One of the easiest strategies to preserve immune function is to avoid refined sugar. Sugar has a significant disabling effect on our immune system which means, if you’re consuming it, you are more at risk of picking up what’s going around – and less able to fight something off should you catch it.

In a nutshell, sugar has a negative impact on our immunity due to it’s similarity in structure to vitamin C which – when taken up instead of vitamin C – renders white blood cells (WBCs) vulnerable. Let me explain that in a bit more detail.

Sugar Blocks Vitamin C

In order to get why this is such a big deal it is important to understand the role of Vitamin C in healthy immune function and the way our body uses it, and therefore how detrimental it is when sugar affects this.

Firstly, WBCs (especially phagocytes and t-cells) accumulate 50-80 times more Vitamin C than the blood they’re carried in – and for very good reason.

In order to destroy germs, our WBCs produce highly toxic free radicals with which to destroy these bugs. To be more specific – in response to invading microorganisms (i.e. bacteria or viruses), phagocytic* WBCs actually release non-specific toxins, such as superoxide radicals, hypochlorous acid (‘bleach’), and peroxynitrite; these reactive oxygen species kill microorganisms but, in the process, can damage the WBCs themselves[1].

The accumulation of vitamin C to extremely high concentrations  is in order to protect themselves from the oxidative damage these toxins can do[2,3,4]  – and Vitamin C, through its antioxidant functions, has been shown to protect WBCs from this self-inflicted oxidative damage[5].  Vitamin C levels rapidly decline during infections and stress as the WBC uses vitamin C to protect itself![6]

Phagocytosis* is the process by which our WBCs consume and neutralise pathogens (microorganisms that can make us sick) – this is basically gobbling up bad bugs and destroying them in the process, a bit like Pacman – and they have to constantly be accumulating Vitamin C to maintain a high concentration of vitamin C, and thus it’s phagocytic capabilities (called the phagocytic index)!

The Phagocytic Index

So what exactly is the phagocytic index?

The phagocytic index is a measure of phagocytic activity determined by counting the number of bacteria ingested per phagocyte (WBC) during a limited period of incubation of a suspension of bacteria and phagocytes in serum.

Basically, when you put WBCs in the same ‘petri dish’ as bacteria you can measure either how quickly they gobble up the bacteria/the rate at which the bacteria are removed from the ‘petri dish’.

The consumption of sugar results in the WBCs preferentially taking up sugar instead of vitamin C, and specifically reduces the phagocytic index – reducing the ability of the WBC to mop up bad bugs.

Sugar has a very similar molecular structure to vitamin C and, when we consume sugar, it directly competes with vitamin C and – as a result – less vitamin C enters into WBCs. Sugar does not help WBCs to fight against germs and thus reduces the WBCs ability to deal with invading microorganisms[7].

Given that vitamin C places a number of critical roles in WBC protection and function, it is now clear why when WBCs take up sugar instead, it suffers.

So How Much Sugar Is Too Much

Glucose is a carbohydrate whose level in blood changes throughout the day and, when glucose levels fluctuate, WBCs are affected. It is not yet known if there is a safe level of sugar intake, and what that is. However we do know at what level it is most definitely a problem.

A study[8] that looked to determine whether carbohydrates other than glucose decreased the phagocytic index (PI), also looked at how long this effect lasted:

• Oral 100-g portions of carbohydrate from glucose, fructose, sucrose, honey, or orange juice all rapidly and significantly decreased the PI
• Typically WBCs can consume about 16 bacteria in a fasting state, but 2 hours after sugar ingestion, they could only consume 9-10 bacteria
  • Suppression of activity occurred as quickly as 30 minutes
  • The greatest effects occurred in the first 1-2 hours
    • Fructose was the worst (reducing phagocytosis by 45%) but all other sugars still suppressed activity by more than 40%
  • Effects lasted for at least 5 hours and it took about 5-6 hours for vitamin C levels to return to original concentration
• Starch ingestion did not have this effect, reducing the PI by just 13%
• Interestingly, a fast of 36 or 60 hr significantly increased the PI (perhaps the loss of appetite when we’re unwell is to support the immune system as well as prevent energy and circulation being diverted to digestion?)

