Clinical Nutrition and Aging: Sarcopenia and Muscle Metabolism PDF

Introduction

Sarcopenia is the loss of muscle mass and strength that occurs as people age. It is difficult to know exactly how many older people experience sarcopenia, since different clinicians define it differently. According to some estimates (Sakuma and Yamaguchi, 2012), the prevalence of sarcopenia ranges from 13 percent to 24 percent in adults over sixty years of age to more than 50 percent in people eighty and older; other research (Cruz-Jentoft, 2014) indicates the international prevalence of sarcopenia is between 1 and 29 percent in community-dwelling populations, and between 14 and 33 percent in long-term care populations.

Regardless of the exact numbers, sarcopenia is a very real and common problem among older adults. It affects mobility, energy levels, and other aspects of health and well-being, and it contributes to decreased survival rates after a critical illness. In the article by Sakuma and Yamaguchi, they report that the estimated direct health-care costs attributable to sarcopenia in the United States in 2000 were $18.5 billion ($10.8 billion in men and $7.7 billion in women), which represented about 1.5 percent of total health-care expenditures for that year. For economic reasons alone, this is a serious problem

As individuals and clinicians, it is an equally serious issue. We can expect that at seventy we will not be as strong as we were at thirty. We assume that at ninety, we will be even weaker than we were at seventy. This gradual loss of muscle is perceived by most of us as “normal.” To an extent this is true—and yet not everybody gets as weak and frail. Some people retain a certain hardiness even into their eighties and nineties. Why is this so?

The implication is that there must be factors that influence the varying degrees with which different individuals experience sarcopenia. Some of these factors may be beyond our control—“good genes,” for example— but others may have to do with diet and lifestyle, factors that are in our control (at least more so than our genetic material).

Regrettably, poor diet is one of the most common problems practitioners encounter when treating older adults. Many individuals in this population have low nutrient intakes, for a variety of reasons that range from physical deficits to economic hardship. Dental problems in the elderly may make them more likely to choose softer foods that often lack protein; delayed gastric emptying can reduce appetite; hormonal changes may cause longer-lasting feelings of satiety. On top of that, meat is more expensive than foods rich in starch, and for this reason individuals who are living on a fixed income may tend to fill up on cheap, processed carbohydrates. Lack of physical strength may also make packaged, processed foods more appealing.

But these issues related to consuming poor diet are not impossible to overcome. If we can understand the lifestyle factors that influence the rate of decline in muscle mass and strength in older age, we can develop practical strategies that will help to prevent or delay sarcopenia, allowing people to maintain a higher quality of life into old age. In the first paper in this compendium, Robinson et al. consider the evidence that links diet to muscle mass and strength in the elderly. They discuss the evidence that supports the potential importance of diets of adequate quantity and quality, which the authors break down into sufficient intakes of protein, vitamin D, and antioxidant nutrients. Although much of this evidence is observational— and they are unable to describe the specific mechanisms that might help prevent or delay sarcopenia—the authors do offer us a valuable key point: sarcopenia prevention needs to begin before old age. Research confirms that the greater the peak strength attained during a person’s younger adult life, the more likely an individual will have greater strength in their older years. Early intervention can make a difference. We need to teach our students and patients that if they optimize their nutrition now, they will be investing in their future well-being.

In the second article, Vandewoude et al. look at this issue by defining two categories of sarcopenia: Primary sarcopenia, when no specific cause can be identified, is progressive and associated with the impact of aging. Changes are seen at the cellular level, with changes in motor neurons and mitochondrial function, as well at the hormonal level (resulting in insulin resistance, an increase in proinflammatory cytokines, etc.). Secondary sarcopenia is the result of both lifestyle (lack of physical activity, poor  diet) and secondary physical effects (chronic inflammation, for example). Sarcopenia, then, is both an outcome and a process. As an outcome, it is a diagnosis that causes frailty and mobility issues in older adults. As an active process, it is going on inside the body of every adult.