Sarcopenia

Sarcopenia is the loss of skeletal muscle mass and strength with age.1 It is common in men and women, with prevalence ranging from 9% to 18% over the age of 65. Recognition of its serious health consequences in terms of frailty, disability, morbidity, and mortality is increasing. The estimated direct healthcare cost attributable to sarcopenia in the United States in 2000 was $18.5bn (£11.9bn; €14.2bn), about 1.5% of total healthcare expenditure for that year.2 In May 2010, the European Working Group on Sarcopenia in Older People published consensus guidelines on the definition and diagnosis of sarcopenia.3

What should clinicians look for? Well recognised risk factors for sarcopenia include increasing age, low levels of physical activity, inadequate nutrition, and comorbidity, such as type 2 diabetes.4 Identifying high risk groups of older people is straightforward, but making a diagnosis is more difficult. In the European guidelines, sarcopenia is diagnosed firstly on the basis of impaired physical performance, characterised by slow gait speed, and then either by low muscle strength assessed by handheld dynamometry or low muscle mass measured, for example, by bioimpedance.

This comprehensive approach is well suited to research and specialist clinical settings but may be challenging in primary care. Hand grip strength alone has also been advocated as a clinical marker of sarcopenia that is simple and cost effective and has good predictive power,5 although it does not provide comprehensive information. The feasibility and acceptability of alternative approaches to diagnosing sarcopenia in different healthcare settings are not yet established.

In terms of managing sarcopenia, meta-analyses show that resistance exercise can improve muscle mass and strength in older adults.6 7 A systematic review concluded that progressive resistance strength training improved physical functioning in older people, including the performance of some simple and complex activities. However, caution was advised in applying the results in practice because adverse events were not adequately reported.7

The evidence for the role of nutrition in the prevention and treatment of sarcopenia is less clear. In particular, more information is needed on protein and specific amino acids, such as leucine. Although protein intake may become insufficient with the reduction in total food intake seen in later life and dietary reference intake for protein may be set too low to ensure optimal intake in healthy older adults, attempts to improve muscle mass and function with protein supplementation have had variable results. Similarly, findings from observational studies and randomised controlled trials reporting the effects of vitamin D on muscle strength have not been consistent, although some do report benefit.8 9 Interest in the role of antioxidants is also increasing.

Other approaches to treating sarcopenia have focused on targeting the age related decline in key hormones. Testosterone replacement in older hypogonadal men modestly increases muscle mass and strength, and growth hormone seems to affect mass more than strength. However, evidence that these benefits translate into improved physical performance is less clear. There has also been recent interest in the use of angiotensin converting enzyme inhibitors and β blockers. New treatments currently being developed include myostatin inhibitors and cytokine inhibitors.10

Despite recent progress in understanding sarcopenia, unexplained variation is seen in both muscle mass and strength in older people, and a life course model of sarcopenia has been proposed. The model proposes that muscle mass and strength in later life may reflect not only the current rate of muscle loss but also the peak attained earlier in life. To date most observational and intervention studies of sarcopenia have focused on modifying decline in later life, but a life course approach would include factors that operate earlier in life, such as those that influence early growth and development.11

Epidemiological evidence linking low birth weight with lower muscle mass and strength in later life is strong and consistent with replication in children, young adults, and older adults. However, the underlying mechanisms remain to be explored, and we have no evidence to date for the benefit of interventions instituted earlier in life. These are important areas for future research. Sarcopenia is firmly on the agenda for research into ageing and now needs to be recognised in routine clinical practice.