The interest in verifying the occurrence of sarcopenia and cachexia in the population with COVID-19 is not only due to a better understanding of the nutritional impairment promoted by the disease, but also to verify the prognostic impact of these previous nutritional conditions on the evolution of the disease. It is already well established that the occurrence of sarcopenia and cachexia is associated with higher morbidity and adverse outcomes [9, 10].
To the best of our knowledge, this is the first case-control study to investigate the association between the occurrence of sarcopenia and cachexia with prognostic markers in hospitalized patients with COVID-19. The prevalence of sarcopenia among COVID-19 inpatients found in our study was similar to that reported in a retrospective cohort study by Kim et al. (2021) [23] (prevalence of 23.97%) and a study by Moctezuma-Velazquez et al. (2021) [13] (prevalence of 22.16%).
There is growing evidence suggesting that SARS-CoV-2 infection can result in gastrointestinal abnormalities, which can lead to inadequate nutritional intake. In addition, the infection can also cause body composition abnormalities by recruiting inflammatory cytokines, such as IFN-γ, IL-1β, IL-6, IL-17, and TNF-α, which can cause pathological changes in skeletal muscle tissue. The virus can directly bind to muscle tissue through the angiotensin 2 receptor (AT2 receptor), leading to muscle fiber proteolysis and inhibition of protein synthesis, which can lead to the development of sarcopenia and cachexia [24, 25].
Underweight was present in 6.5% of the COVID-19 patients, indicating that sarcopenia occurred independently of changes in weight. It is important to highlight that the occurrence of sarcopenia is associated with a higher risk of adverse outcomes, such as susceptibility to infections, rehabilitation needs, longer hospitalization, and mortality. Therefore, the occurrence of sarcopenia should be evaluated in hospitalized patients, especially in acute conditions such as COVID-19 [8, 9, 10].
Regarding cachexia, few studies have evaluated this condition in patients with COVID-19. So far, only two studies have investigated the diagnosis of cachexia during the hospitalization of these patients, and both focused on patients admitted to the Intensive Care Unit (ICU) or semi-intensive care unit. Allard et al. (2020) [26] reported a prevalence of 37.04%, while Pironi et al. (2021) [27] described a prevalence of 24.25%.
Our findings indicated a cachexia prevalence of 28.1% in the COVID-19 group. This is concerning data, as cachexia is a complex metabolic condition that is not only associated with underlying disease but can also result from worsening malnutrition and/or sarcopenia [28]. Cachexia further increases the risk of disability and mortality, and individuals who survive the cachexia condition often require longer rehabilitation [29, 30].
The lack of differences in the prevalence of sarcopenia and cachexia between COVID-19 patients and controls in our study does not necessarily imply that COVID-19 does not increase the risk for these conditions. It is important to note that our study protocol involved an evaluation for sarcopenia and cachexia within 72 hours of hospital admission, and thus, we were unable to evaluate the effects of the progression of SARS-CoV-2 infection on nutritional parameters.
In addition, it is important to highlight the changes in the epidemiological scenario of COVID-19 worldwide after expanding vaccine coverage. At the time the study was developed, there was already vaccination coverage with up to 2 doses, which may have contributed to less muscle stress caused by the viral infection. In accordance, some studies have already evaluated the nutritional status of patients with COVID-19, based on serum markers, such as Retinol Binding Protein (RBP) in the period before and after vaccination. These studies saw that individuals after vaccination maintained RBP at higher levels, reflecting that vaccination would be able to reduce comorbidities and protein-muscle impairment [31].
In our study, TLC was higher in the COVID-19 group compared to the control group. This can be attributed to the inflammatory-infectious condition observed in COVID-19 patients, and thus, this result was expected. While TLC is often used as a nutritional parameter, its interpretation should be approached with caution in the presence of infection and inflammation.
The higher mean age in individuals with sarcopenia is an expected finding, supported by evidence showing an association between older age and lower BMI in this population [14]. Aging itself increases the risk of sarcopenia due to the decline in muscle mass and strength caused by changes in muscle cellular metabolism. These changes promote alterations in the structure of muscle fibers, neurodegeneration, a decrease in the number of motor muscle cells, impairment of protein anabolism, hormonal resistance, and when coupled with physical inactivity and inadequate nutritional intake, ultimately lead to sarcopenia [32]. The higher mean age in individuals with sarcopenia is an expected finding, supported by evidence showing an association between older age and lower BMI in this population [14]. Aging itself increases the risk of sarcopenia due to the decline in muscle mass and strength caused by changes in muscle cellular metabolism. These changes promote alterations in the structure of muscle fibers, neurodegeneration, a decrease in the number of motor muscle cells, impairment of protein anabolism, hormonal resistance, and when coupled with physical inactivity and inadequate nutritional intake, ultimately lead to sarcopenia [32].
The lowest PA values observed in patients with sarcopenia in our study are consistent with previous findings that show lower PA levels in sarcopenic individuals and a higher prevalence of sarcopenia in those with lower PA [33, 34]. PA has been demonstrated to be a useful risk marker for sarcopenia [35, 36], as well as having prognostic value for adverse outcomes [37, 38].
Similar results were observed in patients with COVID-19. PA values were found to be independently and inversely correlated with adverse outcomes in COVID-19, including the risk of ICU admission, complications, length of hospital stay, and mortality [39, 40, 41]. Some evidence suggests that PA is associated with sarcopenia, as it may reflect water distribution, body muscle cellularity, and muscle strength, which are components used in the definition of sarcopenia [34].
The higher 4C Mortality Score observed in sarcopenic patients in the COVID-19 group suggests a greater risk among these patients. This finding supports the hypothesis that muscle-protein depletion may lead to worse outcomes in individuals with COVID-19. In a recent meta-analysis, individuals hospitalized with COVID-19 who had prior nutritional impairment had a 10-fold higher risk of mortality compared to those without impairment [42]. However, it is important to consider the higher mean age of sarcopenic individuals in this study, as it may be a confounding variable in the analysis of this association.
The lowest BMI and highest percentage of weight loss observed in patients with cachexia are expected findings, as these two aspects are included in the diagnostic criteria for this condition and are consistent and well-predicted in scientific evidence [11, 43, 44].
Since the onset of the current pandemic, several scientific studies have aimed to identify clinical and laboratory predictors of poor prognosis that can assist healthcare teams in monitoring strategies and making therapeutic decisions.
All patients included in our study had received at least one dose of the COVID-19 vaccine at the time of data collection. However, nearly 80% of the sample did not have a complete vaccination schedule, which may pose an additional risk for severe COVID-19 progression. The lack of a complete vaccination schedule may be associated with a greater inflammatory profile and, consequently, a higher risk of sarcopenia (muscle-protein depletion). To the best of our knowledge, this is the first study to investigate the association between COVID-19 vaccine doses and the occurrence of sarcopenia and cachexia.
NLR is an inflammatory biomarker that can be used as an indicator of systemic inflammation [45]. It has been extensively investigated as a possible prognostic factor in the progression of COVID-19. NLR at the time of hospital admission can predict mortality and ICU admission in COVID-19 patients [21]. The association of NLR with cachexia may suggest that cachexia is linked to a worse inflammatory profile and a higher risk of developing negative outcomes. However, our study did not find significant values for this association.
Our study had some limitations. The sample size was relatively small, which may limit the generalizability of the results. Additionally, the evaluation of sarcopenia and other nutritional measurements was conducted up to 72 hours after hospitalization, which may restrict the observation of the effects of COVID-19 evolution on nutritional status. Nevertheless, the inclusion of a control group for comparative purposes was a strong point of our investigation.