Obesity and Increased Flu Risk

Flu season is upon us, and you may be preparing by getting a flu shot, washing your hands frequently, and stocking up on disinfectant. But it might surprise you to learn that being overweight can worsen complications from the flu.

Those extra pounds put all the body’s systems under more strain, and that weakens its ability to defend against infection. One source of strain is excessive inflammation. Inflammation is the body’s response to attack or injury. We experience it as redness and swelling that appears around a cut, or the stuffy nose or headache that heralds a cold. It can also happen internally, where we can’t see or feel it. It’s caused by swarms of immune cells converging on the site of injury or infection. In short bursts, inflammation helps maintain a healthy body, as the immune system defends against infection and cleans up debris from damaged cells.

Being overweight, however, causes low-grade chronic inflammation throughout the body. This ongoing state of inflammation disrupts the usual processes by which our bodies fight off microscopic invaders, like the flu virus. When cells want to communicate with each other, they release molecules called cytokines, tiny particles that transmit chemical signals to other cells. One important job of the cytokines is managing inflammation.

A cytokine called adiponectin puts the brakes on the cellular mechanisms that cause inflammation. A different one, leptin, hits the gas pedal. They, and others, help keep inflammation confined to where and when it’s needed. Researchers have found that being overweight throws these signal molecules out of whack, reducing the amount of adiponectin and increasing leptin. This leads to out of control inflammation throughout the body. Under those conditions, the immune system becomes less effective at ridding the body of the flu virus.

This chronic inflammation may not be something you feel or notice in everyday life, but it has measurable health consequences. Several studies have investigated how obesity affects the severity of the flu. It turns out that people with a body mass index (BMI) of 30 or higher were more likely to be hospitalized with respiratory complications during flu season, and have longer hospital stays, than people whose BMI fell within the normal range.

But what about flu shots? Surely getting vaccinated bolsters the immune system against the onslaught of flu virus. It definitely does! A vaccine works by spurring the body to make antibodies against the flu virus, so that you’re armed and ready to eliminate the virus when you encounter it in your daily interactions. A recent study found that people who are overweight respond well to the vaccine — at first. Higher BMI was correlated with more vigorous antibody production in the first weeks following the injection. However, by 12 months post-vaccine, the overweight individuals had lost more of their immunity to the virus than those considered healthy weight.

Maybe you’re thinking to yourself, I’ll take my chances. You may have made it through past flu seasons without serious complications. Well, it turns out, being overweight could make it riskier for people to be around you. How is that possible? A research study published last year discovered that obese adults who get the flu continue to shed the virus up to 42% longer than their lean counterparts. This increases the likelihood that those around them will come into contact with the virus.

This flu season, as you make your preparations for the annual onslaught of disease, consider how healthy weight loss could improve your ability to stay flu-free and protect the ones you love.


Rojas-Osornio SA, et al. Immunity to influenza: Impact of obesity Obesity Research & Clinical Practice, published online 19 Sept 2019

Maier HE, et al. Obesity Increases the Duration of Influenza A Virus Shedding in AdultsThe Journal of Infectious Diseases, 2018; 218 (9): 1378–1382.


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