Sarcopenia is a disease associated with the aging process. Loss of muscle mass and strength, which in turn affects balance, gait and overall ability to perform tasks of daily living, are hallmark signs of this disease. Most people begin to lose modest amounts of muscle mass after age 30, but the resulting loss of strength increases exponentially with age.
Possible effects of sarcopenia include decreased muscle strength, problems with mobility, frailty, weak bones (osteoporosis), falls and fractures, decreased activity levels, diabetes, middle‐age weight gain and a loss of physical function and independence.
Stages of Sarcopenia
Different stages of sarcopenia may be used to help identify the severity of the condition, such as:
- Pre-sarcopenia: Characterized by reduced muscle mass. No reduction in muscle strength or physical performance
- Sarcopenia: Characterized by the presence of low muscle mass and low muscle function (strength OR performance)
- Severe sarcopenia: Characterized by reduced muscle mass and reduction in muscle strength.
Pathophysiology of Sarcopenia
Immobility and malnutrition, especially low protein intake, could deteriorate sarcopenia, and the influence of multiple factors leading to aging-related sarcopenia. Skeletal muscle consists of two types of fibers: Type I and Type II. Type II fast fibers have a higher glycolytic potential, lower oxidative capacity, and faster response as compared to type I slow fibers. Type I fibers are known as fatigue-resistant fibers due to their characteristics that include greater density of mitochondria, capillaries and myoglobin content. With age, atrophy almost only affects type II fibers. Molecular mechanisms of sarcopenia are not fully understood. Some factors have been suggested to be involved as described below.
Changes in Hormones and Metabolism: GH is released from the pituitary gland and promotes IGF-1 secretion. IGF-1 binds to the IGF-1 receptor and activates its downstream Akt/ mammalian target of rapamycin (mTOR) pathway. mTOR induces muscle hypertrophy by promoting protein synthesis. Akt inhibits FOXO transcriptional factors and blocks the upregulation of E3 ubiquitin ligases, or muscle RING-finger protein-1 (MuRF1) and Muscle Atrophy F-Box (MAFbx), which stimulate protein degradation. Therefore, the decrease of GH and IGF-1 might be involved in sarcopenia. Insulin is also an anabolic hormone and activates Akt/mTOR pathway. Skeletal muscle protein synthesis is resistant to the anabolic action of insulin in older subjects, and this could be involved in the development of sarcopenia.
Neuromuscular Aging: Neuron loss is a progressive, irreversible process that increases with age. Multiple levels of the nervous system are affected by age, including the motor cortex, the spinal cord, peripheral neurons, and the neuromuscular junction. As age goes these leads to degeneration and could be the cause of sarcopenia.
Systemic Inflammation: As humans age, the serum level of tumor necrosis factor-a (TNF-α), interleukin-6 (IL-6), interleukin-1 (IL-1) and C-reactive protein (CRP) elevate. Adipose tissues are supposed to secrete these cytokines. A theory called inflamm-aging (inflammation +aging) proposes that, as humans age, systemic low-grade inflammation is one of the causes of various diseases such as atherosclerosis, dementia, type 2 diabetes, and osteoporosis. The high-sensitivity CRP levels are significantly and independently associated with sarcopenic obesity. Inflamm-aging might be involved in sarcopenia.
Causes and Risk factors
A common cause of sarcopenia is decreased physical activity throughout the day. However, although less frequent, some people with active lifestyles may also be diagnosed with sarcopenia. This suggests that there could be other reasons for the development of the disease.
Researchers currently believe that other causes of sarcopenia could include:
- A reduction in the nerve cells that send signals from your brain to tell your muscles to move
- A lowering of your hormone levels
- A decline in your body’s ability to convert protein to energy
- Not consuming enough daily calories and protein in order to maintain your muscle mass
Symptoms of Sarcopenia
Symptoms of sarcopenia may vary depending on how much muscle mass a person has lost. Symptoms include:
- A decrease in muscle size
- Loss of endurance
- Poor balance
- Trouble climbing stairs
A decline in muscle mass may not seem like a big concern for most people. However, muscle loss can be significant enough to cause weakness, increase fall risk, and limit a person’s independence.
