Running and Immunity
During this pandemic, many of us are thinking about the strength of our immune system, not only as it fights off Covid 19 but also the countless other organisms constantly trying to attack us. The question often arises about the effect of exercise, such as running, on immunity. Not much research has been done in this area, and some of the findings are conflicting, but below is the latest and best information.
The immune system has two distinct parts: the innate and the adaptive. The innate system is inborn and responds to all intruders in the same way. The adaptive is built up over a lifetime of exposures to various intruders and the many vaccines we have received. One can think of the innate system as the regular army and the adaptive as the elite special forces.
Aging weakens the immune system. But, it is recognized that consistent exercise slows the rate of decline. As a result, a 70-year-old who exercises frequently may have a stronger immune system than a sedentary 40-year-old. All the research confirms the fact that staying in shape with regular aerobic exercise strengthens the immune system and makes us more resistant to invading organisms of all types. The literature typically refers to this as a daily workout of up to 60 minutes of easy to moderate aerobic exercise.
Some studies focus on measuring the white blood cells, primarily neutrophils and macrophages, which engulf and digest invaders that do not belong in the body. Other studies have focused on clinical symptoms after long events such as marathons and ultras. One analysis found that after a 56-kilometer ultra, (about 35 miles) one-third of the runners reported upper respiratory infection symptoms within two weeks of the race. Findings such as this have given rise to the theory of the “open window.” The idea is that for 3 to 72 hours after a strenuous or prolonged workout or race, one has increased susceptibility to illness. Blood studies seem to support this theory since circulating lymphocytes are as much as 40% below baseline during this period. Some authorities contend that the lowered white blood count is not a problem because those cells are out of the bloodstream and, instead, in the body looking for infection to fight. This is called immune surveillance and is exactly what these cells are supposed to do. (On a personal note, I have never become ill after 51 marathons or 4 ultras.)
The bottom line is clear: easy to moderate daily aerobic exercise strengthens and preserves the immune system. The question of the effects of intense or prolonged exercise remains. The answer may be that it also is beneficial if one follows these guidelines: stay hydrated; ingest carbohydrates before, during, and after the event; have a good diet; get adequate rest afterward; and sleep well.