TNF and COVID-19: A high CRF has also been reported to positively impact the expression of immune markers that could theoretically reduce the risk of COVID-19 complications [40], particularly the so-called cytokine storm syndrome [40]; that is, the excessive, uncontrolled release of proinflammatory cytokines (e.g., interferon-γ, IL-1, IL-6, IL-18, tumor necrosis factor [TNF]-α) to the bloodstream that is frequently found in patients with severe disease, including COVID-19 [41].