Sarcopenia may also cause a person to reduce their participation in physical activities. This decrease in activity causes even further muscle loss, which can adversely affect a person’s quality of life.
Complications of Sarcopenia
Sarcopenia has been linked to metabolic problems like type 2 diabetes, high blood pressure, and obesity. These conditions put you at greater risk of developing coronary heart disease, stroke, and other conditions that affect the blood vessels.
Sarcopenia has a pervasive, negative impact on patients’ quality of life and often leads to:
- Increased inpatient length of stay
- A decline in daily activities and ambulatory function
- Reduced day-to-day activities
- Increased risk of illness and infection
- Reduced recovery from surgery, illness, and injury
- Poor wound healing
- Increased mortality
Diagnosis and Test
Sarcopenia should be diagnosed in three criteria:
i) Muscle mass:
- Computed Tomography scan (CT scan).
- Magnetic Resonance Imagery (MRI).
- Dual Energy X-ray Absorptiometry (DXA).
- Bioimpedance analysis (BIA).
ii) Muscle strength:
- Handgrip strength.
iii) Physical performance:
- Short Physical Performance Battery (SPPB).
- Gait speed.
- Grip strength.
- Thigh muscle thickness ratio.
Treatment and Medications
Hormone replacement therapy (HRT)
HRT can help to raise lean body mass, decrease abdominal fat, and prevent bone deterioration in women whose hormone levels decrease with menopause. However, the use of HRT is debated because of an increased risk of some cancers and other severe health conditions.
- Some other treatments that are under investigation include:
- Growth hormone supplements
- Testosterone supplements
- hydroxymethyl butyrate
- Angiotensin-converting enzyme inhibitors
- Vitamin D
- Medications for the treatment of metabolic syndromes
Although drug therapy is not the preferred treatment for sarcopenia, a few medications are under investigation. They include:
Urocortin II. This has been shown to stimulate the release of a hormone called adrenocorticotropic hormone (ACTH) from your pituitary gland. Given through an IV, this can prevent muscle atrophy that can happen when you’re in a cast or taking certain medicines. Its use for building muscle mass in humans has not been studied and isn’t recommended.
Other treatments under investigation for sarcopenia include:
- Testosterone supplements
- Growth hormone supplements
- Medication for the treatment of metabolic syndrome includes insulin resistance, obesity, and hypertension).
Instead of medication or hormone therapy, management of sarcopenia focuses on lifestyle changes to prevent muscle loss. These usually include:
Strength training or resistance training can improve muscle size, strength, and tone. It can also strengthen bones, ligaments, and tendons, which is good for a person’s overall health. Strength training involves using resistance to cause muscle contraction. The muscle contraction builds muscle size and increases strength. Strength training may involve using weights, resistance bands, or exercise machines. A person’s own body weight can also be used for resistance.
Proper nutrition is essential to treat sarcopenia, and may even prevent or delay the condition. Healthy protein. Healthy sources of protein, such as fish, nuts, lentils, and quinoa, can help to build up and sustain normal muscle mass levels.
Eating enough protein is an important dietary consideration in preventing sarcopenia. The IOF recommend that adults eat 1.0-1.2 grams of protein per kilogram of body weight daily.
Taking certain dietary supplements may be another way to improve sarcopenia or help prevent the condition. For example, taking creatine supplements may increase strength and lean muscle mass in adults of any age. Similarly, maintaining adequate levels of vitamin D, either through diet or supplements, may help older adults maintain muscle strength.
Prevention of Sarcopenia
Lack of activity is the most common reason behind this condition. Therefore, being physically active may lessen your chances of getting sarcopenia. Just half an hour of moderate exercise each day, like walking or jogging, will help keep your system working and fit.
In order for exercise to be effective, proper nutrition is also important. Research has shown that consuming more protein may help older adults reduce their chance of sarcopenia. Supplements have also proven useful in the prevention of sarcopenia. Some include:
- Creatine, for increasing and maintaining muscle mass
- Vitamin D, for maintaining bone and muscle tissues
- Whey protein, to help preserve body mass