Sarcopenia, a condition that causes loss of muscle mass, is a common ailment that comes with aging. It wouldn’t be correct to talk about who is affected and who isn’t, because everyone experiences at least some degree of muscle mass loss, along with reduced strength, after age 40 or 50. As you may imagine, sarcopenia’s greatest impact is among sedentary people who exercise rarely if ever, but even high-performing athletes eventually experience progressive loss of muscle mass.
The most widely accepted explanation as to why sarcopenia happens is that it is a consequence of inflammaging—a chronic, low-grade inflammatory status.
Inflammaging at a glance
In simple terms, inflammation is a biological response to the presence of harmful stimuli, such as pathogens or damaged cells, in body tissues. As such, inflammation is supposed to last only as long as necessary to eliminate the original threat and then disappear; this type of inflammation is known as acute inflammation. By contrast, chronic inflammation drags on beyond what’s good for you, leading to damage to your tissues and potentially to a number of diseases, such as rheumatoid arthritis or even cancer.
As we age, we tend to develop a sort of background inflammation process termed inflammaging that, albeit low-grade, constantly goes on and increases over time. Cellular senescence, among others, is one of the inflammatory sources contributing to this process.
Inflammaging and muscle mass loss
Inflammaging is thus characterized by the presence of inflammation biomarkers in the blood. One of these markers is the C-reactive protein (CRP). Elevated levels of CRP are typical of many illnesses and of inflammaging as well. A recent study published in the journal Cellular Physiology and Biochemistry set out to establish a causal link between CRP and loss of muscle mass—a link that, up to this point, had only been correlational.
The study was in two parts. First, the researchers assessed muscle mass and CRP blood levels in a cohort of 118 elderly women, determining the correlation between the two values. The results showed that, in elderly subjects with low muscle mass, C-reactive protein levels were significantly higher than in subjects of the cohort with normal muscle mass, and vice versa.
Secondly, the researchers wanted to establish how CRP actually affects muscle cells. To do so, they used an in vitro culture of human muscle cells exposed to CRP. They observed that exposure of muscle cells to CRP affects their protein synthesis. Since muscle cells normally contain very high levels of proteins, this interference leads to a reduction in the size of muscle cells and thus of muscle mass in general.
While a dietary supplement called HMB has shown some efficacy in preventing the loss of muscle mass in patients affected by sarcopenia, there is no approved medical treatment for it. Exercise provides some benefits, while the lack thereof appears to be a significant risk factor.
This study explains how chronically elevated CRP levels may contribute to age-related muscle mass loss, and this is, of course, of interest when developing potential therapeutic approaches against sarcopenia; a better understanding of its underlying mechanisms may one day allow us to interfere with them and maintain muscle tone and vigor well into old age.
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