It’s not so often that such an obvious study is done.
It’s obvious that healthy sleeping and exercise habits are important lifestyle factors that support the immune system and prevent diseases. It may be so obvious that coronavirus research thus far seldom considers confirming it. At least, I rarely see studies examining how lifestyle factors interact with Covid-19.
One such study was published in Nature and Science of Sleep, a reputable journal, titled “Reduced Sleep in the Week Prior to Diagnosis of COVID-19 is Associated with the Severity of COVID-19.” The title alone is probably sufficient as a take-home message. But this piece will dissect the study further and provide more context.
What the study did and found
Researchers in China traced back health records of hospitalized patients with Covid-19 across multiple hospitals from three different China provinces. Then they called the patients to inquire about their personal information such as age, sex, weight, physical activity, and sleep. In sum, 164 people infected with Covid-19 (who were discharged from the hospital) and 188 uninfected responded.
Using both the health records and phone interview data, the study identified several independent risk factors of getting Covid-19 and severe Covid-19. (By independent, it means factors that are not influenced by other factors.) These include smoking history, medical comorbidities, irregular exercise, sedentary lifestyle, overexertion, and reduced sleep.
Specifically, those who did not exercise regularly (less than three times per week) had a 2.9-times increased risk of severe Covid-19. Interestingly, 91% of asymptomatic infections happened to those who exercised regularly, which means they didn’t get sick despite contracting the coronavirus. Moderate intensity exercises provided the maximal benefit.
Even animals intuitively sleep more when they are fighting infections. Sleep deprivation studies in humans or animals, in turn, always leads to worse health outcomes from, as well as increased risk of, infections.
About sleep, 7–9 hours were defined as adequate. Notably, the sleep status was determined during the week before the Covid-19 diagnosis. Analyses revealed that the “risk of severe infection increased with decreased sleep status, reaching [6.7-times] higher for potentially appropriate sleep and peaking at [8.6-times] higher for lack of sleep…,” the study authors wrote. Moreover, “the possibility of developing damage of external lung organs [as a result of Covid-19] decreased with increases in average daily sleep time.”
More context on exercise
A prior study in May 2020 utilizing the U.K. biobank data of 387,109 adults has also found physical inactivity as an independent risk factor for Covid-19 hospitalization— with a population attributable fraction (PAF) of 8.6%. This means 8.6% of Covid-19 hospitalizations could have been prevented if the factor was addressed. Fortunately, even less exercise (<150 minutes per week) also conferred benefits in lowering hospitalization risks. This study has also calculated the PAFs of other factors and how the overall ‘lifestyle score’ affects hospitalization risks, as detailed here:
Many other population studies — with sample sizes ranging from about 30,000 to 100,000 — have also supported regular exercise as a protective factor against risks of future infections, such as bloodstream infections (and sepsis), pneumonia, and overall bacterial- and viral-induced deaths.
To restate, moderate-intensity exercise was found to be the most beneficial in the study described above, compared to low-, high-, or no-intensity. Studies involving athletes also agree that moderate levels of physical activity are most optimal in attenuating the risks of respiratory infections.
This means 8.6% of Covid-19 hospitalizations could have been prevented if the factor was addressed. Fortunately, even less exercise (<150 minutes per week) also conferred benefits in lowering hospitalization risks.
It’s estimated that only one-fourth and one-fifth of American adults and high-schoolers, respectively, get enough exercise. Exercise is a primary protective factor against chronic diseases — e.g., diabetes, obesity, cancer, cardiovascular diseases, depression, anxiety, and others— which are “the major killers in the modern era.” Advancing civilization has allowed “modern humans [to] engineer most physical activity out of daily life,” Frank W. Booth, a nutrition and exercise physiology professor, and co-workers stated. “Humans now have a choice not to be physically active.”
More context on sleep
It’s general advice to rest well to recover from infections, and that means more sleep. Even animals intuitively sleep more when they are fighting infections. Sleep deprivation studies in humans or animals, in turn, always lead to worse health outcomes from, as well as increased risk of, infections.
For example, in a study of 56,953 middle-aged nurses without major medical comorbidities, those who habitually sleep 5 hours or less or 9 hours or more were more likely to contract pneumonia. Similar findings were reported in another study of 22,726 American adults, where sleeping 5 hours or less doubled the risk of influenza, pneumonia, or an ear infection.
Another notable point is long-term sleep loss does the immune system more harm than short-term sleep loss. In fact, the latter might even enhance immunity, as shown in animal tests. “Evolutionarily, this might be explained by the fact that the host defense system needs to be enhanced in a situation of acute total sleep loss (such as being hunted by a predator) but that without sleep, the immune system eventually fails,” Nigel Curtis, a professor of pediatric infectious diseases, and co-workers stated.
More than one-third of American adults don’t sleep enough. Shift work, pressured lifestyle, and other societal stressors may be to blame. “Because the immune system protects against both infection and [cancer], as well as enables immunization against disease, the concept that the behavior of modern society might compromise immunity has far-reaching public-health implications for both individuals and the population as a whole.”
It’s common advice to exercise and sleep well, so the immune system can function as it should and ward off diseases. Indeed, a study in China has found that physical inactivity and sleep deprivation increase the risk of more severe Covid-19 by several folds. Similarly, a study in the U.K. has calculated that exercise could have prevented 8.6% of hospitalizations for Covid-19. These results are in line with many prior large, population-level studies showing that sufficient exercise and sleep prevent life-threatening infections. Yet, as a result of drastic societal changes, chronic sleep loss and lack of exercise have become the norm.