As the COVID-19 pandemic seems to be slowing down in some parts of the world slightly but accelerating in others, scientists are investigating the role played by a host of factors that might impact the final outcome. A new study published on the preprint server medRxiv* in May 2020 examines the role of abdominal fat (visceral obesity, VO) in severe COVID-19.
The Aim of The Current Study
The researchers used computed tomography (CT)-based measurements of visceral and subcutaneous fat to assess the presence of obesity and compare it with the severity of COVID-19 disease.
Obesity has been suggested, in light of previous research, to be a risk factor for severe COVID-19. However, the distribution of body fat is almost as important as obesity itself in determining cardiometabolic risk.
Visceral or abdominal fat is linked to metabolic syndrome, increasing the risk of cardiovascular disease and type 2 diabetes, and subsequent risk of various medical conditions. Though body mass index is routinely used as a screening tool for obesity in adults, it cannot sensitively identify excessive fat mass, nor can it tell where the fat is located.
The current study was aimed at accurately assessing visceral and subcutaneous fat to help describe the distribution of body fat in a dependable manner.
Assessing Visceral Fat Vs. BMI and COVID-19 Severity
They performed a retrospective analysis of 30 patients, all of whom had confirmed COVID-19 by laboratory testing, with a mean age of 66 years, from a single center in Berlin, Germany. The confirmatory test was polymerase chain reaction (PCR) on nasopharyngeal or deep nasal swabs, performed at the time of admission.
Severe COVID-19 was defined by any of the following criteria: hospitalization in the intensive care unit (ICU), with the need for a ventilator. All patients were also examined for abdominal fat at the level of the first lumbar vertebra using low-dose chest CT.
The investigators found that the risk of severe COVID-19 was increased by the presence of abdominal fat and was proportionate to the increase in upper abdominal circumference. ICU admission was required for 43% of patients during treatment, with men being affected more often than women in the current study. Of the 13 ICU admissions, 7 eventually had to be put on ventilators, 6 of them being men.
A regressive analysis showed that for each increase in VFA by 1 dm2, the risk for ICU admission went up by 23 times, and for mechanical ventilation by 16 times, adjusted by sex and age. With the upper abdominal circumference, the increase by one centimeter was related to a 1.1-fold increase in risk for ICU admission and 1.25 fold for mechanical ventilation.
The mean BMI for all patients was 26, with a mean of 26 for men and 28 for women. However, the BMI was higher for patients admitted to the ICU at 27 compared to non-ICU patients at 26, though this was not significant.
Visceral fat area (VFA) was significantly higher in men (0.95 dm2) compared to women, and higher than the median (0.82 dm2) in all patients. The total fat area was higher in ICU patients compared to others, and VFA was much larger at 1.12 dm2 vs. 0.7 dm2 in non-ICU patients. This difference was also observed concerning upper abdominal circumference at 107 cm for ICU patients vs. 99 cm for non-ICU patients.
Patients on ventilators also had a higher VFA at 1.24 dm2 compared to patients who could breathe freely (0.77 dm2). The corresponding upper abdominal circumference was 110 cm vs. 100 cm, respectively.
There was a moderate correlation between VFA and BMI, higher for men than for women, and for upper abdominal circumference and BMI, again higher for men than for women, though not by much.
The Implications of the Study
Considering a large number of obese adults at nearly 650 million worldwide, this could lead to an alarming increase in risk for severe COVID-10 in the Western Hemisphere, where obesity is an epidemic condition. The use of VFA rather than BMI to assess body fat distribution improves the accuracy of the correlation of COVID-19 severity with body fat.
The underlying mechanism may relate to the low-grade inflammation that persists in obesity, and which promotes the development of metabolic dysfunctional conditions such as dyslipidemia or type 2 diabetes mellitus, besides immune dysfunction, which may facilitate infection risk. Visceral obesity is also the chief risk factor for many other disorders, such as cardiovascular disease.
This is the first study that identifies explicitly visceral fat and upper abdominal circumference as the most important factors for severe COVID-19 disease. The study suggests that “CT-based quantification of visceral adipose tissue and upper abdominal circumference in routinely acquired chest CTs may, therefore, be a simple tool for risk assessment in SARS-CoV-2-patients.”
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.