From the Chicago MeetingsSarcopenia☆,☆☆
Section snippets
Epidemiologic studies
The New Mexico group has developed methods for estimating the prevalence of sarcopenia and associations with risk factors and consequences in two studies of community-dwelling elderly populations in New Mexico. The first study is the New Mexico Aging Process Study, which consists of a cohort of approximately 400 elderly men and women who are being followed over time for the onset of sarcopenia, falls, morbidity, impairment, and disability.13 The second study is the New Mexico Elder Health
Future directions
These data suggest that many of the deleterious health and functional sequelae of old age are concentrated in a small group of people with sarcopenic-obesity. Because sarcopenic-obese, elderly individuals have increased body fat that masks their sarcopenia, they may not be recognized as “frail” unless muscle mass and strength are additionally measured.
Sarcopenia, obesity, and sarcopenic-obesity may be considered “syndromes of disordered body composition” that have different associations with
Age-related changes in muscle
Muscle accounts for approximately 40% of the total body mass and 75% of the body's cell mass.18 A quarter of all protein synthesis in the body occurs in muscle. There is a decrease in muscle mass and muscle strength with aging.19 In addition, there is a decline in age-related muscle efficiency (ie, muscle strength per unit of muscle mass).19, 20 This appears to be related to a decrease in total muscle fitness with aging with a disproportionate atrophy of the type IIa (fast-twitch) muscle fibers.
The role of cytokines in the development of sarcopenia
Loss of muscle with age may be caused by loss of anabolic factors such as neural growth factors, growth hormone, androgens and estrogens, and physical activity; by an increase in catabolic factors such as inflammatory cytokines; or by a combination of the two. The last is the most likely, but relatively little is currently known about the contribution of cytokines to the development of sarcopenia. It is clear that several of the cytokines are capable of causing muscle amino acid export in vivo
Anorexia of aging and sarcopenia
It is now well established that food intake declines with aging both in the general population and in highly healthy persons.51 The decline in food intake is greater in males than in females. The reasons for this physiologic decline in food intake are multiple and are reviewed briefly below. The role of this physiologic anorexia of aging in the pathogenesis of sarcopenia is uncertain.
The regulation of food intake is complex and involves both peripheral and central mechanisms.52 The major reason
Other nutritional factors and sarcopenia
There is now excellent evidence that homocystine levels increase with aging91 and that elevated homocystine levels are correlated with atherosclerosis.92 Peripheral vascular disease is associated with decreased lower limb function.93 Atherosclerosis is associated with accelerated blood flow to muscles and metabolic efficiency of muscles.94 Although deficiencies of both vitamin B12 and folate are associated with elevated homocystine level,95 it appears that they do not account for the majority
Hormones and sarcopenia
Both testosterone99, 100 and the adrenal androgens101 decline with age. There is epidemiologic evidence supporting the relationship of the fall in testosterone with the decline in muscle mass,17 muscle strength,17, 102 and functional status102 with aging. Interventional studies with testosterone have demonstrated an increase in muscle mass103 and an increase in upper arm strength.58, 104 One study suggested an increase in lower limb strength, but the study was not placebo controlled.105 Another
Exercise and sarcopenia
It is now well established that exercise, particularly that which increases mechanical force by strength training (resistance exercise), can increase muscle mass and strength even in very elderly persons.110 In elite Olympic oarsmen there was a decline in VO2 and in peak power. This decline was attenuated to some extent in those who continued to do regular aerobic training.111 Nelson et al112 demonstrated that high-intensity strength training exercises are an effective and feasible means to
Conclusion
The loss of muscle mass with aging represents a major cause of functional decline and disability. There is a paucity of data examining the pathogenesis of sarcopenia in older persons. The available data suggest that the pathogenesis of sarcopenia is multifactorial (Fig 5).Intrinsic aging changes in the muscle and nerve represent one set of causes, but poor nutritional status, a decline in anabolic hormones and cytokines, and atherosclerosis all appear to
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Supported in part by USDA Cooperative Agreement 58-1950-9-001 and National Institutes of Health Grant AG15797. The contents of this publication do not necessarily reflect the views or policies of the US Department of Agriculture, nor does mention of trade names, commercial products, or organizations imply endorsement by the US Government.
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Reprint requests: John E. Morley, MB, BCh, Department of Medicine/Geriatrics, Saint Louis University School of Medicine, 1402 South Grand, Room M-238, St Louis, MO 63104.