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Immunity and Exercise

Dec 26, 2020

Forget supplements. Forget mega doses of vitamins. Forget homeopathic tinctures. Forget any kind of magic bullet pill. Want a simple, free and most importantly, effective way to best protect yourself during the current pandemic?

Just move.

We all know exercise is good for us on numerous physical and mental levels. But understanding how exercise benefits the immune system, and why you should be physically active on a regular basis is particularly relevant to what is happening in the world today.

Exercise immunology is a relatively new field in terms of scientific study with the majority of published research occurring in the past three decades; yet, the discoveries made within this relatively short time span have been profound. It is now widely accepted that regular exercise positively alters both the number and function of a variety of circulating immune cells in the body.

Innate immune cell (natural killer cell)

In oversimplified terms, our immune system operates on a two pronged approach – an innate response and an adaptive response. The innate immune response is immediate and non-specific, meaning that when a foreign pathogen enters our body (like Covid-19), cells in the innate system quickly launch an attack to kill and help prevent further spread. If the innate cells (comprised of natural killer cells, macrophages, neutrophils, etc.) are unable to control the initial infection, they recruit the adaptive immune cells to launch a more powerful and robust response. Once activated, the adaptive immune cells (which include T-cells and B-cells) have the ability to clone themselves rapidly and effectively within several days. B-cells are responsible for producing the valuable antibodies that specifically target the new invader. The adaptive immune response also adds long lasting ‘memory’ cells to its arsenal, so if the same invader is encountered again, the body is able to launch a rapid, highly specific and potent attack against it.

So how can physical activity boost our ability to fight pathogens? Moderate exercise (a single bout) acutely enhances the functional capacity of innate immune cells, increasing their ability to kill invaders more quickly and effectively. In addition, exercise elicits a dramatic immune cell mobilization and recirculation, where large concentrations of cells travel out of the lymph tissue where they normally reside, and into the bloodstream, where they are then redistributed to more vulnerable infection sites (nose, throat, lungs, and gut for example). This post-exercise response is thought to stimulate the immune system into a temporary heightened state of surveillance and regulation, leading to a boost in the body’s ability to fight viral and bacterial pathogens. Circulating immune cells typically return to normal pre-exercise levels within 24 hours.

Note: Moderate exercise is generally defined as physical activity lasting less than 1 hour at an intensity of ~ 60-75% of maximal heart rate. Think along the lines of your typical 3-5 mile run.

Frequent and regular exercise (not just your daily run, but your repeated weekly mileage and visits to the gym, e.g.) provides further sustained immune benefits primarily through its anti-inflammatory effects. Exercise produces an increase in the circulating amount of anti-inflammatory cytokines, small proteins released by immune cells that act as messengers to other cells in the immune system. Physically active individuals have been shown to possess lower levels of systemic inflammation than sedentary individuals. This is important because chronic low grade inflammation is a known underlying factor in numerous disorders, diseases and infections, some of which include obesity, arthritis, cardiovascular disease, upper respiratory infections, and various cancers. Related to Covid-19 specifically, early studies in hard-hit New York City are finding that after age, obesity is the biggest underlying health condition related to hospital admissions. It is not surprising given the fact that Covid-19 in severe cases is thought to drive an inflammatory ‘cytokine storm’ which can lead to respiratory distress, severe pneumonia and increased mortality. In individuals with existing low grade systemic inflammation, the immune system is already at a disadvantage in fighting the virus when it first comes into contact with the body. Although much more research is needed in this area, the additive inflammation caused by Covid-19, in combination with other co-morbidities that frequently exist alongside obesity (diabetes, hypertension, etc) could be making this population more prone to the dangerous virus-induced cytokine storm.

Note: More is not always better in terms of exercise and immune function. Heavy, exhaustive exercise lasting more than 2 hours has been associated with a possible impaired immune system and increased susceptibility to infectious illness. In the current environment, keep your exercise sessions to an hour or less to be on the safe side. Skip the 15+ mile long runs for now.

With the weather getting nicer outside and the fact that running and walking are perfect social distancing exercises, there has never been a better time to start leading an active lifestyle. If you already fall into this category, there has never been better rationale to stay the course. With the known benefits both acute and regular exercise imparts on the immune system you will be better prepared to handle the future of what Covid-19 may present down the road.

Just move.

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