It is important to keep in mind what a 100g portion looks like. It is unlikely someone would (or could) consume 100g of honey in one sitting, but 100g of orange juice (roughly 100ml) is easy to consume. I’m sure no-one can imagine consuming 100g table sugar (25 teaspoons) and yet – consuming a bottle of soft drink and a regular muffin will produce the same result. Of course a bag of sweets will take you way over 100g but even a large bowl of commercial cereal with low-fat milk will also get you close!

You can see how easy it would be to operate all day with an impaired immune system and why it’s critical for immunity that you avoid refined sugar – especially during cold and flu season.

The PI is also important as it relates to cancer and this study[9] showed that:

• high intakes of sugar and refined carbohydrates, and elevated blood glucose, are strongly associated with the risk of cancer
• high carbohydrate intake is associated with poorer survival after diagnosis for early breast cancer
• high blood sugar can impair the actions of vitamin C, damage immune effectiveness and hinder cancer survival
• a statistically significant lower average blood glucose was found in those in remission

Vitamin C Boosts Immunity

In addition to the Phagocytic Index, vitamin C helps support our immune system to do it’s job in other ways too:

• Vitamin C has been shown to stimulate the production of white blood cells[10,11,12,13,14]
• Vitamin C has been shown to stimulate the function of white blood cells[15,16]
• Vitamin C has been found to improve components of the human immune system such as antimicrobial and natural killer cell activities and lymphocyte proliferation[17]
• Specific measures of functions stimulated by vitamin C include
  • cellular motility[18] (how spontaneously and actively the WBCs move)
  • chemotaxis[19,20]  (how well the WBCs move in response to pathogens i.e. towards them)
  • phagocytosis

Phagocytic WBCs also produce and release cytokines, including interferons, which have antiviral activity and vitamin C has been shown to increase interferon levels as well.[21]

In turn, a vitamin C deficiency results in a reduced resistance against certain germs.[22]

How Much Vitamin C Should You Take

Immune cell function is improved in people who supplement with at least 1g/day of vitamin C[23]. But it is also important to note that insufficient zinc levels impair phagocytosis and natural killer cell activity as well and, therefore, both nutrients play important roles in immune function to reduce the risk, severity, and duration of infectious diseases.[24]

I’ll cover the role of zinc in immunity another time but a large number of randomised controlled intervention trials, with daily intakes of up to 1g of vitamin C and up to 30mg of zinc, show that these nutrients – at this level – ameliorate symptoms and shorten the duration of respiratory tract infections including the common cold.[24]

Ideally, speak to your healthcare practitioner for a recommendation tailored personally to you. If you are currently dealing with a respiratory tract infection, ask them whether or not a Vitamin C Flush would also be helpful.

References:

