Muscle, or lean body mass (LBM) can be lost at any age as the result of
injury, disease, emotional stress, diet, malnutrition and any other number of
factors.
Despite the cause, muscle loss is clinically significant because it erodes
strength, endurance, health and vitality. In contrast to LBM loss resulting from
individual adverse circumstances, sarcopenia is a condition characterized by
muscle atrophy that affects everyone as the result of aging. Surprisingly,
muscle loss begins early in life; upon completion of development and as early as
twenty or twenty-five years of age. This indicator of aging onset is clearly
evident as loss of speed, strength and endurance in middle-aged athletes, which
is presumably less than in non-athletes. Clinical studies have shown that the
excretion of urinary creatinine, which is a measure of muscle creatine content
and total muscle mass, decreases by nearly 50% between the ages of 20 and 70
years. These measurements indicate that degradation of muscle exceeds its
synthesis soon after young adulthood is past and suggests that senescence begins
much earlier in life than is generally presumed. Thus, interventions in aging
focused upon sarcopenia may have great value for increasing duration of life and
improving its quality.
A large component of involuntary weight loss during aging occurs in fat-free
mass. By age thirty, body weight gain begins to be preferentially accrued as fat
instead of muscle and this process that underlies loss of LBM continues unabated
thereafter. However, the lost muscle is usually not noticed by affected
individuals, because it is replaced in subtle ways such as by padding areas of
loss with extra fat. After forty years of age, muscle loss proceeds at a rate of
0.5 - 2% per year or about 8% per decade on average. This rate accelerates
noticeably after age 60 and is highest in physically inactive persons along with
a parallel decline in dynamic, static, and isokinetic muscle strength. The
result of such age-related LBM loss is a decline in function such that up to 65%
of older men and women report that they are unable to lift ten pounds with their
arms. From age 60 and for each decade thereafter, the rate of muscle loss
doubles.
Since maintaining muscle mass is essential to supporting whole-body protein
metabolism, wound healing, physical strength, organ function, skin integrity and
immune function, sarcopenia can be debilitating. Consequences of age-related
muscle loss include:
- frailty—reduced ability to walk, climb stairs, rise from a chair, and carry
a load
- physical disability—3- to 4-fold greater risk, independent of age, gender,
obesity, ethnicity, socioeconomic status, chronic morbidity, and health
behaviors
- loss of independence—reduced ability to cope with major illness and limited
capacity to participate in activities due to diminished aerobic capacity
- depression—due to loss of independence
- increased mortality
Health care costs of people with sarcopenia accelerate as they become
increasingly disabled. In the United States in 2000, the estimated direct health
care costs related to sarcopenia totaled $18.5 billion or about 1.5% of the
total health care expenditures for that year. Excess annual health care
expenditures were $860 and $933 for every man and woman with sarcopenia,
respectively. In fact, a 10% reduction in the prevalence of sarcopenia would
save $1.1 billion a year in US health care costs.
Since reduced skeletal muscle mass during aging is an important and basic
cause of morbidity that is significantly and independently associated with
functional impairment and disability, the challenge to longevity medical
practitioners is to develop effective and practical interventions to prevent or
at least partially reverse sarcopenia. Such effort may succeed in identifying
beneficial changes in life style, exercise regimens, and novel pharmacological
or nutritional therapies to protect us all against this particularly malignant
scourge of aging.
Dr. Richard Walker, Editor-in-Chief
Clinical Interventions in Aging
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