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…