Exercise and Your Immune System

Exercise benefits your immune system. But not everybody believes this. Studies in the 1980s and 1990s suggested that a bout of vigorous exercise causes a temporary loss of immune cells in the blood. Researchers thought this period with reduced immune cells creates an “open window” during which you’re more susceptible to pathogens. This theory is wrong.

Exercise and Your Immune System

It is true that blood tests among athletes show a reduction in immune cells one to two hours after exercise. But there is a new reassessment of the evidence by John P. Campbell and James E. Turner. They found the reduction results not from an absence of immune cells but from their redeployment. After exercise, the immune cells move from the bloodstream to other tissues for immunological surveillance. You could say that, far from reducing immunity, a single bout of vigorous exercise heightens it, or at least makes it more focused and responsive. 

A study that just came out reported on the differences in immune reactions between regularly exercising mice and sedentary mice. Researchers infected the mice with a pathogen, and the exercising mice fared significantly better. What’s most interesting about this study, however, is that immunofluorescence showed that immune cells clustered around the pathogens in the exercising mice and were more diffuse in the sedentary ones. This confirms the idea that exercise depletes the blood of immune cells in order to redeploy them where they might be most needed.

Where the “Open Window” Comes From

The idea of the “open window” first emerged from studies of athletes who self reported sniffles after athletic events. But developing short-lived sniffles after a marathon or a bike race is less likely the result of infection than of environmental exposure. If you race, you may know such sniffles, particularly in winter, when the air is dry and hard breathing gives you a raw throat. And it’s even more likely in the spring, when pollen can irritate your breathing passages. But these kinds of sniffles rarely last more than a few hours.

Too many people still consider the “open window” hypothesis to be valid. Some even regard it a matter of common sense. But here’s more from the Campbell and Turner reassessment. They described a battery of studies that showed a single bout of vigorous exercise actually increases the body’s response to a vaccine during the so-called “open window.” You would think that response to a vaccine is one of the best indicators of a healthy immune system.

Furthermore, the enhanced immunity provided by vigorous exercise confers protection, not just from infection (bacteria and viruses) but also from noninfectious diseases like cancer and diabetes. Regular exercise reduces chronic inflammation, which is now recognized as a major factor in aging and noninfectious disease, particularly so-called “lifestyle diseases.”

Exercise Curbs Immunological Aging

Most of us have learned from the advent of Covid-19 that the immune system weakens with age. This is the reason that the elderly are considered to be at higher risk in the current pandemic. Clinical research shows declines in T cells and other immune factors among the aging. But epidemiological studies also show that immunity improves with physical activity, particularly regular, structured exercise.

On the subject of immunological aging, I’ll give the last word to Campbell and Turner. They wrote, “We conclude that leading an active lifestyle is likely to be beneficial, rather than detrimental, to immune function, which may have implications for health and disease in older age.”

Bottom line: keep exercising. Even if you’re under a stay at home order. Especially if you’re under a stay at home order.