In the first metaanalysis of its kind, published on 26 August in Obesity Reviews, an international team of researchers pooled data from scores of peer-reviewed papers capturing 399,000 patients. They found that people with obesity who contracted SARS-CoV-2 were 113% more likely than people of healthy weight to land in the hospital, 74% more likely to be admitted to an ICU, and 48% more likely to die.
“We didn’t understand early on what a major risk factor obesity was. … It’s not until more recently that we’ve realized the devastating impact of obesity, particularly in younger people,” says Anne Dixon, a physician-scientist who studies obesity and lung disease at the University of Vermont. That “may be one reason for the devastating impact of COVID-19 in the United States, where 40% of adults are obese.”
People with obesity are more likely than normal-weight people to have other diseases that are independent risk factors for severe COVID-19, including heart disease, lung disease, and diabetes. They are also prone to metabolic syndrome, in which blood sugar levels, fat levels, or both are unhealthy and blood pressure may be high. A recent study from Tulane University of 287 hospitalized COVID-19 patients found that metabolic syndrome itself substantially increased the risks of ICU admission, ventilation, and death.
The largest descriptive study yet of hospitalized U.S. COVID-19 patients, posted as a preprint last month by Genentech researchers, found that 77% of nearly 17,000 patients hospitalized with COVID-19 were overweight (29%) or obese (48%).
The physical pathologies that render people with obesity vulnerable to severe COVID-19 begin with mechanics: Fat in the abdomen pushes up on the diaphragm, causing that large muscle, which lies below the chest cavity, to impinge on the lungs and restrict airflow. This reduced lung volume leads to collapse of airways in the lower lobes of the lungs, where more blood arrives for oxygenation than in the upper lobes. “If you are already starting [with] this mismatch, you are going to get worse faster” from COVID-19, Dixon says. Other issues compound these mechanical problems. For starters, the blood of people with obesity has an increased tendency to clot—an especially grave risk during an infection that, when severe, independently peppers the small vessels of the lungs with clots.
Add obesity to the mix, and the clotting risk shoots up. In COVID-19 patients with obesity, Hunt says, “You’ve got such sticky blood, oh my—the stickiest blood I have ever seen in all my years of practice.”