Why obesity increases the risk for severe COVID

In the United States, obesity rates have been increasing for decades. Nearly 42 percent—more than two in five—of adults have obesity, according to the Centers for Disease Control and Prevention (CDC). And 9.2 percent of U.S. adults have severe obesity, which is nearly twice the rate as about 25 years ago.

In the first year of the COVID pandemic, before vaccines became available, people with obesity made up more than 30 percent of COVID-related hospitalizations. And while being vaccinated has drastically lowered the number of people who are becoming severely ill, obesity continues to affect a person’s risk of having severe illness from the virus.

Several risk factors make it more likely a person could get severe symptoms from COVID. People older than 65, people from racial and ethnic minority groups, and those with disabilities are all at greater risk. The risk also increases with how many pre-existing medical conditions a person has. This includes conditions like diabetes, chronic lung disease, genetic conditions, congenital heart disease—and obesity.

What is obesity and what causes it?

By definition, obesity develops when people’s weight is greater than what is considered healthy for their height. Body mass index (BMI) is one measure used to help determine if someone is a healthy weight for their height. It’s calculated by dividing your weight in kilograms by your height in meters squared. (You can calculate your BMI here.)

Overweight and obesity are classified as the following:

• Overweight: BMI of 25 to less than 30
• Obesity: BMI of 30 or higher
• Class 1 obesity: BMI of 30 to less than 35
• Class 2 obesity: BMI of 35 to less than 40
• Class 3 obesity (severe obesity): BMI of 40 or higher

The obesity epidemic stems from many causes, such as where people live, their income and education level, other health conditions, stress, medications, genes, and health behaviors. This complexity means losing weight can be challenging.

Obesity is tied to severe COVID

Ongoing research is being carried out to more specifically pin down the reasons and mechanisms for why obesity raises the risk of severe COVID. But scientists have already learned a lot about this connection.

Obesity can contribute to severe COVID directly and indirectly. According to the CDC, obesity is linked to a weakened immune system and to lowered lung capacity (which can make breathing harder). Both of these issues can contribute to a more serious COVID infection. And indirectly, people with obesity are more likely to have chronic health issues, including heart disease and diabetes, which themselves raise the risk of severe COVID.

For some people, too much inflammation from an overactive immune system is a big reason for severe symptoms and long COVID. In extreme cases, the immune response can trigger what’s known as a cytokine storm, which is a life-threatening condition.

Young people are also at risk

While older age is a risk factor for more severe COVID infections, being obese can spell trouble for younger people, too. A November 2023 systematic review and meta-analysis published in Obesity Reviews looked at how overweight and obesity can affect a person’s risk of hospitalization from COVID. More than 2.3 million patients from 184 studies were divided into two groups: those younger than 50 and those who were 50 years or older.

Researchers found that for those younger than 50 years old, being overweight doubled the odds of hospitalization, and being obese tripled the odds. And for people older than 50, being obese almost quadrupled the odds of hospitalization.

Among U.S. adults between 20 and 39 years old, nearly 40 percent have obesity. Among adults between 40 and 59 years old, this percentage climbs to more than 44 percent.

And obesity can also raise children’s risk of severe COVID. Although children are overall much less likely to get severely ill, obesity may potentially triple their risk of hospitalization. Obesity affects 19.7 percent of U.S. young people between the ages of 2 and 19 , accounting for 14.7 million children, according to the CDC

Obesity and long COVID

A 2023 review published in Frontiers in Cardiovascular Medicine found that having obesity can also raise the risk of long COVID symptoms and of a longer recovery time overall. Researchers also found that having a higher BMI raised the risk of having clotting issues like deep vein thrombosis, pulmonary embolism, and maybe also micro-clots in small blood vessels that are hard to detect but can cause a range of health issues.

The reasons for the raised risk for long COVID are probably complex. One reason may be because adipose (fat) tissue can be a place where viruses linger even when they’ve cleared from the rest of the body. More research needs to be done to investigate their theory. And because obesity is already associated with lowered lung function, recovery may take longer because not enough oxygen gets to the areas of the body where it’s most needed.

Ways to protect your health

The number one way to prevent COVID infection is to get vaccinated against the virus, and to stay up to date on your vaccinations. COVID vaccines are the safest way to avoid being hospitalized or experiencing long-term health issues. Even if you’ve had COVID already, vaccines will offer added protection against being hospitalized from a re-infection.

However, several studies have revealed that people with obesity may not have as strong of an immune response to the vaccine, and the response may slow down much more quickly than people without obesity. If you have obesity, speak with your healthcare provider (HCP) about whether you may need more frequent booster shots.

Everyone ages 6 months and older can receive a COVID vaccine. Those younger than 5 years old and older than 65 may also need more than one dose of each updated vaccine.

The CDC also advises people with obesity to eat a healthy diet, engage in physical activity, get enough sleep, and try to cope with stress—all of which may help with weight loss and improve immune function.

For many, this is easier said than done. Losing weight and getting enough exercise may require lifestyle changes and developing some new habits. But incorporating some small, manageable healthy adjustments into your routine is a good start. Small steps can lead to bigger improvements over time.