A summary of what is known to date suggests that obesity is associated with a higher risk of developing severe symptoms and complications of Coronavirus Disease 19 (COVID-19), regardless of other diseases such as cardiovascular disease.
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Early data seems to suggest that people with obesity are more likely to get seriously ill due to COVID-19, the disease caused by the novel coronavirus.
An increasing number of reports have linked obesity to coronavirus mortality, and the Centers for Disease Control and Prevention (CDC) are now listing severe obesity as a risk factor for severe COVID-19. The CDC defines severe obesity as having a body mass index (BMI) of 40 or higher.
However, it is currently unclear why obesity is linked to a more dangerous form of the disease.
To shed light on the situation, a team of experts in Germany, the UK and the US have come together to review the evidence and clarify what we know so far.
Their results are published in Nature Reviews Endocrinology.
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The evidence so far
The article summarizes the preliminary data on obesity and COVID-19.
In China, where the outbreak began, data from 383 patients showed obesity was linked to a 142% higher risk of developing severe pneumonia-related COVID-19.
A larger study of over 4,000 patients with COVID-19 in New York City found that being severely overweight by age is a major risk factor for hospitalization.
In Seattle, a study of critically ill COVID-19 patients found similar results. This analysis found that 85% of obese patients required mechanical ventilation compared with 64% of patients without the condition. Additionally, 62% of obese patients died from COVID-19 compared to 36% of non-obese patients.
It is important to note, however, that this particular study included only 24 patients, all of whom were critically ill, making it difficult to draw far-reaching conclusions from the data.
The final study included in the analysis, which included 124 patients in Lille, France, also found that obese patients were more likely to require invasive mechanical ventilation.
Taken together, the evidence suggests that obesity can be a significant risk factor for COVID-19.
As the lead author of the study, Dr. Norbert Stefan from the German Center for Diabetes Research Medical News Today:
"We have come to the conclusion that obesity puts people infected with the novel coronavirus (SARS-CoV-2) at a very high risk of more severe COVID-19 disease and potentially a risk of death."
Why is Obesity a Risk Factor?
Importantly, the risk seems to be independent of other diseases such as high blood pressure, which are more common in people with obesity.
According to the study's authors, a possibility that obesity may increase the risk of severe COVID-19 is a breathing disorder.
People with obesity are more likely to have higher resistance in their airways, lower lung volume, and weaker breathing muscles, which are critical to fighting off COVID-19. These factors make a person more likely to develop pneumonia and put additional stress on the heart.
Obesity is also linked to diabetes, heart disease, and kidney disease, which also increase the risk of pneumonia.
Aside from these issues, high blood pressure, high cholesterol, and prediabetes could make people more susceptible to infection, the authors said.
The link between diabetes and COVID-19 appears to be particularly important.
"There is data showing that hyperglycemia [high levels of glucose in the blood] is a strong and independent predictor of severe COVID-19 progression, even in the undiagnosed area," explains Dr. Stefan.
Missing BMI data
While this research strongly suggests that obese people are at higher risk associated with COVID-19, there are limitations to its analysis. First, most studies have not yet been peer-reviewed.
Many also failed to provide measurements of patient weight or height, both of which are required to calculate BMI, a universal measure of obesity. The BMI can also be used to estimate the percentage of body fat.
"Most of the articles published in the past 2 months that included data on comorbid conditions that may be associated with an increased risk of severe COVID-19 did not provide data on body fat mass or metabolic health," says Dr. Stefan. In particular, some studies from China and Lombardy, Italy - two of the hardest hit areas - did not provide any weight or size information.
The authors emphasize that future studies should record not only BMI, but waist circumference as well as glucose levels and the hormone that regulates it, insulin. These measurements can help determine if a person has insulin resistance or prediabetes, which may contribute to a higher risk of COVID-19 in people who are obese.