- 78% of people hospitalised for Covid-19 have obesity or overweight, according to a new CDC report.
- Evidence suggests the more severe obesity is, the higher the risk of Covid-19 complications.
- Being underweight is also linked to higher rates of hospitalisation and death.
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There's evidence that having a very high or very low body mass index (BMI) is a strong risk factor for more severe cases of Covid-19, according to a new report from the Centers for Disease Control and Prevention (CDC).
Research has previously suggested that obesity is linked to greater risk of Covid-19 complications. New data from the CDC supports this, and suggests being underweight could be dangerous, too.
CDC researchers studied data on 148,494 American adults who were hospitalised with Covid-19 from March to December 2020.
While age was the strongest risk factor, they found that coronavirus patients at either extreme of the body mass index (which measures height-to-weight ratio) were more likely to be hospitalised, require intensive care such as ventilation, or die of the disease than peers in the middle range of BMI.
While BMI is an imperfect measure of health, these findings suggest the relationship between Covid-19 risk and weight isn't straightforward. Instead, it seems to follow more of a J-curve. And people with the lowest risk are at the higher end of the "healthy" BMI range or just over the edge of an overweight BMI.
Consistent evidence links obesity to severe Covid-19
Obesity, defined as a BMI over 30, is linked to more severe Covid-19 cases, as well as a higher risk of complications, according to research.
Currently 42% of American adults have obesity, and people with obesity also make up the largest percentage of Covid-19 patients - slightly over half, in this latest CDC report.
The CDC report found that people with obesity were significantly more likely to be hospitalized, need intensive care, or die from coronavirus that other BMI ranges.
And the more severe the obesity, the greater the odds of Covid-19 complications. Those with severe obesity ranging from a BMI of 40 to more than 45 were among the highest-risk patients.
The risks are less certain for patients with an overweight BMI
The CDC report found an overweight BMI was a risk factor for requiring hospitalisation and intensive care.
In total, 78% of patients hospitalised for Covid-19 had a BMI in the overweight (or obesity) range, according to the report. That number seems startling, but it's proportional to the total number of Covid-19 patients in those categories.
In fact, people with an overweight BMI made up 28% of total patients in the report, but just 27.8% of hospitalizations, and 27.3% of deaths.
And some people in the overweight range were among the least likely to develop severe Covid-19. Having a BMI nearly or slightly over the overweight range was linked to the lowest overall risk of complications, the report found.
Being underweight could be just as risky, according to data
It's much less common for people to be underweight (having a BMI of less than 18.5) than to have obesity or overweight. Only 1.8% of the people in this latest CDC report were underweight.
But for coronavirus outcomes, low BMI was riskier than a high BMI. Underweight patients in the study had higher rates of hospitalisation and intensive care than people with obesity. And they were almost twice as likely to die of Covid-19 as people with obesity, even severe obesity, according to the report.
Being underweight was linked to a significantly higher than having BMI in the normal range, too. Patients who were underweight were 20% more likely to be hospitalized than their peers defined as normal weight. And the link between low BMI and risk was even stronger for Covid patients under 65 years old - younger people who were underweight were 40% more likely to be hospitalised for Covid-19 than their peers.
This could be explained at least in part due to underlying medical conditions, existing illnesses, or immune conditions associated with being underweight.