Doctors warn that sugar can temporarily weaken your immune system

You may have another reason to kick that soda habit for good.

Mercey Livingston CNET Contributor
Mercey Livingston is a health and wellness writer and certified Integrative Nutrition Health Coach. She's written about fitness and wellness for Well+Good, Women's Health, Business Insider, and Prevention.com among others. When not writing, she enjoys reading and trying out workout classes all over New York City.
Mercey Livingston
3 min read

Sugar can temporarily weaken your immune system -- here's how that happens.

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Doing everything you can to keep your immune system strong can feel like a lot of work. Committing to an exercise routine, good sleep habits, taking supplements, stress management and good nutrition is no small feat, but well worth your time and effort when it comes to staying well. But what if all your valiant efforts could be undone (for about five hours) just by eating one certain food?

If your sweet tooth has emerged with a vengeance during stay-at-home orders and quarantine, then listen up: according to nutrition studies and health experts, you might want to rethink your sugar habit. "Too much sugar in your system allows the bacteria or viruses to propagate much more because your initial innate system doesn't work as well. That's why diabetics, for example, have more infections," Dr. Michael Roizen, MD and COO of the Cleveland Clinic told CNET

Keep reading below to find out exactly how sugar affects your immune system, what science has to say on the subject and how much sugar it takes to create the negative effects.

Read more: 8 ways eating too much sugar is bad for your health


Donuts and cupcakes are tempting treats but often contain more sugar than you should get each day.

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How does sugar affect your immune system? 

Besides being a driver behind other chronic health conditions like diabetes and heart disease, sugar consumption affects your body's ability to fight off viruses or other infections in the body. You know how your body needs certain cells to fight off infections? White blood cells, also known as "killer cells," are highly affected by sugar consumption. Like Dr. Roizen mentions, sugar hinders the immune system since, according to a study done on fruit flies, the white blood cells are not able to do their job and destroy bad bacteria or viruses as well as when someone does not eat sugar.

Another study showed that high blood sugar affects infection-fighting mechanisms in diabetics. High-sugar diets are linked to Type 2 diabetes since high sugar consumption can lead to diabetes -- a condition that in particular is associated with a higher risk of serious complications from COVID-19. 

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How much sugar does it take to weaken your immune response

This nutrition study shows that it takes about 75 grams of sugar to weaken the immune system. And once the white blood cells are affected, it's thought that the immune system is lowered for about 5 hours after. This means that even someone who slept 8 hours, takes supplements and exercises can seriously damage their immune system function by drinking a few sodas or having candy or sugary desserts throughout the day. 

That study above was published in the 1970s, but another study from 2011 expanded on the previous research and found that sugar, especially fructose (like the sugar in high-fructose corn syrup) negatively affected the immune response to viruses and bacteria.

Just to give you context of how 75 grams of sugar can add up:

  • One can of soda has about 40 grams of sugar
  • A low-fat, sweetened yogurt can have 47 grams of sugar
  • A cupcake has about 46 grams of sugar
  • Sports drinks can contain about 35 grams of sugar

Health authorities say to limit sugar to no more than 6 teaspoons a day.

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How much sugar is considered healthy to eat in a day?

The US Office of Disease Prevention and the World Health Organization recommend that you should get no more than 10% of your daily calories from added sugar each day. Another way to look at that amount is to limit your sugar intake to no more than six teaspoons, or 25 grams total. This amount includes the sugar you may add to your coffee, the sugar in your daily chocolate serving or the hidden sugars often found in "healthy" foods like granola bars or smoothies. 

Finally, if you stick to a well-balanced diet and keep your sugar consumption in check (ideally limit it to 25 grams a day), then your immune system will have a better chance to do its job and keep you from getting sick. Now is not the time to go crazy with baking desserts (no matter how much you want to perfect that cake or cookie recipe!). Enjoying them from time to time is fine, but moderation is key when it comes to staying well. 

Watch this: Driscoll's: The food supply chain is much more fragile than any of us thought
The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.