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Being Fit Protects You From Severe Covid-19 in a Dose-Dependent Manner

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 20 days ago

Half of the Covid-19 hospitalizations could’ve been prevented by fostering a healthy lifestyle.
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Mark Hamer, a professor of sport and exercise medicine, and his colleagues at UK institutions recently had their paper, “Lifestyle Risk Factors, Inflammatory Mechanisms, and COVID-19 Hospitalization: A Community-Based Cohort Study of 387,109 Adults in UK,” published in the Brain, Behavior, and Immunity journal.

This is the first study to investigate how much do health behaviors affect the risk of being hospitalized for Covid-19, as well as how many cases could have been averted if at-risk individuals fostered a healthier lifestyle.

Poor Lifestyle Score

The study recruited 387,109 people from the UK Biobank study, of whom 760 (0.2%) were hospitalized for Covid-19. Analyzing the health behaviors of these 760 patients, they found that a lifestyle score of ≥5 lead to a 4.41-fold increased risk — or 4.41 times as likely — for hospitalization.

The poor lifestyle score is calculated based on:

  • Smoking history (0=never; 1=past; 2=current).
  • Physical activity (0=meeting guidelines; 1= active but below guideline; 2=sedentary). Guidelines were ≥150 minutes/week of moderate-to-vigorous physical activity or ≥75 minutes/week of vigorous activity.
  • Alcohol (0= intake within guidelines; 1= never or very occasional exceeding guidelines; 2= intake exceeding guidelines). Guidelines were <14 units in women and <21 units in men.
  • Obesity or BMI >30 (0=healthy weight; 1=overweight; 2 = obese).

A poor lifestyle score of ≥5 would look like an overweight person who drinks a lot of alcohol, rarely exercises, and smokes cigarettes (1+2+1+2=6). Or it could be an ex-smoker who is inactive, overweight, and sometimes a heavy drinker (1+2+1+1=5).

To reiterate, a poor lifestyle score of ≥5 increased the risk of severe Covid-19 in need of hospitalization by >4 times compared to the optimal lifestyle score of 0. And this effect is dose-dependent with poor lifestyle scores of 1, 2, 3, and 4 leading to 1.58 times, 2.73 times, 2.76 times, and 3.12 times increased risk, respectively.
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Individual Lifestyle Factor

Professor Hamer et al. then looked at each health behavior individually. Adjusting for age, sex, and each health behavior (to avoid overlapping or compounding effects), they calculated that:

  • Physical inactivity increased hospitalization risk by 1.32 times.
  • Smoking increased hospitalization risk by 1.42 times.
  • Obesity increased hospitalization risk by 2.05 times.
  • Heavy alcohol intake, alone, did not increase hospitalization risk.

Population Attributable Fraction (PAF)

PAF refers to the measure of how many cases could be averted if at-risk individuals modified their risk. A PAF of 10%, for example, means that 10% of cases could have been avoided if the risk factor was addressed earlier. In this case of Covid-19 hospitalization:

  • PAF of active smoking was 13.3%.
  • PAF of physical inactivity was 8.6%.
  • PAF of overweight or obesity was 29.5%.
  • PAF of the three combined was 51.4%.

This means that, in the UK Biobank cohort, poor lifestyle choices of cigarette smoking, sedentary behavior, and being overweight/obese contributed to over half of Covid-19 hospitalizations. Put it the other way, half of the severe Covid-19 cases could have been avoided by cultivating a healthier lifestyle.
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Underlying Mechanism

The current study also examined the levels of C-reactive protein (CRP), a marker of chronic, low-grade, pro-inflammatory state. For each quintile increase in CRP levels, there was a dose-dependent increase in the risk of hospitalization — i.e., 1.18, 1.32, 1.48, and 1.47 times, respectively.

Adjusting for CRP levels blunt the effect estimates of the lifestyle score on the hospitalization risk by 10–16% — “suggesting a possible mediating effect,” the authors wrote. This finding indicates that the reason unhealthy behaviors increase the risk of severe Covid-19 is, partly, due to unresolved chronic, low-grade inflammation in the body.

A Few Things to Consider

As with any other studies, results should be interpreted in light of its limitations:

  1. Baseline health behaviors were measured during the UK Biobank study in 2010. Some participants may have reversed their behavior after that. The heavy alcohol consumption group that had no increased risk of hospitalization, for example, may have “stopped drinking due to prescribed medication and underlying health conditions,” the authors speculate.
  2. Some covariates were not controlled for — i.e., disease comorbidity, education, and ethnicity.
  3. Cases of Covid-19 being treated outside of hospitals were not studied.
  4. This study is observational and not interventional, so the calculated PAF may be an overestimate.

To Wrap Up

In this cohort study in the UK, unhealthy lifestyle choices is a major risk factor for severe Covid-19 in need of hospitalization. Being overweight or obese was the greatest risk factor, followed by smoking and sedentary behavior. Heavy alcohol consumption, by itself, was not a risk factor in this study.

However, the overall fitness— encompassing weight, smoking, exercise, and alcohol — has a compounding or cumulative effect on the risk of Covid-19 hospitalization. And this is partly due to the underlying chronic, low-grade inflammation. Importantly, the risk is dose-dependent; more unhealthy behaviors lead to greater risk.

Looking at the bright side, it also means that a healthy lifestyle could prevent cases of severe Covid-19 by about 50% of the time, as shown by the PAF score. “Adopting simple lifestyle changes could lower the risk of severe COVID-19 infection,” Professor Hamer and his team concluded.

This article was originally published in Microbial Instincts with minor modifications.