A recent study published in PLoS ONE assessed the association of smoking with coronavirus disease 2019 (COVID-19) complications.
It has been reported that tobacco use and smoking are associated with cardiorespiratory injury, characterized by alveolar damage, autonomic dysregulation, endothelial dysfunction, and reduced lung capacity. Individuals who smoke are more susceptible to respiratory diseases than non-smokers.
However, it remains unclear whether smoking aggravates the adverse consequences of COVID-19. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection causes extra-pulmonary injury besides pneumonia and acute respiratory distress syndrome (ARDS). The implications and impact of smoking on the clinical severity of COVID-19 are poorly understood.
About the study
In the present study, researchers investigated the effects of smoking on COVID-19 severity among hospitalized patients in the United States. Data were extracted from the American Heart Association (AHA) COVID-19 cardiovascular disease (CVD) registry. Patients aged 18 years or older hospitalized for COVID-19 between January 14, 2020, and March 31, 2021, were included in the study.
They included patients with valid information about admission/discharge dates, age, sex, and medical history. Patients with unknown discharge status and those who left against medical advice. The team classified patients as current smokers if they self-reported smoking at admission. Those who reported using e-cigarettes were deemed smokers. Smoking history and other information were not collected.
The study’s primary outcome was severe COVID-19, that is, the use of mechanical ventilation or in-hospital death. The secondary outcome was major adverse cardiac events (MACE), i.e., the occurrence of any of the following during hospitalization: heart failure, acute myocardial infarction, ischemic stroke, cardiogenic shock, myocarditis, or death by acute myocarditis heart failure, or stroke. Age, race/ethnicity, sex, past medical history, risk factors, medication use, and admission time frame were covariates.
Risk factors included diabetes mellitus, obesity, dyslipidemia, and hypertension. Prior medical history included peripheral artery disease, venous thromboembolism, heart failure, stroke, chronic kidney disease, and coronary artery disease. Time-frame of admission was split into five quarters (four quarters of 2020 and the first quarter of 2021).
Past medications included anticoagulants and anti-platelet therapy. Odds ratios (ORs) were computed using two multivariable logistic regression models. Models were adjusted for risk factors, demographics, admission time, and medications. Because demographic and medical history variables of smokers and non-smokers were significantly different, the team carried out propensity score matching to limit confounding.
The final analytic sample comprised 6717 patients with 2239 smokers and 4478 non-smokers. After matching, no significant differences were observed between smokers and non-smokers in sex, age, medication use, and medical history.
The proportion of smokers that survived COVID-19 (32%) was lower than those who succumbed (40%). Deceased patients were older than survivors, more likely males, with a past medical history. Notably, the prevalence of obesity among the deceased patients was less. The proportion of patients who used medication (anti-platelet therapy or anticoagulants) was higher among the deceased patients.
Mechanically ventilated patients were more likely to be smokers, males, obese, and non-Hispanic, with a history of diabetes, dyslipidemia, hypertension, chronic kidney disease, heart failure, and using anti-platelet therapy at admission time. Significantly higher odds of using a mechanical ventilator or mortality were noted for smokers. Smokers also had significantly higher adjusted odds of death or mechanical ventilator use.
Smoking was a stronger risk factor for mortality in those aged 18 – 59 than older adults (> 60 years). Smoking also increased the risk of mechanical ventilation in females and non-Hispanics. In the secondary outcome analysis, the authors found that smokers had higher odds of MACE. Smoking was associated with elevated odds of MACE in those who were female, obese, White, and those aged < 60.
The association between smoking and severe COVID-19 outcomes was significant when smokers were compared to (propensity-score) matched non-smokers. The relationship was also significant when demographic and other variables were adjusted, indicating that smoking was associated with higher COVID-19 severity independent of sex, race, age, and medical history.
However, younger patients had a higher impact of smoking on more severe outcomes than older adults. Patients who were White, female, diabetic, obese, or those with chronic kidney disease had greater odds of death, indicating that smoking caused an additive effect on already existing comorbidities or vulnerabilities.
Of note, the researchers could not differentiate between former and never smokers due to the unavailability of complete smoking history. The smoking status was self-reported and not verified independently. In conclusion, the study observed that smoking was strongly associated with elevated risks of severe COVID-19 outcomes, independent of medical history and sociodemographic characteristics.