The pandemic associated with infection by the SARS-CoV-2 virus, which causes Covid-19 syndrome in its various manifestations, has stimulated reflection and deepening about therapies, habits, and routines as the best way to fight the disease. Different studies suggest obesity as one of the main risk factors for severe forms of Covid-19, increasing the chances of a poor prognosis. Consequently, the question about the possible protective role of physical exercise and physical fitness indirectly favoring a balanced immune response emerged as one of the hypotheses related to possible good prognoses in this disease.
Also, read ESC 2020: Exercise guidelines for patients with cardiovascular disease.
Covid-19 immune response
Immunity during the infectious process by SARS-CoV-2 depends on genetic factors (HLA genes), age, sex, nutritional and physical status, and associated risk factors such as smoking, obesity, type 2 diabetes, and metabolic syndrome. These last three factors lead to greater expression of ACE2 receptors (used in the entry of SARS-CoV-2) in tissues such as adipose, pro-inflammatory state, and hypercoagulability.
The initial effective immune response to intracellular agents, such as viruses, involves the production of type I interferon (INF-I), which directs macrophagic and lymphocyte action to eliminate the viral spread. In Covid-19, suppression of the IFN-I response is observed, with consequent dysfunction of the initial mechanisms of infection control, hyperinflammatory infiltrates composed of neutrophils, macrophages, and monocytes in lung tissue and a period of cytokine storm(storm of pro-inflammatory cytokines) with lymphopenia, as well as changes in coagulation and circulatory factors, and viral spread. This process results in injury to lung tissue infected with SARS-CoV-2 (or others subjected to indirect immune attack by deregulation of the immune system). It culminates in the acute respiratory distress syndrome with evolution to the need for oxygen therapy, to possible shock septic, multiple organ failure, and death.
Exercises as prevention
The regular practice of physical exercise acts as a modulator of the immune system to progressively structure the physiological response to minimize damage. During physical activity, a series of pro and anti-inflammatory cytokines are released, there is an increase in lymphocyte circulation and cell recruitment. Such effects lead to better control of the inflammatory response, reduced stress hormones, and lower incidence, intensity of symptoms, and mortality in the face of viral infections, especially respiratory ones.
Different studies suggest that regular exercise reduces pneumonia, including influenza mortality, and favors cardiorespiratory functions, vaccine response, glucose, lipid, and insulin metabolism. Researchers suggest that the practice of physical exercise, both acutely and chronically, has a significant benefit in modulating systemic inflammation, in addition to contributing to body weight control. It is known that the best modulatory effect is related to greater regularity, intensity, type, and duration of effort over time.
It is also known that moderate-intensity physical exercises, performed ≥ 3 times a week lasting 45-60 minutes and 50-70% of the maximum oxygen consumption, stimulate cellular immunity by increasing the release of IL -2, Natural killer cell recruitment(NK), reduced oxidative stress, increased leukocyte concentration (30-120 min after physical activity persisting for up to 24 hours), and IFN-γ stimulation and suppression of IL-1β, IL-6, and TNF-α, providing better immune vigilance. Dynamic exercises with a greater cardiorespiratory attribute promote the mobilization and redistribution of effector lymphocytes, mediated by catecholamines. Muscle contraction, by itself, is responsible for the transient increase in IL-6 levels in proportion to the duration of physical activity and the amount of muscle mass recruited. The increase in the levels of this cytokine appears to increase the levels of anti-inflammatory cytokines, such as IL-10, released by innate immunity cells. IL-10 is also associated with increased insulin sensitivity and glycemic metabolism.
Learn more: Exercise during the coronavirus pandemic
The practice of physical exercise leads to a reduction in the concentration of pro-inflammatory adipokine and increases sensitivity to leptin and insulin. However, there are controversies regarding the physical practices of prolonged (> 2 hours and> 80% of the maximum oxygen consumption) or high intensity (especially in an unusual way) without adequate rest, with impairment of cellular immunity, with a possible greater propensity to infectious diseases due to reduced expression of Toll-like receptors (TLR) with consequent suppression of the response via T helper type 1 (Th1), reduced neutrophil chemotaxis, reduced immunoglobulin production, the release of IL-4 and IL-10, and to the increase in TGF-β.
Compared to Covid-19, there are still limited data on how physical exercise can help immune response to the new coronavirus. However, it is observed, for example, that diabetic patients with adequate glycemic control and infected with SARS-CoV-2 have a better prognosis in Covid-19. It is also suggested that the anti-inflammatory, antioxidant, and inhibition of endothelial activation benefits provided by physical activity are linked to the reduction of hypercoagulability associated with this disease.
It is noteworthy that some of the measures needed during the lockdowninstituted in many countries were the closing of clubs, gyms, and sports practice studios. Consequently, it is a fact that social isolation has led to changes in behavior and psychological and physiological changes, including an increased prevalence of anxiety, depression, alcoholism, smoking, sedentary lifestyle, and eating disorders such as hyperphagia and binge eating. Such changes resulted in negative consequences for the general population, with possible long-term problems for Public Health, such as weight gain, increase in adipose tissue, hyperglycemia, insulin resistance, and loss of muscle tissue. Additionally, this context favors greater susceptibility to stressful events and elevation of glucocorticoids (cortisol), with consequent inhibition of the functions of NK cells and CD8+ T lymphocytes.
Therefore, moderate and regular physical exercise should be especially encouraged during confinement as a measure for the prevention of metabolic, physical, and psychological diseases. The World Health Organization (WHO) recommends that healthy asymptomatic individuals practice moderate-intensity physical exercise for at least 150 minutes a week (adults) or 300 minutes a week for children and adolescents, distributed 3-4 times a week. Such practices should include aerobic and strength exercises, indoors or outdoors, following local government regulations. And advises that physical activity should be interrupted at the onset of any symptoms such as fever, dyspnea, and dry cough.
Additional aspects of physical exercise and Covid-19 are described in the references below.