Does Sugar Really Suppress the Immune System?

Eating sugar may put your white blood cells into a temporary coma. But there’s a lot more to the story of how sugar affects our immune response.

Monica Reinagel, MS, LD/N, CNS
4-minute read
Episode #476

image of sugar pouring out of a soda can

As you may be aware, we are celebrating a Decade of Diva this year as the Nutrition Diva podcast approaches its tenth anniversary. You might think that after ten years of weekly podcasts, I’ve said just about everything that can be said about nutrition. No danger of that! Our understanding of how food affects our bodies is constantly expanding and evolving. Sometimes, that means modifying or even reversing our positions in light of newer evidence.

Case in point: when I started doing the Nutrition Diva podcast, calcium supplements were widely recommended to post-menopausal women as a hedge against osteoporosis. Since then, there’s been a steady drip of research suggesting that high-dose calcium supplementation after menopause does little to reduce the risk of bone fractures and may actually increase risk of other problems like kidney stones, colon polyps, and even heart attacks. High-dose calcium supplements are no longer the standard prescription. In fact, the US Preventive Services Task Force now recommends against calcium supplementation for most post-menopausal women.

That doesn’t mean that nothing can be done to strengthen your bones. For more on what you can do, see:

How Sugar Affects Immune Function

How sugar affects the body was another topic that I covered in the early years of the Nutrition Diva podcast. In 2010, I enumerated some of the ways that diets high in sugar can negatively impact your health. One of the things I mentioned was that sugar suppresses the immune system.

“When you eat a big dose of sugar like a bottle of Coke or a candy bar,” I wrote,  “you temporarily tamp down your immune system’s ability to respond to challenges. The effect lasts for several hours, so if you eat sweets several times a day, your immune system may be perpetually operating at a distinct disadvantage.” This widely held belief was based largely on research done in the 1970s in which study subjects donated blood before and after consuming a large dose of sugar. The blood was then placed in a petri dish and inoculated with a common strain of bacteria. Under a microscope, researchers could see that after a dose of sugar, certain white blood cells called neutrophils were far less aggressive in gobbling up the bacteria.

It was a vivid demonstration that served as a powerful cautionary tale about the harmful effects of sugar. But it’s striking that in the intervening 50 years, this study was never replicated or built upon. There is no research showing that consuming more sugar makes you more susceptible to colds or flu, for example.

But the immune response is a very complex system. Sending a neutrophil to gobble up an offending pathogen is just one of many different ways that the body defends itself.


About the Author

Monica Reinagel, MS, LD/N, CNS

Monica Reinagel is a board-certified licensed nutritionist, author, and the creator of one of iTunes' most highly ranked health and fitness podcasts. Her advice is regularly featured on the TODAY show, Dr. Oz, NPR, and in the nation's leading newspapers, magazines, and websites. Do you have a nutrition question? Call the Nutrition Diva listener line at 443-961-6206. Your question could be featured on the show.