The coronavirus has been an unpredictable foe from the start. It triggers silent or barely perceptible infections in some individuals, while in others it sets off a cascade of complications that overwhelm the body and lead to death.
Why some patients sail through the disease and others are felled by it is a question that has bedeviled doctors.
Older age and chronic health conditions like high blood pressure and heart disease are known to increase the risk of severe Covid-19. The Centers for Disease Control and Prevention also lists extreme obesity as a high risk.
But is excess weight in and of itself to blame? Or all of the health problems that accompany obesity, like metabolic disorders and breathing problems?
A new study points to obesity itself as a culprit. An analysis of thousands of patients treated at a Southern California health system identified extreme obesity as an independent risk factor for dying among Covid-19 patients — most strikingly, among younger and middle-aged adults 60 and younger, and particularly among men.
Among women with the illness, body mass index — a measure of body fat based on height and weight — does not appear to be independently associated with an increased risk of dying at any age, the authors said, possibly because women carry weight differently than do men, who tend to have more visceral and abdominal fat. The study was published in Annals of Internal Medicine on Wednesday.
“Body mass index is a really important, strong independent risk factor for death among those who are diagnosed with Covid-19,” said Sara Tartof, the study’s first author, a research scientist at Kaiser Permanente of Southern California.
But “the impact is not uniform across the population,” she added. “You don’t really see it for the older ages, and we didn’t see it as an important risk for females at any age.”
Obesity and the coronavirus are a dangerous combination for a number of reasons.
Obesity causes restricted breathing, making it more difficult to clear pneumonia and other respiratory infections. Fat is biologically active and a source of pro-inflammatory chemicals, promoting a state of chronic inflammation in the body even before Covid-19 sets in. Obesity causes metabolic changes and abnormalities, even in the absence of diabetes.
The study is not the first to finger obesity as a culprit in Covid-19 deaths in younger people. While early reports from China and Italy did not focus on obesity as an independent risk factor, physicians in other parts of the world, where obesity is more prevalent, were quick to notice that younger individuals who became very ill were often obese.
Only 6 percent of the Chinese population is obese, compared with 20 percent of the population in Italy and 24 percent in Spain. The United States, by contrast, has one of the highest rates of obesity in the world.
Some 42 percent of American adults have a body mass index of 30 or more, which classifies them as having obesity, and 9 percent have a B.M.I. of 40 or more. (Someone who is 5’9’’ tall and weighs 270 pounds or more has a BMI of 40, according to federal guidelines.) An individual of that height at 304 pounds has a B.M.I. of 45.
Normal weight ranges from a B.M.I. of 18.5 to 24.9; people with B.M.I.s of 25 to 29.9 are considered overweight.
A report issued by Public Health England concluded that being overweight or obese increased the risk of complications and death from Covid-19. Hundreds of similar articles on the topic have been published.
Among them was a study last month from Columbia University, also published in Annals of Internal Medicine, which found that individuals with Covid-19 who were extremely obese were 60 percent more likely to require mechanical ventilation or to die from Covid-19. The study noted that this was also the case for people under age 65.
“Is it just that we in the United States have more obese people, so we’re seeing this?” said Dr. David Kass, a professor of medicine at Johns Hopkins University who wrote an editorial accompanying the new study.
“But this is beyond the proportion that would just be in the general population,” he said. “It’s not just that there are a lot of fat people, so we’re seeing a lot of fat people who are very sick.”
Dr. Kass wrote a letter in the Lancet in April noting that many younger Covid-19 patients admitted to American hospitals suffered from obesity, and predicting that as the coronavirus spread through areas where obesity was more prevalent, more younger people would be affected.
The disparate effect on men who are obese is also understandable, he said, because of differences in fat distribution. “If you take a man and woman side by side with the same B.M.I., the male is much more likely to have the background problems that we think are a component for being more at risk,” Dr. Kass said.
To carry out the new study, researchers analyzed the health records of 6,916 members of the Kaiser Permanente Southern California Health System who were treated for Covid-19, both as inpatients and outpatients, from mid-February to May 2.
The median age of the patients was 49 years, and the mean B.M.I. of the patients was 30.6; nearly half were obese.
The Coronavirus Outbreak ›
Frequently Asked Questions
Updated August 12, 2020
Can I travel within the United States?
