The compelling link between physical activity and the body's defense system

JOURNAL OF SPORT AND HEALTH SCIENCE

We live alongside microorganisms–bacteria, viruses, and whatever bed bugs are. It’s a daily dance, with a bulk of our defense placed on the shoulders of the immune system, which quietly gets the job done until we watch the news and decide it’s time to double down. COVID-19 or not, remember that your daily habits help keep you healthy.

There’s no doubt the immune system is responsive to exercise, but will strengthening your muscles also strengthen your ability to fight an infection?

Today’s paper reviews the dull-sounding, yet oh-so-relevant research on exercise immunology. There’s a lot to unpack in this study, but I’m going to focus on a single aspect due to current concerns. Specifically, the relationship between the amount you exercise and your risk for a respiratory tract infection.

Take a look at the figure above. The “J” shape suggests that a lower risk of getting sick is isolated to just a small window. Little to no exercise put’s you at a normal risk, while heavy exercise actually increases your risk. Much like life in general, the sweet spot is in moderation. This is an oversimplification, of course, because habits like hygiene, sleep, and nutrition are equal players here, but if we dig deeper into the research we consistently see a correlation between exercise and immunity.

One study in this review, for example, found that the number of days with an upper respiratory tract infection (URTI) was 43% lower in people who averaged 5 or more days per week of aerobic exercise for just 20 minutes. Four other studies found that regular physical activity is associated with decreased mortality, and decreased rates of influenza and pneumonia (a trend that four other rodent studies verified).

TAKEAWAY
There’s a notable link between exercise and a robust immune system. On paper, that means fewer upper respiratory infections, with a shorter duration when you do get sick. It also suggests increased protection from influenza and pneumonia. This research found the positive impact of exercise is fourfold: it lowers inflammation, increases circulation of immune cells, diversifies the gut microbiota, and delays immune system aging. Exercise may not be the exclusive tool to prevent infection, but keep moving and your next cold might not be as severe.

That said, it’s possible to over-do it, as heavy exertion (we’re talking 60+ mile weeks) will actually increase your risk of illness. Keep moving, albeit in moderation.