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Added Sugars Negatively Impact Immune System

Most Americans exceed recommendations for sugar intake

by Whitney Crouch, RDN, CLT

Sugar is a hot topic. It’s one of the recently recognized, major culprits for increasing rates of overweight and obesity, type 2 diabetes, and heart disease and contributes to a multitude of other health conditions related to inflammation in the body.1

Sugar intake in America

42% of Americans ≥ 2 years meet the 2015-2020 Dietary Guidelines for Americans recommendation for limiting added sugars intake to <10% of daily calories.1-2 That leaves 58% of Americans consuming >10% of daily calories from added sugars, and the actual amount of sugar consumed by these individuals is staggering.

On average, those who met the Dietary Guidelines recommendation consumed almost 7 teaspoons of added sugars daily, and those who did not consumed about 25 teaspoons of added sugars/day (1 tsp of added sugar = 4.2 grams of sugar),1 which is about 420 calories/day from added sugars alone.

Examples of added sugars include brown sugar, corn sweetener, corn syrup, dextrose, fructose, glucose, high-fructose corn syrup, honey, lactose, malt syrup, maltose, molasses, raw sugar, and sucrose.2

Excessive sugar intake: long-term consequences

Sugar is thought to be a pro-inflammatory agent in the body. When blood sugar levels are elevated for extended periods of time, the body may be placed into an inflammatory state, which can lead to cellular dysfunction and changes to both the innate and adaptive immune systems. It is postulated that elevated sugar intake produces elevated free fatty acid production by the liver, which may trigger the inflammatory process and increase reactive oxidative species (ROS) formation.3

The innate immune system represents the dominant defense system against most organisms; it has a fast response to infection but no immunological memory.4 In contrast, the adaptive immune system has immunological memory that promotes quick elimination of pathogens when reinfection with the same pathogen occurs. It includes T and B lymphocytes and antibodies.5

Obesity, physical inactivity, and consumption of excess refined sugars have been associated with an increased risk of type 2 diabetes, as well as autoimmune and inflammatory diseases.6,7 Obese individuals have fewer white blood cells to fight infections, and the cells they do possess have reduced phagocytic capability.8 Sustained hyperglycemia, such as in diabetes, is associated with an elevated risk of autoimmune and inflammatory diseases (i.e., rheumatoid arthritis, asthma, psoriasis), as well as cancer.9

Excessive sugar intake: short-term consequences

The link between excess body weight, type 2 diabetes, tooth decay, and heart disease from overconsumption of sugar are well established.5 But what does too much sugar do to the fast-acting, innate immune system? Studies have looked at what happens in the blood after consumption of large amounts of sugar, and in short, depressing effects on the innate immune system were seen.10,12

One such study looked at the blood after healthy study participants consumed 100 g (25 teaspoons) of sucrose, glucose, or fructose.10 As a result of the high sugar intake (which also happens to be the average intake of added sugars in 58% of Americans), there was a transient 50% decrease in neutrophils’ capacity to engulf bacteria in the 1-2 hours after the sugary drink was consumed.10 Neutrophils are the most common type of white blood cell (WBC), comprising 55-70% of the WBC count, and are responsible for immediate responses to infection or attacks on the body’s cells.11

Another study looked at the phagocytic capacity of neutrophils in healthy students who either ingested a sugar-containing or sugar-free beverage. No neutrophil abnormalities were found after drinking the sugar-free drink, however there was a significant decrease in the mean phagocytic (ability to engulf pathogens) index after in the group ingesting the sugar-containing drink.12

Together, these studies shine light on the body’s impaired ability to fight off bacterial invaders when high sugar drinks are consumed – a trend that is prevalent in the Standard American Diets.1

The leading sources of added sugars in the US diet are sugar-sweetened beverages, grain-based desserts like cakes and cookies, candy, and dairy desserts such as ice cream.13 For reference, one 16-oz bottle of Coca-Cola contains 52 g of added sugar (or ~13 tsp of added sugar).14

Sugar intake and your health

Added sugars are ubiquitous in processed foods. To limit intake of sugar to achieve the recommended <10% of daily calories, the Office of Disease Prevention and Health Promotion (ODPHP) recommends a diet rich in a variety of vegetables (starchy and non-starchy), whole fruits, quality proteins, and grains if tolerated.1

In addition to dietary awareness, maintaining regular exercise helps support healthy blood glucose levels. Exercise is the most potent physiological inducer of efficient glucose storage and reduces the severity of hyperglycemic events, in addition to the risk and severity of autoimmune diseases.9 Muscular uptake of blood glucose helps to regulate circulating blood post-prandial blood sugars, and the greater the muscle mass, the greater the uptake of blood sugars.15

Healthcare providers would be wise to assess intake of added sugars in the diet of their patients and partner to provide recommendations and implementation tools for their patients to achieve healthful, nutrient-dense dietary patterns that suit their personal health needs and preferences.


  1. Bowman SA et al. Added sugars intake of Americans: What we eat in America, NHANES 2013-2014. Food Surveys Research Group. Dietary Data Brief No. 18. May 2017.
  2. USDHHS and USDA. Added sugars. 2015–2020 Dietary Guidelines for Americans. Accessed November 29, 2018.
  3. Della Corte KW et al. Effect of dietary sugar intake on biomarkers of subclinical inflammation: a systematic review and meta-analysis of intervention studies. Nutrients. 2018;10(5):606.
  4. Inweregbu K et al. Nosocomial infections. Contin Educ Anaesth Crit Care Pain. 2005;5(1):14–17.
  5. Janeway CA Jr et al. Immunobiology: The Immune System in Health and Disease: Principles of Innate and Adaptive Immunity. 5th ed. New York:2001.
  6. Malik VS et al. Sugar-sweetened beverages, obesity, type 2 diabetes mellitus, and cardiovascular disease risk. Circulation. 2010;121(11):1356-1364.
  7. Gaby A. A review of the fundamentals of diet. Glob Adv Health Med. 2013;2(1):58-63.
  8. Nieman DC et al. Influence of obesity on immune function. J Am Diet Assoc. 1999;99(3):294–299.
  9. Hansen NW et al. The endothelial border to health: Mechanistic evidence of the hyperglycemic culprit of inflammatory disease acceleration. IUBMB Life. 2017;69(3)L148–L161.
  10. Sanchez A et al. Role of sugars in human neutrophilic phagocytosis. Am J Clin Nutr. 1973;26:1180–1184.
  11. American Society of Hematology. Blood Basics. Accessed November 16, 2018.
  12. Ringsdorf WM Jr et al. Sucrose, neutrophilic phagocytosis and resistance to disease. Dental Survey.1976;52:46-48.
  13. Drewnowski A et al. Consumption of added sugars among US children and adults by food purchase location and food source. Am J Clin Nutr. 2014;100(3):901-907.
  14. How Much Sugar In Coke Is There? | Product Facts. Accessed November 16, 2018.
  15. Sylow L et al. Exercise-stimulated glucose uptake – regulation and implications for glycaemic control. Nat Rev Endocrinol. 2017;13(3):133-148.


Whitney Crouch, RDN, CLT 

Whitney Crouch is a Registered Dietitian who received her undergraduate degree in Clinical Nutrition from the University of California, Davis. She has over 10 years of experience across multiple areas of dietetics, specializing in integrative and functional nutrition and food sensitivities. When she’s not writing about nutrition or educating others, she’s spending time with her husband and young son. She’s often found running around the bay near her home with the family’s dog or in the kitchen cooking up new ideas to help her picky eater expand his palate.


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