Obesity appears to be one of the biggest risk factors related to COVID-19 hospitalizations and critical illness, researchers have said. In a study of over 4,000 patients in New York City, scientists found that after age, obesity was one of the most significant factors associated with poorer health outcomes of coronavirus.

The research is pre-print, meaning it has not been peer reviewed by a panel of experts to evaluate the findings and published in a scientific journal. As a result, the findings should be taken with caution.

However, the results follow a number of warnings about how obesity may impact COVID-19 severity. Jean-François Delfraissy, who heads France's scientific council for coronavirus, told France Info radio: "Those who are overweight really need to be careful. That is why we're worried about our friends in America, where the problem of obesity is well known and where they will probably have the most problems because of obesity."

The U.S. Centers for Disease Control and Prevention currently lists people with extreme obesity—with a body mass index of 40 or over—as being at higher risk of severe illness from COVID-19.

In the latest study, led by Christopher Petrilli from the New York University Grossman School of Medicine, the team assessed various factors that were associated with critical illness and hospitalization. Of the 4,103 patients that had tested positive for COVID-19, they looked at different characteristics of each patient to identify the biggest risk factors among those who ended up with more severe outcomes.

Of the patients studied, 1,999 required hospital admission and 650 needed intensive care, were placed on a ventilator, died, or were discharged to hospice care.

Researchers found that age, by far, was the biggest risk factor for hospitalizations and critical care. After that, obesity, heart failure and chronic kidney disease were linked to more severe coronavirus cases.

"The risk factors we identified for hospitalization in COVID-19 are largely similar to those associated with any type of severe disease requiring hospitalization or ICU level care," they wrote.

However, the researchers added that what was "most striking" were the importance of inflammatory markers that appear to show which patients would need critical care. This, they say, could explain the risk posed by obesity.

"It is notable that the chronic condition with the strongest association with critical illness was obesity, with a substantially higher odds ratio than any cardiovascular or pulmonary disease," they wrote. "Obesity is well-recognized to be a pro-inflammatory condition."

The researchers note there are limitations to their work. For example, patients were all from New York and were treated in the same health system, so results may not be applicable to people in different parts of the U.S. and different countries. They also did not have information on inflammatory markers for people who were not hospitalized: "It is possible that these would have been strong predictors for hospitalization risk as well if available," they wrote.

Study author Leora Horwitz, from NYU Langone, told Newsweek they were surprised to see obesity was such a big factor in risk. "None of the initial reports from China examined obesity as a risk factor, so we didn't have existing evidence already showing it was important."

She explained that in severe cases of COVID-19, the body overreacts to the infection with inflammation, causing irritation to the lungs. "It turns out that obesity itself actually increases the amount of inflammation in the body. So it's possible that obesity also directly contributes to worse outcomes in that way."

Ian Hall, Director of the Centre for Biomolecular Sciences at the U.K.'s University of Nottingham, told Newsweek the study provides "a valuable analysis" of patients with COVID-19, showing obesity is a "major risk factor" in hospital admission.

He said that while obesity may be associated with other conditions placing the patient at greater risk, such as diabetes and heart failure, the researchers tried to control for this: "It looks as if obesity is by itself an independent risk factor for admission," he said.

Hall said one possible explanation is that people with severe obesity have lower oxygen levels than someone of a healthy weight. "Because having a low oxygen level is one of the main reasons for hospital admission this could result in more of the obese patients being admitted," he said. "However, there is a further possible explanation. It is well established that obesity is itself associated with an increased inflammatory response in the body, and so it is possible that the inflammatory response to SARS-CoV-2 infection may be increased in obese individuals when compared with individuals with a normal BMI."

"Whatever the explanation, given that in the U.S. and many other countries obesity is common it is useful for planning clinical care pathways to know that obesity appears to be an important independent risk factor for hospital admission," Hall said.