1. Alberts B, Bray D, Lewis J, et al. Differentiated cells and the maintenance of tissues. In: Molecular Biology of the Cell. 3rd ed. New York: Garland Publishing, Inc.; 1994:1139-1193.
2. Jariwalla RJ, Harakeh S. Antiviral and immunomodulatory activities of ascorbic acid. In: Harris JR (ed). Subcellular Biochemistry. Vol. 25. Ascorbic Acid: Biochemistry and Biomedical Cell Biology. New York: Plenum Press; 1996:215-231.
3. Bergsten P, Amitai G, Kehrl J, et al. Millimolar concentrations of ascorbic acid in purified human mononuclear leukocytes. Depletion and reaccumulation. J Biol Chem. 1990;265(5):2584-2587.
4. Evans RM, Currie L, Campbell A. The distribution of ascorbic acid between various cellular components of blood, in normal individuals, and its relation to the plasma concentration. Br J Nutr. 1982;47(3):473-482.
5. Jariwalla RJ, Harakeh S. Mechanisms underlying the action of vitamin C in viral and immunodeficiency disease. In: Packer L, Fuchs J, eds. Vitamin C in Health and Disease. New York: Marcel Dekker, Inc.; 1997:309-322.
6. Wintergerst ES, Maggini S, Hornig DH. Immune-enhancing role of vitamin C and zinc and effect on clinical conditions. Ann Nutr Metab. 2006;50(2):85-94.
7. Young, J.W., Gluconeogenesis in Cattle: Significance and Methodology1. Journal of Dairy Science, 1977. 60(1): p. 1-15.
8. Sanchez A, Reeser JL, Lau HS, et al.  Role of sugars in human neutrophilic phagocytosis. Am J Clin Nutr 1973. Vol. 26 no. 11 1180-1184.
9. Krone CA, Ely JT. Controlling hyperglycemia as an adjunct to cancer therapy. Integr Cancer Ther. 2005 Mar;4(1):25-31.
10. Prinz W, Bortz R, Bregin B, et al. The effect of ascorbic acid supplementation on some parameters of the human immunological defence system. Int J Vitam Nutr Res. 1977;47(3):248-257.
11. Vallance S. Relationships between ascorbic acid and serum proteins of the immune system. Br Med J. 1977;2(6084):437-438.
12. Kennes B, Dumont I, Brohee D, et al. Effect of vitamin C supplements on cell-mediated immunity in old people. Gerontology 1983;29(5):305-310.
13. Panush RS, Delafuente JC, Katz P, et al. Modulation of certain immunologic responses by vitamin C. III. Potentiation of in vitro and in vivo lymphocyte responses. Int J Vitam Nutr Res Suppl. 1982;23:35-47.
14. Jariwalla RJ, Harakeh S. Antiviral and immunomodulatory activities of ascorbic acid. In: Harris JR (ed). Subcellular Biochemistry. Vol. 25. Ascorbic Acid: Biochemistry and Biomedical Cell Biology. New York: Plenum Press; 1996:215-231.
15. Levy R, Shriker O, Porath A, et al. Vitamin C for the treatment of recurrent furunculosis in patients with imparied neutrophil functions. J Infect Dis. 1996;173(6):1502-5.
16. Anderson R, Oosthuizen R, Maritz R, et al. The effects of increasing weekly doses of ascorbate on certain cellular and humoral immune functions in normal volunteers. Am J Clin Nutr. 1980;33(1):71-6.
17. Wintergerst ES, Maggini S, Hornig DH. Immune-enhancing role of vitamin C and zinc and effect on clinical conditions. Ann Nutr Metab. 2006;50(2):85-94. 
18. Anderson R, Oosthuizen R, Maritz R, et al. The effects of increasing weekly doses of ascorbate on certain cellular and humoral immune functions in normal volunteers. Am J Clin Nutr. 1980;33(1):71-6.
19. Levy R, Shriker O, Porath A, et al. Vitamin C for the treatment of recurrent furunculosis in patients with imparied neutrophil functions. J Infect Dis. 1996;173(6):1502-5.
20. Wintergerst ES, Maggini S, Hornig DH. Immune-enhancing role of vitamin C and zinc and effect on clinical conditions. Ann Nutr Metab. 2006;50(2):85-94.
21. Dahl H, Degré M. The effect of ascorbic acid on production of human interferon and the antiviral activity in vitro. Acta Pathol Microbiol Scand B. 1976;84B(5):280-4.
22. Ströhle A, Hahn A. Vitamin C and immune function. Med Monatsschr Pharm. 2009;32(2):49-54.
23. Casciari JJ, Riordan HD, Mikirova N, et al. Effect of Vitamin C Supplementation on Ex Vivo Immune Cell Functioning. Journal of Orthomolecular Medicine 2003 Vol. 18, No. 2, p83-92.
24. Wintergerst ES, Maggini S, Hornig DH. Immune-enhancing role of vitamin C and zinc and effect on clinical conditions. Ann Nutr Metab. 2006;50(2):85-94.