A new meta-analysis published last month in the British Journal of Sports Medicine found that regular physical activity is associated with a lower risk of Covid-19 infection, hospitalization, and death.

Study details and key findings

For the meta-analysis, researchers analyzed findings from 16 studies published between November 2019 and March 2022 which included 1,853,610 participants who engaged in regular physical activity throughout the Covid-19 pandemic. On average, participants were 53 years old.

Participants engaged in a variety of physical activities, including swimming, cycling, volleyball, running, weightlifting, walking, and pedaling in place. In the analysis, the researchers used the Metabolic Equivalent of Task (MET), which calculates the number of calories burned in each minute of activity.

According to the researchers, the most effective amount of exercise is 500 METs—roughly 150 minutes of moderate exercise or 75 minutes of vigorous exercise each week. However, individuals who exercised less were still more protected against Covid-19 than those who did not exercise at all.

Currently, CDC recommends 150 minutes of moderate intensity exercise a week along with two days of strength training for adults. However, one in four Americans are "inactive," which means that they do not engage in physical activity outside of their day-to-day jobs, according to CDC. 

"Everybody can benefit from being more active, regardless of age, sex or physical ability," noted Yasmin Ezzatvar, a researcher on the study.

When compared with people who were not active, individuals who remained active during the pandemic had an 11% lower risk of being infected by the coronavirus. In addition, they had a 36% lower risk of hospitalization from Covid-19, a 43% lower risk of death, and a 44% lower risk of severe illness.

"There is evidence that regular physical activity might contribute to a more effective immune response, providing enhanced protective immunity to infections, which could explain the relationship between exercise consistency with COVID-19 infection," Ezzatvar added. 

Commentary

According to David Nieman, a professor of health and exercise science at Appalachian State University, who was not involved in the Covid-19 review, "The risk of severe outcomes and mortality from the common cold, influenza, pneumonia — they're all knocked down quite a bit. I call it the vaccine-like effect."

"Your immune system is primed, and it is in better fighting shape to cope with a viral load at any given time," he added.

However, since the studies included in the meta-analysis were observational, the researchers noted that additional research is needed to study the potential benefits regular physical activity may have on Covid-19 response.

Separately, Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco, agreed that more research is needed to identify a causal link between regular physical activity and Covid-19 risk.

"For now, you can't say, 'I'll go to the gym so that I can prevent getting Covid,'" Chin-Hong said.

According to Stuart Ray, an infectious diseases specialist at Johns Hopkins University School of Medicine, it is difficult for scientists to study the effect of physical activity on immunity because exercise cannot be easily measured on a linear scale. "People exercise in many different ways," he noted.

Study participants usually self-report exercise habits, which can make it difficult to eliminate errors. When individuals expect exercise to be beneficial, it can trigger a placebo effect, making it hard for researchers to determine the ideal amount and type of exercise for immune function.

In addition, "there is a huge debate about whether or not too much exercise makes you more susceptible to infection and illness," said Richard Simpson, who studies exercise physiology and immunology at the University of Arizona.

According to Simpson, marathon runners often report getting sick after races, potentially suggesting that too much vigorous exercise could inadvertently overstimulate cytokines and inflammation in the body.

However, early evidence suggests that people who engage in an average amount of exercise may see a protective effect against severe illness.

Ultimately, Ray noted that individuals who cannot exercise regularly should not be too worried. "What helps one person stay healthy compared to another is a complex mix of factors," he said. (Sheikh, New York Times, 9/7; Mikhail, "Well," Fortune, 8/22)