Joshua Bell, an epidemiologist at University of Bristol, U.K., said the results were "striking," but added they point to factors that mark poorer outcomes: "Not necessarily to factors which cause those poorer outcomes," he told Newsweek.

"This health threat is new, and it will take time to gather and link all the data needed to robustly identify factors which mark, and factors which cause, poorer outcomes. It would also be important to consider socioeconomic and occupational exposures in such studies.

"Obesity is a strong cause of diabetes and heart disease, largely through its effect on metabolic and inflammatory pathways. Knowing if any of those same pathways alter the course of COVID-19 may help reduce its impact and improve survival."

David Hamer, from the Boston University Schools of Public Health and Medicine, told Newsweek the findings mirrored preliminary findings from his own hospital. "It would not surprise me if subsequent studies show that this is a risk factor for COVID-19-related mortality," he said. "Given the 'growing' obesity epidemic in the US, this is definitely an association worth highlighting as obesity may increase both the severity of COVID-19 and potentially mortality."

The World Obesity Federation highlights a number of other issues relating to the hospitalization of obese patients. "Given the extremely high rates of obesity around the globe we expect that a high percentage of the population who will contract coronavirus will also have a BMI over 25," it said.

Problems treating obese people generally include not being able to intubate as easily, problems running diagnostic tests because of machine weight limits, and challenges moving them.

"Special beds and positioning/transport equipment are available in specialized surgery units, but may not be widely available elsewhere in hospitals and certainly not in all countries," World Obesity Federation said. "In general health systems are already not well set up to manage patients with obesity...and the current crisis will expose their limitations even more."

This article has been updated to include quotes from Leora Horwitz, Joshua Bell and David Hamer.

Centers for Disease Control and Prevention Advice on Using Face Coverings to Slow Spread of COVID-19

  • CDC recommends wearing a cloth face covering in public where social distancing measures are difficult to maintain.
  • A simple cloth face covering can help slow the spread of the virus by those infected and by those who do not exhibit symptoms.
  • Cloth face coverings can be fashioned from household items. Guides are offered by the CDC. (https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/diy-cloth-face-coverings.html)
  • Cloth face coverings should be washed regularly. A washing machine will suffice.
  • Practice safe removal of face coverings by not touching eyes, nose, and mouth, and wash hands immediately after removing the covering.

World Health Organization advice for avoiding spread of coronavirus disease (COVID-19)

Hygiene advice

  • Clean hands frequently with soap and water, or alcohol-based hand rub.
  • Wash hands after coughing or sneezing; when caring for the sick; before, during and after food preparation; before eating; after using the toilet; when hands are visibly dirty; and after handling animals or waste.
  • Maintain at least 1 meter (3 feet) distance from anyone who is coughing or sneezing.
  • Avoid touching your hands, nose and mouth. Do not spit in public.
  • Cover your mouth and nose with a tissue or bent elbow when coughing or sneezing. Discard the tissue immediately and clean your hands.

Medical advice

  • Avoid close contact with others if you have any symptoms.
  • Stay at home if you feel unwell, even with mild symptoms such as headache and runny nose, to avoid potential spread of the disease to medical facilities and other people.
  • If you develop serious symptoms (fever, cough, difficulty breathing) seek medical care early and contact local health authorities in advance.
  • Note any recent contact with others and travel details to provide to authorities who can trace and prevent spread of the disease.
  • Stay up to date on COVID-19 developments issued by health authorities and follow their guidance.

Mask and glove usage

  • Healthy individuals only need to wear a mask if taking care of a sick person.
  • Wear a mask if you are coughing or sneezing.
  • Masks are effective when used in combination with frequent hand cleaning.
  • Do not touch the mask while wearing it. Clean hands if you touch the mask.
  • Learn how to properly put on, remove and dispose of masks. Clean hands after disposing of the mask.
  • Do not reuse single-use masks.
  • Regularly washing bare hands is more effective against catching COVID-19 than wearing rubber gloves.
  • The COVID-19 virus can still be picked up on rubber gloves and transmitted by touching your face.