Sarcopenia is common, and is a global, socio-economic, healthcare problem. But what is it?
What is sarcopenia?
Derived from the Greek words sarx (flesh) and penia (loss), sarcopenia, the loss of skeletal muscle mass and function with age, is now recognised as a major clinical problem for older people. The processes involved in sarcopenia are complex but involve age related muscular, hormonal and neural changes. For example the decline in the concentration of certain hormones can have a negative impact on muscle quality (power, speed and elasticity) and reduction in the muscle cells involved in regenerating muscle fibre.
How common is it?
Prevalence estimates of sarcopenia rise from 12% for 60-70 year olds to 30% for 80+ year olds. The most recent UK study in older adults living in the community (average age 67) estimated sarcopenia affected 4.6% men and 7.9%, but prevalence may be as high as 1 in 3 frail older people living in nursing homes. There is growing recognition of its serious health consequences, even in moderate sarcopenia, in terms of increased risk of frailty, limited mobility, increased falls, morbidity and mortality. Sarcopenia has even been described as organ failure (muscle insufficiency). It is interesting that sarcopenia is not necessarily related to weight loss and is associated with major comorbidities including obesity. Indeed obese sarcopenic persons may have even worse health outcomes.
There are currently no estimates for the cost of sarcopenia to the NHS, but in the US functionally dependent older adults account for 50% of total elderly healthcare expenditure and the estimated health costs of sarcopenia alone amount to $18.5 billion/year.
How is sarcopenia defined and measured?
There is still no consensus on the definition of sarcopenia or in its treatment, but this is a developing area. Definitions based on loss of muscle mass alone have been difficult because, unlike bone mineral density, muscle mass measurement has not been adopted widely clinically, and muscle mass measurements alone have not consistently proved a good predictor of mortality or disability. Thus newer definitions have sought to incorporate something more than muscle mass on its own. The term ‘sarcopenia with limited mobility’ has been proposed as a better description using loss of muscle mass and low walking speed. The expert European Working Group on Sarcopenia in Older People included not only loss of muscle mass but muscle strength and function in their definition. They recommended sarcopenia should be measured in older adults aged over 65 years through low walking speed and/or poor muscle function (low grip strength/muscle mass). Incorporation of walking speed and grip strength into routine comprehensive geriatric assessment may well, therefore, be the direction forward in identifying patients who would need further diagnostic testing i.e. with bioelectrical impedance or DXA to measure muscle mass.
Nutrition and exercise are likely to be important
The interaction of age, nutrition and levels of physical activity may be highly significant in the development of sarcopenia. There is a growing body of scientific literature that suggests diet could be an important factor – and protein seems to be of particular relevance. Currently protein requirements in the UK advise similar intake in all adults regardless of age. Recently though, expert groups have suggested increasing protein recommendations for older adults. Yet paradoxically this group often consumes less protein than younger adults. Unfortunately, protein intake and efficiency of use appears to decrease with age. This may be due to a combination of factors including greater expense, increased satiety, dentition/chewing difficulties, and changes in digestion. This shortfall can promote loss of lean body mass, particularly muscle loss, increasing the older persons’ risk of such conditions as sarcopenia and osteoporosis and the falls, fractures, disabilities, loss of independence that can result. The international expert PROT-AGE Study Group concluded that protein quality, and timing of intake, may also influence the benefit from protein intake but that further studies are needed to make explicit recommendations.
Protein intake, together with activity, increases synthesis of skeletal muscle. The impact of combining physical activity and protein intake in older people may potentially have a larger impact in the prevention of muscle loss than either as an intervention on its own. However, whereas the health benefits of physical activity are undeniable, in many older populations the ability to exercise may be compromised by physical disability, frailty or disease. In such instances, appropriate physical activity should be considered, but where activity is limited, targeted control of daily protein consumption represents one of the few remaining alternatives to slow or prevent muscle loss.
Protein, protein, protein
Protein in the diet provides amino acids needed as the building blocks for the synthesis of muscle protein. Of these the branched chain amino acids, such as leucine, have been shown to have a role in boosting signals that lead to increased protein synthesis. Indeed leucine as a supplement has been proposed for prevention and treatment of sarcopenia, but results of studies of leucine supplementation have not shown consistent results. Additionally, using dietary interventions with protein-rich food has several advantages over supplementation with products such as free-form amino acids. Many plant- and animal-based protein-containing foods are readily accessible, relatively inexpensive, and palatable. For the majority of older adults the most practical means of increasing skeletal muscle protein is to include a moderate serving of protein of high biological value during each meal. Good sources of protein to include in the diet are lean cuts of meat, fish, eggs and low fat dairy products. Beans, pulses and lentils are also good choices. Often breakfast/snacks can be comparatively low in protein, so eggs and beans could be included in some breakfasts; porridge could be made with milk rather than water, and nut butters, hummus or oily fish pâté on toast can be good snack options.
Nutrition and physical activity may be the cornerstone of interventions in sarcopenia, but much of the evidence is based on short term studies and large trials are still lacking. More and larger trials will be needed to demonstrate the efficacy (and safety) of combining exercise and protein as a strategy for prevention and treatment of muscle loss. In the meantime, for the general population, the impact of a simple exercise and protein intervention, which does not require the expense of supplementation, may prove to have a useful and large impact on the wellbeing of the older person.
So whilst the clinical evidence is still lacking we should ensure that older people have adequate protein intakes and are encouraged to undertake simple physical activity if possible.