- Many states have travel restrictions, and lots of them are taking active measures to enforce those restrictions, like issuing fines or asking visitors to quarantine for 14 days. Here’s an ever-updating list of statewide restrictions. In general, travel does increase your chance of getting and spreading the virus, as you are bound to encounter more people than if you remained at your house in your own “pod.” “Staying home is the best way to protect yourself and others from Covid-19,” the C.D.C. says. If you do travel, though, take precautions. If you can, drive. If you have to fly, be careful about picking your airline. But know that airlines are taking real steps to keep planes clean and limit your risk.
I have antibodies. Am I now immune?
- As of right now, that seems likely, for at least several months. There have been frightening accounts of people suffering what seems to be a second bout of Covid-19. But experts say these patients may have a drawn-out course of infection, with the virus taking a slow toll weeks to months after initial exposure. People infected with the coronavirus typically produce immune molecules called antibodies, which are protective proteins made in response to an infection. These antibodies may last in the body only two to three months, which may seem worrisome, but that’s perfectly normal after an acute infection subsides, said Dr. Michael Mina, an immunologist at Harvard University. It may be possible to get the coronavirus again, but it’s highly unlikely that it would be possible in a short window of time from initial infection or make people sicker the second time.
I’m a small-business owner. Can I get relief?
- The stimulus bills enacted in March offer help for the millions of American small businesses. Those eligible for aid are businesses and nonprofit organizations with fewer than 500 workers, including sole proprietorships, independent contractors and freelancers. Some larger companies in some industries are also eligible. The help being offered, which is being managed by the Small Business Administration, includes the Paycheck Protection Program and the Economic Injury Disaster Loan program. But lots of folks have not yet seen payouts. Even those who have received help are confused: The rules are draconian, and some are stuck sitting on money they don’t know how to use. Many small-business owners are getting less than they expected or not hearing anything at all.
What are my rights if I am worried about going back to work?
- Employers have to provide a safe workplace with policies that protect everyone equally. And if one of your co-workers tests positive for the coronavirus, the C.D.C. has said that employers should tell their employees — without giving you the sick employee’s name — that they may have been exposed to the virus.
What is school going to look like in September?
- It is unlikely that many schools will return to a normal schedule this fall, requiring the grind of online learning, makeshift child care and stunted workdays to continue. California’s two largest public school districts — Los Angeles and San Diego — said on July 13, that instruction will be remote-only in the fall, citing concerns that surging coronavirus infections in their areas pose too dire a risk for students and teachers. Together, the two districts enroll some 825,000 students. They are the largest in the country so far to abandon plans for even a partial physical return to classrooms when they reopen in August. For other districts, the solution won’t be an all-or-nothing approach. Many systems, including the nation’s largest, New York City, are devising hybrid plans that involve spending some days in classrooms and other days online. There’s no national policy on this yet, so check with your municipal school system regularly to see what is happening in your community.
In general, obesity rates vary by race and ethnicity, according to the C.D.C. The age-adjusted obesity rate among Blacks is 49.6 percent, compared with 45 percent among Hispanics, 42 percent among whites and 17 percent among Asian-Americans.
Just over half of the Kaiser Permanente patients were Hispanic, about 1,000 were Asian/Asian-American, and 584 were Black. Many patients had underlying health problems that are linked to poor Covid-19 outcomes. Some 206 — or 3 percent — of the patients died within 21 days of receiving a Covid-19 diagnosis.
To figure out whether obesity, in and of itself, was associated with a higher death risk, the researchers tried to factor out conditions like high blood pressure and diabetes, which are known to be associated with more severe forms of Covid-19, as well as heart, kidney and chronic lung disease.
The scientists also wanted to know whether demographic factors, like age, sex and race or ethnicity, played a role.
While Black and Latino populations have been disproportionately stricken by the virus, with hospitalizations and deaths at higher rates, the study did not find race or ethnicity to be an independent risk factor.
The researchers did find extreme obesity to be a strong independent risk factor for worse outcomes. “We’re not saying the disparities don’t exist — we’re teasing apart what’s driving the disparities,” Dr. Tartof said.
“We see that racial and ethnic minorities are having more bad outcomes. They are also more likely to be obese, or to have less access to health care, and they’re more likely to have co-morbidities.”
Among Covid-19 patients in the study, those with extreme obesity — defined as a B.M.I. of 40 or more — were at nearly three times greater risk of dying than those of normal weight. Those with a B.M.I. of 45 were more than four times more likely to die than patients of normal weight, with the risk most striking among men and those under 60, Dr. Tartof said.
The study draws attention to the intersection of two major health concerns, Dr. Tartof said, underscoring the need for policies to tackle both.
“There is a lot of work we can do to better combat Covid, and a lot we can do to improve our strategies on obesity as well,” she said. “It is also an epidemic, and something we need to pay attention to.”