Obesity and overweight have been called out as risk factors for COVID-19 since the early days of the pandemic, and research continues to suggest that carrying excess weight could raise your risk of COVID complications and death. Even mild obesity may raise the risk of COVID-19 severity, calling into question current United Kingdom guidelines that only classify severe obesity as a risk factor.
The new finding was revealed by researchers from the Alma Mater Studiorum University of Bologna in Italy, who analyzed 482 COVID-19 patients hospitalized between March 1 and April 20, 2020.1 "Obesity is a strong, independent risk factor for respiratory failure, admission to the ICU and death among COVID-19 patients," they wrote, and the extent of risk was tied to a person's level of obesity.
'Mild' Obesity Increases Risk of Severe COVID-19 Illness
The researchers used body mass index (BMI) to define obesity in the study, and although BMI can be misleading in determining whether or not you're at a healthy body weight, in part because it does not take muscle mass into account. It's the most commonly used measurement for defining obesity.
If your BMI is between 25 and 29.9, you are considered overweight and anything over 30 is considered obese. However, obesity is often divided into categories, with class 1 defined as a BMI of 30 to < 35, class 2 as a BMI of 35 to < 40 and class 3 defined as a BMI of 40 or higher, and considered "extreme" or "severe" obesity.2
The U.K.'s National Health Service states that you may be at moderate risk from coronavirus if you are "very obese" with a BMI of 40 or above,3 but the featured study found increased risks started at a BMI of 30, or "mild" obesity.
"Health care practitioners should be aware that people with any grade of obesity, not just the severely obese, are a population at risk," lead study author Dr. Matteo Rottoli said in a news release. "Extra caution should be used for hospitalized COVID-19 patients with obesity, as they are likely to experience a quick deterioration towards respiratory failure, and to require intensive care admission."4
Specifically, patients with mild obesity had a 2.5 times greater risk of respiratory failure and a five times greater risk of being admitted to an ICU compared to nonobese patients. Those with a BMI of 35 and over were also 12 times more likely to die from COVID-19.5
"Whereas a BMI ≥ 30 kg/m2 identifies a population of patients at high risk for severe illness, a BMI ≥ 35 kg/m2 dramatically increases the risk of death," the researchers explained.6
A July 2020 report7 by Public Health England also describes the results of two systematic reviews,8 one of which showed that excess weight worsened COVID-19 severity, and the other that obese patients were more likely to die from the disease compared to non-obese patients.
Compared to healthy weight patients, patients with a BMI above 25 kg/m2 were 3.68 times more likely to die, 6.98 times more likely to need respiratory support and 2.03 times more likely to suffer critical illness. The report also highlights data showing the risk of hospitalization, intensive care treatment and death progressively increases as your BMI goes up.
Obesity, Metabolic Syndrome Linked to Severe COVID-19, Flu
Additional research has also tied obesity and metabolic syndrome — a cluster of conditions including excess abdominal fat, high blood pressure, insulin resistance and lipid abnormalities that increase the risk of heart disease, stroke and Type 2 diabetes — with more severe viral infections.9
Obesity is known to double the risk of influenza,10 for instance, and increases the duration of stay in the ICU along with the need for invasive mechanical ventilation during such infections.11 And obesity is one of the primary causes of metabolic syndrome. According to an article published in the Journal of Virology:12
"Viruses can metabolically engineer host cells by manipulating gene expression and lipid metabolism to enhance viral replication and progeny release while enabling the virus to evade host immune responses. Because metabolic disorders impair immune responses at homeostasis, viral infection further compromises these responses and potentiates metabolic disease severity."
As for how obesity raises risks during viral infections, the chronic, low-grade inflammation it causes is a likely factor. In fact, inflammation triggered by obesity may be responsible for a threefold greater risk of pulmonary embolism (blood clots in the lungs) in COVID-19 patients who are obese,13,14 according to separate research.
The Journal of Virology researchers also suggested that dysregulated lipid synthesis triggered by obesity may aggravate inflammation in the lungs, contributing to increased disease severity during respiratory viral infections.15 As for SARS-CoV-2, the virus that causes COVID-19, they cited one study that found nearly 50% of hospitalized COVID-19 patients were obese and admitted into ICU in need of mechanical ventilation.
"This is not surprising because excess body weight and fat deposition apply pressure to the diaphragm, which further increases the difficulty of breathing during a viral infection," they wrote.16 Additional mechanisms are also suggested for how obesity increases COVID-19 severity, including:17
- Increasing leptin resistance and lipotoxicity, as the accumulation of lipids may be exploited by viruses to enhance viral entry and replication
- A combined effect of chronic systemic inflammation and the induction of a cytokine storm