Functional centenarians represent an impressive example of successful healthy ageing. Ageing is a continuum of biological processes, characterized by progressive adaptations heavily influenced by genetic and physiological factors. However, even in these truly unique individuals, declining lung function and sarcopenia (loss of muscle) lead to a progressive fall in strength and reduced exercise capacity. The subsequent limitation in mobility can initiate a vicious decline in physical function and health. Recent studies have shed some light on this multi-factorial decline in function associated with aging and the positive role that diet and exercise play in the elderly. This loss of muscle called sarcopenia is very important in maintaining independence and function in centenarians.
The more muscle older adults maintain, the lower their risk of death. People with the highest levels of muscle mass are less likely to die than those with the lowest levels of muscle mass. Similarly, people with the higher levels of cholesterol are also less likely to die. Low muscle mass and strength are independently and significantly associated with an increase of all-cause mortality among U.S. older adults regardless of muscle mass, metabolic syndrome risk factors, sedentary time, or leisure time physical activity. Rather than worrying about weight or body mass index, we should be focusing more on maintaining muscle mass.
We all have elderly relatives who have obvious cognitive deficits such as speech and memory problems. An underappreciated fact is that less than 20% of centenarians are truly physically independent. Moreover, age-related cognitive dysfunction plays a significant role in centenarians, many studies show that less than 10% of centenarians display completely preserved cognitive function.
Lack of exercise is a major risk factor for sarcopenia. Muscle fiber numbers begin to decrease around 40-50 years of age. The decline in muscle fiber and strength is more pronounced in patients with sedentary lifestyles as compared to patients who work out. Even professional athletes such as marathon runners and weight lifters show a gradual, albeit slower decline in their speed and strength with aging.
HORMONES AND INFLAMMATION
Age-related decreases in hormone concentrations, including growth hormone, testosterone, thyroid hormone and insulin-like growth factor, lead to a loss of muscle mass and strength. Extreme muscle loss often results from a combination of diminishing hormonal anabolic signals and inflammation. Promotion of inflammatory cytokines such as tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL-6) affect muscle physiology. Some studies suggest that if you naturally produce a lot of IL-6 (due to genetics) you may lose muscle faster than others.
PROTEIN SYNTHESIS AND REGENERATION
A decrease in the body’s ability to synthesize protein, coupled with inadequate intake of calories and/or quality protein to sustain muscle mass, is common in sarcopenia. Oxidized muscle proteins increase with aging and lead to a buildup of what are called cross-linked proteins. These proteins are not easily removed (via the proteolysis system). This leads to an accumulation of non-contractile, dysfunctional protein in skeletal muscles, and is part of the reason muscle strength decreases in sarcopenia. This model may change as the body becomes less insulin resistant and optimized fat adaptation takes placed.
Evolutionary theories implicate sedentary behavior and the failure of the human body to maintain muscle mass and function with aging. This hypothesis suggests that genes suited for high levels of obligatory muscular effort, i.e. running from the tiger, were required for survival in the Late Paleolithic era. Our modern lifestyle is characterized by high levels of lifelong sedentary behavior. Basically, a fancy way of saying use or lose it.
EARLY DEVELOPMENTAL INFLUENCES
Epidemiological research into the developmental origins of health and disease has shown that early environmental influences on growth and development may have long-term consequences for human health. For example, low birth weight, a marker of a poor early environment, is associated with reduced muscle mass and strength later in life.
OBESITY and SARCOPENIA
Sarcopenic Obesity is a medical condition in which low lean body mass seen in sarcopenia is combined with high fat mass. It is associated with impaired functional capacity, disability, metabolic complications and increased mortality. Low muscle mass along with high fat mass is also characteristic of the aging process. Likewise, we know that obesity greatly increases the chance of death. Many studies that investigate how obesity and weight affect the risk of death look only at BMI. But it should be noted there is no gold-standard measure of body composition, several studies have addressed this question using different measurement techniques and have obtained different results.
It has long been thought that the age-related loss of weight, along with a loss of muscle mass, was largely responsible for muscle weakness in older people. However, studies in patients with Sarcopenic Obesity reveal that changes in muscle composition are also important. ‘Marbling’, or fat infiltration into muscle, lowers muscle quality and work performance. It must be remembered that marbling occurs with an over consumption of carbohydrates, usually grains.