Every winter like clockwork, temperatures start to drop and the flu starts to spread — and this year's flu season is no different. Between October 1 and November 30 alone, preliminary data from the Centers for Disease Control and Prevention (CDC) shows that the flu has been responsible for up to 29,000 hospitalizations and as many as 2,400 deaths.
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While some factors like age and illness determine who gets the flu and how serious the infection may be, what many people don't know is that weight plays a role in developing the flu as well, and in more than one way. Here's how.
1. Depending on Your Weight, You Might Be More Susceptible
Health care professionals have known for years that certain populations — such as the elderly and immunocompromised — are at an increased risk for developing the flu, per the CDC. But in 2011, a landmark study revealed for the first time that adults who had overweight or obesity were also an especially vulnerable population.
The study, published in the February 2011 issue of Clinical Infectious Disease, revealed that among residents in California during the 2009 H1N1 flu outbreak, the vast majority of hospitalized patients had overweight or obesity with a body mass index (BMI) of 30 or above.
And another study, from the December 2017 issue of the International Journal of Obesity, revealed that people with a high BMI have twice the likelihood of developing the flu compared to those at a healthy weight — even after they received a flu shot.
Researchers aren't completely sure why a higher-than-healthy weight might contribute to getting the flu, but Stacey Schultz-Cherry, PhD, a professor of infectious diseases at St. Jude Children's Research Hospital in Memphis, Tennessee, says it might come down to a delayed immune response.
"The flu virus enters through the nose and upper respiratory tract first," says Schultz-Cherry. "Our cells then make very potent antiviral and anti-pathogen responses that need to come on quickly to help fight the infection."
But Schultz-Cherry's current research, which studies the effect of the flu virus on our cells, suggests that cells found in the lungs of people with obesity might not react as quickly as those in lower-BMI populations. "The cells aren't recognizing that there's a virus there," Schultz-Cherry says, which delays the other immune responses necessary for clearing the infection and repairing the lungs.
Read more: 5 Uncommon Ways to Fend Off Cold and Flu
2. You Might Be More Contagious
Not only are you more likely to get the flu if you have overweight, but you may also end up spreading it around to more people.
In November 2018, a study published in the Journal of Infectious Diseases showed that age and obesity were both associated with how long a patient "shed" the virus, allowing it to be transmitted to other people. Adults with obesity, the study said, shed the influenza A virus 42 percent longer than those at a healthy weight, with a mean shedding time of five days compared to three.
"What studies have shown is that people with obesity might be exhaling more of the virus than those without the condition," Schultz-Cherry says. "People are shedding the virus for longer periods of time, but they also have more of the virus that they're actually shedding."
3. If Your BMI Is High, Your Risk of Flu Complications Is Too
Though influenza is potentially serious no matter who gets it, people who have overweight or obesity have a higher likelihood of suffering life-threatening complications, according to the American Lung Association.
Studies support this as well: A January 2019 study in the journal Influenza and Other Respiratory Viruses showed that in a study of six hospitals across Mexico, adults with obesity were six times more likely than healthy-weight individuals to be admitted to the hospital due to flu complications.
"We're not sure if it's obesity per se," Schultz-Cherry says. "We think the flu risk might have more to do with a metabolic syndrome or an underlying condition that causes you to be immunocompromised."
At the same time, says Schultz-Cherry, people who have overweight and obesity tend to have chronic, low-level inflammation that can impede the immune system. More research is needed, says Schultz-Cherry, to determine exactly why obesity seems to make the flu so much worse. But similar to how a suppressed immune system makes it more likely to catch the flu, it also increases the severity of the symptoms.
And, Schultz-Cherry says, as a person's BMI climbs, the risks associated with the flu climb as well. People with BMIs of 40 and above have the highest chance of developing complications from the flu, according to the CDC, including death.
How to Protect Yourself
All this talk about higher flu risk and complications may be worrisome, but there are still things you can do to boost your immune system and stay healthy.
1. Wash your hands with soap and water often. It may sound simple, but this small act is still one of the best ways to prevent catching the flu, says Schultz-Cherry. Just make sure you're getting a good scrub: Sing the "Happy Birthday" song twice through as you wash your hands to make sure you're cleansing them thoroughly.
In addition, try to avoid touching your eyes, nose or mouth, since flu germs can easily enter your body this way, per the CDC.
2. Get a flu shot. No, it's not foolproof, admits Schultz-Cherry. But it's still one of the most important steps you can take to protect yourself. "The flu shot may not work as well as we would like it to, but it may still protect against complications like heart attack, stroke or dying, and that's crucial for a high-risk population," she says.
The CDC recommends getting your shot before the end of October, but if you missed that window, you can still benefit from getting the shot anytime during flu season.
3. Prioritize sleep. Getting less than the recommended seven to eight hours a night may decrease your immune function, leaving you more vulnerable to the flu, according to the National Sleep Foundation. Make catching good zzzs a must by scheduling it in like any other daily activity.
4. Eat foods that support your immune system. A diet full of nourishing nutrients is a key way to keep your immune system in tip-top shape. Check out five foods that can help your body fight back against infections like the flu.
5. Get moving. Aerobic exercise like walking, jogging or swimming activates your immune system, per the Mayo Clinic. Getting in regular physical activity may leave you less susceptible to viral illnesses. Just make sure you're taking healthy precautions at the gym.
6. If you do get sick, ask your doctor about antiviral drugs. These prescription meds may help shorten your illness and prevent serious flu complications, according to the CDC. Studies show these drugs work best when started within 48 hours of getting sick, but starting them later can still be helpful for people with higher-risk conditions.
- CDC: "2019-2020 U.S. Flu Season: Preliminary Burden Estimates"
- CDC: "People at High Risk for Flu Complications"
- American Lung Association: "Flu Symptoms, Causes, and Risk Factors"
- Clinical Infectious Diseases: "A novel risk factor for a novel virus: obesity and 2009 pandemic influenza A (H1N1)."
- International Journal of Obesity: "Increased risk of influenza among vaccinated adults who are obese"
- The Journal of Infectious Diseases: "Obesity Increases the Duration of Influenza A Virus Shedding in Adults"
- Influenza and Other Respiratory Viruses: "Underweight, overweight, and obesity as independent risk factors for hospitalization in adults and children from influenza and other respiratory viruses"
- CDC: "Frequently Asked Flu Questions 2018-2019 Influenza Season"
- CDC: "Healthy Habits to Help Prevent Flu"
- CDC: "Influenza (Flu): Preventive Steps"
- National Sleep Foundation: "Sleep May Be Best Prevention for Cold, Flu"
- Mayo Clinic: "Aerobic exercise: Top 10 reasons to get physical"