Exercise and Immune Function in the world of COVID-19
During my now virtual clinic visits, many of my patients report a long lapse in physical activity due to the restrictions imposed by the COVID-19 pandemic. They cite closed gyms and parks, social distancing stipulations, and upended schedules and routines as culprits for their inactivity. As a fitness junkie, this saddens me. But as a physician, it deeply concerns me. Exercise is powerful medicine. Arguably, we need frequent dosing now more than ever.
When SARS-CoV-2 (the virus that causes COVID-19) invades the human body, our immune recognizes it as foreign and attacks. This clash between invader and protector generates chemicals called cytokines that work in concert with white blood cells, T-cells, NK cells, and others to fight infection. Inflammation manifests as redness, pain, heat, and swelling. It is not the virus itself, but rather this acute inflammatory response that damages lung tissue and necessitates extreme medical interventions such as mechanical ventilation.
Physical activity is a critical component of the prevention strategy for COVID-19 and other infectious diseases thanks to its immune boosting, inflammation modulating, and stress reducing effects.
A bout of exercise boosts immune function by its direct effects on cells and molecules in the blood. A recent study confirmed that a single session of exercise alters nearly 10,000 molecules in the blood. This includes mobilization and redistribution of cells that recognize and kill cells that are infected with virus. Exercise increases the circulation of immune cells between the blood and the body’s tissues, thereby increasing our “surveillance system” to resist and quickly neutralize infections. Your skeletal muscles, which comprise 30-40% of your body weight, are a major immune supporting organ. When activated, they release myokines to promote production of new immune cells and signal the cells towards areas of infection. To date, there is no data specifically looking at the effects of exercise on coronavirus infection. But there is evidence that exercise can mitigate viral respiratory symptoms and protect the host from other viral infections including influenza (the “flu”), rhinovirus (a cause of the common cold), and herpesviruses such as EBV, VZV, and HSV-1.
Most chronic and degenerative diseases produce (and are then driven by) a “pro-inflammatory” state. To be clear, we need the inflammatory response to properly fight infections. But when this acute response ignites on bed of chronic, low-grade inflammation, the immune response can flare uncontrollably, causing more harm than good. This seems to be the reason that prevalent metabolic diseases worsen symptoms and prognosis of COVID-19. Excess weight, for example produces an excess of pro-inflammatory molecules like interleukin-1 and tumor necrosis factor that over time cause vascular damage, blood sugar dysregulation, and atherosclerosis, the underlying pathophysiology of high blood pressure, diabetes, and heart disease, respectively. After age, obesity is the strongest risk factor for hospitalization from COVID-19. Those with obesity are also likelier to manifest more severe symptoms of the disease and require mechanical ventilation.
Exercise is the best medicine we have for chronic metabolic disease prevention and treatment. Exercise is a cornerstone of any successful and sustainable weight loss strategy. In addition, evidence shows that exercising at moderate to vigorous intensity reduces chronic low-grade inflammation and improves various immune markers in several disease states including cancer, HIV, cardiovascular disease, diabetes, cognitive impairment and obesity
Finally, exercise also directly counters chronic stress, which is skyrocketing these days due to the existential yet invisible threat of COVID-19, mass unemployment, financial fallout, and social isolation. Repeated, chronic activation of the stress response creates an imbalance of cortisol and other stress hormones, which disrupts nearly all of the body’s processes. Over time this can contribute to high blood pressure, hardened and clogged arteries, blood sugar dysregulation, and brain changes that may contribute to anxiety, depression, and dementia. Chronic stress can also trigger overeating, poor sleep, and reduced physical activity—all of which promote excess weight gain.
Ironically and unfortunately, an exercise routine is often the first casualty of increased stress. But this is when we need it most. Exercise is just as effective as prescription medications for reducing symptoms of anxiety and depression. A form of acute stress, exercise directly counters the effects of chronic stress by forcing deep breathing and muscle relaxation. It thereby helps to restore the proper balance of cortisol.
We are still in the midst of the COVID-19 pandemic and the priority must be to stop the spread via social distancing, hand washing, and mask wearing. However, regular physical activity should not be an afterthought. Given its power to help minimize the deleterious effects of the virus, ameliorate our symptoms, and expedite recovery times, it should be a central tenant of a comprehensive risk reduction strategy.
