Data indicate that, depending on the degree of obesity, patients with obesity who are infected with COVID-19 have a 1.3- to 7.4-fold increased risk of requiring critical care when compared with patients who aren’t obese, suggesting that body fat accumulation may be linked with greater infection severity and poor clinical outcomes, according to Rocky Strollo, MD, PhD. With BMI not able to discriminate between fat and lean body mass and thus poorly reflecting body fat distribution, Dr. Strollo, Sofia Battisti, MD, PhD, and colleagues conducted a study—published in Diabetes Care—to assess the relationship between abdominal fat distribution and COVID-19 severity based on the hypothesis that excess visceral adipose fat (VAT) is associated with COVID-19 severity.
Testing the Hypothesis
“VAT and subcutaneous adipose fat (SAT) were measured by computed tomography in 441 subjects consecutively evaluated in the emergency department for a clinical suspicion of COVID-19 between February 26 and April 6,” explains Dr. Strollo. Among participants, 144 had COVID-19 pneumonia, 42% of whom were admitted to the ICU (ICU-COVID-19 group). Also included were 136 patients with clinical suspicion of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection who tested negative by nasopharyngeal swab and had no high-resolution CT (HR-CT) signs of pneumonia (non-COVID-19); this group served as controls. Excluded from analyses were 161 patients with unavailability of reverse transcription-polymerase chain reaction (RT-PCR) data or absence of HR-CT signs of pneumonia despite a positive RT-PCR.
For the study, SAT was defined as the greatest thickness between the skin-fat interface and muscle wall and VAT as the greatest distance between the inner muscular wall and the anterior liver surface. The primary exposure and outcome measures were VAT amount—as identified by an increased VAT to SAT ratio (VAT/SAT)—and admission to the intensive care unit (ICU), as a measure of COVID-19 severity, respectively. No differences in age or BMI occurred between patients with COVID-19 and controls.
Increased ICU Admission Risk
“Our data indicate that abdominal fat distribution characterized by increased visceral and lower subcutaneous fat increased the risk of ICU admission for COVID-19, independent of BMI,” says Dr. Stollo. “Visceral fat was associated with increased risk of ICU admission (age-, sex-, and BMI-adjusted OR [aOR] for unit [mm] increase, 1.16; 95% confidence interval, 1.07–1.26; P<0.0001).” (Table)
Although BMI was higher in ICU-COVID-19 patients than in those not requiring intensive care (nICU-COVID-19) and BMI was positively correlated with VAT and SAT independently, it was unrelated to VAT/SAT ratio. Overall, patients with COVID-19 had thicker VAT than controls, with the difference driven by the ICU-COVID-19 group and suggesting that visceral adiposity influences COVID-19 severity. “ICU-COVID-19 patients had 30% thicker visceral fat than nICU-COVID-19 and non-COVID-19 patients,” adds Dr. Strollo. “Subcutaneous fat was 30% lower in ICU-COVID-19 patients than in nICU-COVID19, suggesting that patients with severe COVID-19 have a different body fat distribution than those with non-severe COVID-19.”
Improved Risk Stratification
“Additional research is needed to understand whether fat distribution can predict mortality in patients with COVID-19,” says Dr. Strollo. “A direct role of adipose tissue in disease pathogenesis should be clarified. While enterocytes represent a potential entry site for SARSCoV-2, it is unknown whether virus recognition by the gut immune system may trigger an immune-inflammatory response spreading to mesenteric visceral fat and exacerbate local inflammation.”
In the meantime, with fat distribution characterized by increased visceral and reduce subcutaneous fat shown in the study to be per se a risk factor for COVID-19 severity (ICU admission) independent of the degree of obesity defined by BMI, he suggests that evaluation of fat distribution by CT or other methods (eg, waist circumference) may increase the risk stratification of patients with COVID-19. “Imaging can help analyze age- and gender-related differences in the body,” adds Dr. Battisti. “We should look into images acquired during this pandemic with a different point of view, for example identifying age, race, and gender modifications with imaging as a biomarker of osteoporosis, obesity, and body composition.”