Two new, large studies from England and Mexico provide new details on obesity as a risk factor for poor COVID-19–related outcomes, including death, with the UK study noting the highest hospitalization rate in young adults.
Hospitalization, ICU admission
In the first study, published yesterday in The Lancet Diabetes & Endocrinology, University of Oxford researchers extracted data from the QResearch database for nearly 7 million English patients 20 years and older with available body mass index (BMI) values registered at an eligible general practice from Jan 24 to Apr 30, 2020.
It is the largest study to date assessing body weight and COVID outcomes.
Of 6,910,695 eligible patients with a mean BMI of 26.8 kg/m2, 0.20% were hospitalized, 0.02% were admitted to an intensive care unit (ICU), and 0.08% died after they were diagnosed as having COVID-19. Roughly one third of patients with severe coronavirus outcomes had type 2 diabetes, and most were 60 years or older.
Starting at 23 kg/m2, BMI was associated with coronavirus-related hospitalization (adjusted hazard ratio [aHR], 1.05) and, starting at 28 kg/m2, death (aHR, 1.04). There was a linear association across the entire BMI range for ICU admission (aHR, 1.10).
According to the US Centers for Disease Control and Prevention, a BMI of 23 mg/k2 is considered normal, but 28 kg/m2 is considered overweight.
The researchers found a significant link between BMI and age, with higher HRs for hospitalization above a BMI of 23 kg/m2 for patients 20 to 39 years old (aHR, 1.09), compared with no association for those 80 to 100 (aHR, 1.01). Similarly, Black patients had a higher risk of hospitalization than White patients (aHR, 1.07 vs 1.04).
The risk of COVID-19–hospitalization and ICU admission tied to increasing BMI was slightly lower in patients with type 2 diabetes, high blood pressure, and cardiovascular disease than in those with no underlying medical conditions.
The authors noted that even a small increase in BMI over 23 kg/m2 increased the risk of poor COVID-19 outcomes. "People with excess weight, even without other comorbidities, are at substantially increased risk of admission to hospital and ICU and death due to COVID-19, especially for younger adults and Black people," they wrote.
"Excess weight is a modifiable risk factor, and investment in the treatment of overweight and obesity and long-term preventive strategies could help reduce the severity of COVID-19 disease."
Co-senior author Paul Aveyard, PhD, said in a Lancet news release emailed to journalists, "We don't yet know that weight loss specifically reduces the risk of severe COVID-19 outcomes, but it is highly plausible, and will certainly bring other health benefits."
In a commentary in the same journal, Krishnan Bhaskaran, PhD, of the London School of Hygiene & Tropical Medicine, said that BMI is now being used in risk-prediction tools that inform vaccine prioritization, underscoring the importance of understanding the link between BMI and COVID-19 outcomes in informing public policy.
"Key future research priorities will be to establish whether BMI affects vaccine efficacy, and to understand whether people outside the BMI range considered to be healthy (18.5–24.9 kg/m2) are at increased risk of post-COVID-19 sequelae," he wrote.
"Further careful epidemiological study of these and other emerging questions will inform the ongoing public health response to this new disease that is likely here to stay."
In a commentary on the Science Media Centre website, Naveed Sattar, MD, PhD, of the University of Glasgow, said of the study, "These data add to the overwhelming evidence from other sources (several hundred studies now in many parts of the world) that support excess body weight are an important, causal risk factor for more severe COVID-19 outcomes."
Obesity alone, in combination with other comorbidities
The second study, led by researchers at the Instituto Nacional de Ciencias Medicas y Nutricion and the Instituto Nacional de Cardiologia Ignacio Chavez in Mexico City, was published today in Epidemiology & Infection.
The national observational study involved analyzing data from 15,529 COVID-19 inpatients and outpatients in Mexico's 32 states from the National COVID-19 Epidemiological Surveillance Study between Feb 24 and Apr 26, 2020.
The case-fatality rate was 9.2%, and 21% of hospitalized patients died. Obesity alone almost tripled the risk of death (aHR, 2.7), while obesity combined with other underlying illnesses increased the risk of death and other severe outcomes even further (diabetes HR, 2.79; immunosuppression HR, 5.06; high blood pressure HR, 2.30).
Of all COVID-19 patients, 47.8% were 41 to 60 years old, which the researchers said shows that many younger Mexican patients were infected early in the pandemic.
The authors observed that Mexicans are metabolically distinct from Asians and Europeans in that they are more likely to have early-onset overweight or obesity. In addition, overeating, especially of highly processed foods, has led to an obesity epidemic in Mexico in recent decades, with 75.2% of the population older than 20 years either overweight (39.1%) or obese (36.1%).
"Thus, the toll of COVID-19 could be higher in Mexico by affecting younger people compared to populations with a lesser burden of disease among young adults," they wrote.
Of all underlying illnesses, obesity was most strongly tied to COVID-19 infection in Mexicans with mostly symptomatic illness. "Obesity alone and in combination with other comorbidities was a significant risk factor for secondary outcomes (pneumonia, hospitalization, [invasive mechanical ventilation], and ICU admission) in patients positive for SARS-CoV-2," the researchers concluded. "The risk conferred by obesity increases when it is present alongside other comorbidities, particularly, [diabetes], hypertension, and immunosuppression."