","span":{"begin":2428,"end":2441}},{"label":"td","span":{"begin":2442,"end":2479}},{"label":"tr","span":{"begin":2480,"end":2707}},{"label":"td","span":{"begin":2480,"end":2500}},{"label":"td","span":{"begin":2501,"end":2707}},{"label":"tr","span":{"begin":2708,"end":2742}},{"label":"td","span":{"begin":2708,"end":2715}},{"label":"td","span":{"begin":2716,"end":2742}},{"label":"tr","span":{"begin":2743,"end":2820}},{"label":"td","span":{"begin":2743,"end":2766}},{"label":"td","span":{"begin":2767,"end":2820}},{"label":"tr","span":{"begin":2821,"end":2874}},{"label":"td","span":{"begin":2821,"end":2831}},{"label":"td","span":{"begin":2832,"end":2874}},{"label":"tr","span":{"begin":2875,"end":2932}},{"label":"td","span":{"begin":2875,"end":2893}},{"label":"td","span":{"begin":2894,"end":2932}},{"label":"sec","span":{"begin":2934,"end":5677}},{"label":"title","span":{"begin":2934,"end":2944}},{"label":"p","span":{"begin":2945,"end":3234}},{"label":"p","span":{"begin":3235,"end":3550}},{"label":"p","span":{"begin":3551,"end":4137}},{"label":"p","span":{"begin":4138,"end":4653}},{"label":"p","span":{"begin":4654,"end":5677}},{"label":"title","span":{"begin":5679,"end":5686}}],"tracks":[{"project":"2_test","denotations":[{"id":"24740742-11115784-56351029","span":{"begin":6398,"end":6400},"obj":"11115784"},{"id":"24740742-11115784-56351030","span":{"begin":7060,"end":7062},"obj":"11115784"}],"attributes":[{"subj":"24740742-11115784-56351029","pred":"source","obj":"2_test"},{"subj":"24740742-11115784-56351030","pred":"source","obj":"2_test"}]}],"config":{"attribute types":[{"pred":"source","value type":"selection","values":[{"id":"2_test","color":"#ac93ec","default":true}]}]}}