Why is obesity a risk factor for severe COVID-19 symptoms?

elderly overweight man listening to doctor 
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A recent report by the Centers for Disease Control and Prevention indicates that older adults and people of any age who have serious underlying medical conditions—including obesity—may be at higher risk for severe illness from COVID-19.
According to the CDC report, the top three underlying conditions among those hospitalized with COVID-19 were diabetes, chronic lung disease and cardiovascular disease.
While it’s too early in this pandemic to have any strong data to support this, it’s logical to think that many patients with obesity—especially severe obesity with a body mass index over 40—will have other obesity-related health conditions that could be associated with a more severe course of illness with COVID-19.
In general, patients with severe obesity are a more challenging population to manage in the intensive care setting, and may struggle to recover if they develop any severe illness, particularly a respiratory infection like COVID-19.
For example, respiratory function in patients with obesity can be compromised from asthma, restrictive lung disease or obstructive sleep apnea.
Cardiovascular disease is highly prevalent in patients with obesity, and this may mean that those patients will have less physiologic reserve if cardiac complications of COVID-19 develop.
Why is this concerning?
While I haven't seen any data identifying obesity as an independent risk factor or predictor for hospitalization or mortality with COVID-19, it stands to reason that people with obesity would be at higher risk because of their underlying diseases that are strongly associated with obesity.
The majority of patients with obesity have at least one obesity-related comorbidity, and type 2 diabetes and cardiovascular disease are among the most common.
According to the CDC, other underlying diseases include hypertension, hyperlipidemia, chronic kidney disease, cancer or a history of cancer, and non-rheumatoid arthritis.
This list of chronic diseases describes the array of illness we see every day in our patients seeking treatment for obesity.
Why are people with obesity more at risk of developing serious respiratory illness?
The prevalence of pulmonary problems in patients with obesity is higher than for normal weight individuals.
Conditions like asthma, sleep apnea, restrictive lung disease and gastroesophageal reflux-related pulmonary issues all compromise the baseline pulmonary function of patients with obesity, and will likely put them at some increased risk for serious illness with COVID-19. 
Again, there are many unanswered questions about specific risk factors that we don't know yet, but I think it’s safe to say that patients with obesity and comorbidities that compromise their heart or lung function are likely going to be at higher risk for developing severe disease with COVID-19, much like the non-obese patients with those risk factors.
Stacy Brethauer is a bariatric surgeon at The Ohio State University Wexner Medical Center and a professor at the Ohio State College of Medicine. He’s also a past-president of the American Society for Metabolic and Bariatric Surgery.