Nutritional risk refers to the risk of adverse clinical outcomes from existing or potential nutritional and metabolic conditions[18]. COVID-19 is a highly contagious disease. Severe cases are often combined with other organ dysfunctions and are prone to malnutrition[19]. Nutritional status is crucial to the maintenance of the body's immune function. Malnutrition not only impairs immune defense mechanisms, but may also increase susceptibility to infection[20]. In addition, malnutrition can also be the result of infection. Thus, reasonable nutritional support can timely prevent the increase in the incidence of multiple organ failure, improve the patient's immune function, shorten the course of disease, and reduce the mortality rate[5]. Nutritional risk screening is the first step in nutritional support. Studies have demonstrated that NRS2002 has higher sensitivity than other traditional nutritional screening tools[21]. In this study we found 7.9% of COVID-19 patients with nutritional risk. Previous studies have shown that 82.6%-92% of patients with COVID-19 are with nutritional risk[22–24]. In the literature, 9.96% of COVID-19 patients at nutritional risk was closest to our findings[25]. The inconsistency may be due to the fact that most of the patients in this study were non-critical, while only 44 were critical, and the median age was only 37 years, with a predominance of young people in the onset population and a larger sample size. Old age has been shown to be an important risk factor for deterioration and death in patients with COVID-19[26, 27]. Patients with more severe disease are more likely to be at nutritional risk[28].
In previous studies with a median age of 60 years, patients with COVID-19 at nutritional risk were older than those without nutritional risk[22]. Because elderly patients are more prone to reduce nutrient absorption due to symptoms such as loss of appetite and decreased intestinal function, combined with the combination of COVID-19, inadequate intake due to stress and fear[29], compensatory effects of hypoxia on vital organs, and gastrointestinal reactions such as nausea, vomiting, and anorexia caused by some medications during treatment, making these patients more susceptible to nutritional risk[30]. And patients with COVID-19 who are at nutritional risk are more likely to develop complications and have longer hospital stays[31]. In contrast, our findings are inconsistent with this, COVID-19 patients with nutritional risk were younger and duration of hospitalization longer than those without nutritional risk, but the differences were not statistically significant. The reason may be related to the median age of 37 years in our study, which was predominantly young, and the low proportion of patients with nutritional risk, which was only 7.90%.
Meanwhile, we found that COVID-19 patients with nutritional risk had a longer time to coronavirus negative than those without nutritional risk. Nutrition plays a key role in improving immunity. For viral infectious diseases, nutritional status affects the viral genome mutation from benign or minimally pathogenic viruses to highly pathogenic viruses and their transmission in the host[32]. If there is a nutritional risk, it can directly affect the immune defense.
ALB, TP and HGB are commonly used in clinical practice as indicators of malnutrition. Studies have suggested ALB and HGB have a negative correlation with NRS2002 score[33]. This study showed that ALB level, HGB level, and TP level were significantly lower in patients with nutritional risk than those without nutritional risk, and that ALB level was a significant factor on disease severity. This finding is consistent with the literature conclusions[28, 34] that ALB is a reliable indicator of nutritional status and correlates with the prognosis of the severity of COVID-19[35]. Low ALB level indicates nutritional deficiencies or an organism in a state of intense stress[36]. We speculate that the lower ALB in COVID-19 patients with nutritional risk may be due to reduced protein synthesis and increased consumption due to poor appetite, stressful conditions, and more comorbidities in patients.
In addition, this study found that in with-nutritional risk group the proportion with three or more comorbidities was significantly larger, the rate of critical illness and mortality were higher than those without-nutritional risk group. Similarly, nutritional risk has an important influence on disease progression and prognosis in patients with COVID-19. The more patients have comorbidities and the more serious their conditions are, the more likely they are to have impairment of organ function[37], and coupled with the fact that patients are severely underfed or unable to eat, have disrupted catabolism, or even have viruses directly invading the digestive system to impede nutrient absorption[38], they are more prone to malnutrition and have a greatly increased probability of nutritional risk. This results in further impairment of the patient's immune function and contributes to the progression from asymptomatic infection, light, and common to severe and critical forms, thus causing a poor prognosis.
Previous studies have shown that the NRS2002 score can be an appropriate and practical predictor of prognosis for COVID-19 patients[23, 39], an independent predictor of the clinical type of COVID-19 patients[25], and indirectly reflecting the severity and prognosis of COVID-19[40]. In this study, the NRS2002 score not only had a significant impact on disease progression and prognosis in COVID-19 patients, but also had a good predictive value for both disease severity and prognosis, with cutoff value of 0.5, 5.5, respectively. The higher the NRS2002 score, the greater the risk of critical illness and the worse the prognosis of COVID-19 patients. Therefore, early screening for nutritional risk in patients with COVID-19 is crucial. Reasonable nutritional support is extremely important for patients with severe COVID-19. Infections can be better controlled with nutritional support, improving the patient's prognosis.
However, there are still some limitations of this study. Importantly, it was a single-center, retrospective study, and all the inherent limitations of retrospective studies are unavoidable and do not allow for causal inference. And the number of severe cases, especially deaths, was small. Moreover, we did not systematically collect data on patient-specific dietary intake, malnutrition diagnosis and nutritional support. We realized that this information may be useful from a clinical point of view in the management of patients with COVID-19.