What makes us weaken with age? The prime culprit is sarcopenia—age-related loss of muscle mass, strength, power and function. 5%-13% of 60– to 70 year-olds and 11%-50% of people in their 80s have sarcopenia. A report predicted that the world’s over 60 population would more than triple from 2000 to 2050, with the over 80 population increasing fivefold.
While several factors play a role in sarcopenia, three major contributors will be discussed:
- reduction in muscle innervation (activation)
- oxidative damage from reactive oxygen species
- nutritional factors associated with age.
The “use-it-or-lose-it” principle explains one of the main causes of sarcopenia, a reduction in muscle innervation. The most dominant cause of sarcopenia is inactivity, both in the elderly and in the overall population. Muscle motor units-motor nerves and the muscle fibers they innervate-are codependent, implying that when the motor neurons begin to die as a result of age and/or inactivity, denervation (interruption of the nerve connection) of the muscle fibers causes atrophy (wasting away ) of the muscle cells.
As people become less active with age, they lose some of their motor neurons and face diminished function of those that remain. Importantly, muscle contractions from exercise trigger the release of muscle growth factors, including insulin growth factor and mechano-growth factor. These growth factors activate specialized cells in muscles (called satellite cells) that promote protein synthesis. Cardiovascular and resistance exercises play a major role in preventing the muscle-innervation problems that lead to sarcopenia.
Reactive oxygen species (ROS) are chemically active molecules that contain oxygen. Produced naturally by all tissues of the body during aerobic metabolism, ROS help with the cell’s homeostasis (Balance) regulation and cell messaging. Because ROS are reactive, if they are overproduced they may start attacking other molecules in cells, especially in muscle.
ROS are thought to play a key role in development of sarcopenia. That makes sense, given that skeletal muscle is the body’s largest consumer of oxygen and is vulnerable to ROS buildup. ROS can cause oxidative damage to mitochondrial proteins, cell membranes and even DNA. This damage impairs the function of ATP and protein cells from carrying out many necessary metabolic functions. Apoptosis (self-destruction of a cell) can also result from an accumulation of ROS within the mitochondria. The great news is that moderate and high-intensity exercise will promote the production of powerful antioxidant enzymes that combat the accumulation of ROS.
Diet also has an important influence on sarcopenia, with the most consistent evidence pointing to the roles of protein, vitamin D and antioxidant nutrients. The loss of appetite and hunger response as a result of aging causes an average 25% decrease in food intake between the ages of 40 and 70. This decrease in nutrient consumption leads to insufficient protein intake and low micronutrients levels.
Many vitamins and minerals play key roles in health muscular and neutral function. There is a significant increase in the likelihood of frailty in elderly populations with low vitamin D status, thus implicating the association with vitamin D insufficiency and sarcopenia.
It is clear that sarcopenia is a prevalent and debilitating disorder with several causes, effects and counteractions. Moderate-and-high-intensity cardiovascular exercise and resistance training can counteract neural decay and produce the antioxidants needed to fight the reactive oxygen species. An exercise program coupled with a proper nutritional plan provides a meaningful strategy that can make the difference between debilitation and a healthy, active lifestyle.