The 2014–2015 flu season is ­officially upon us. Meanwhile, nasty cold viruses have already been circulating for months, and the Ebola epidemic grows more out of control. I can’t remember a time I felt such a strong desire to strengthen my immune system. You already know the basics—wash your hands, get enough sleep, reduce stress, exercise, eat ahealthy diet, take immune boosting supplements, etc.—so I’m going to examine what I think are two of the most critical steps you can take to get your immune system functioning optimally.

Cut down on sugar in all its forms

Within 30 minutes of ingesting any form of sugar, including honey and fruit juice—and for at least five hours afterwards—your immune system is majorly stunted.1 Sugar significantly lowers the ability of white blood cells called neutrophils to destroy pathogens like the influenza virus.1 Normally, neutrophils engulf and devour microorganisms in a process called phagocytosis. But sugar inhibits phagocytosis by as much as 50% at the peak of inhibition, which usually occurs about two hours after sugar ingestion.1 The higher your blood sugar levels get, the more phagocytosis is inhibited, and the more your immune system is compromised.2 This is bad news if you’ve recently come into contact with the influenza virus, because your neutrophils use phagocytosis to eliminate the virus soon after it invades your lung tissue.3

Further, sugar increases low-grade inflammation throughout the body, which also appears to make you more likely to get the flu.4,5 Incidentally, both stress and obesity also cause low-grade inflammation, which is why stressed-out people and people with obesity have been found to be at higher risk of becoming infected with the flu.5,6

Drs. Murray and Pizzorno, in The Textbook of Natural Medicine, recommend limiting sugar consumption (including fruit sugars) to less than 50 grams a day for general immune support.7 For reference, see the table above for the sugar content of a standard serving size of a small sample of foods, or use the USDA’s National Nutrient Database for complete nutritional information of foods. Note, in case you’re a sucrolase (Splenda) fan, don’t assume that substituting this type of artificial sweetener will keep your immune system protected—it now appears that through entirely different mechanisms, sucralose may also prevent you from mounting an effective immune response when exposed to pathogens like the flu virus.8

Zinc

Of all the vitamins and minerals you can possibly take to improve your immune function and prevent colds, flu and respiratory tract infections, zinc is the most important. Zinc deficiency is commonly overlooked in developed countries like the United States,9 but even a mild deficiency, in which blood levels are within the normal range, impairs immune function, decreasing the activity of two important immune cells: natural killer and T helper cells.10 These lymphocytes (white blood cells) play a major role eradicating virally infected cells.
Whether you have a mild zinc deficiency or not, daily zinc supplementation can significantly decrease your chance of coming down with a respiratory infection.12-16 If you do still catch a cold while taking zinc, chances are you will have fewer symptoms and they won’t last as long.12

For the best absorption, take zinc amino acid chelate, such as zinc picolinate or glycinate, rather than zinc gluconate, sulfate, or oxide.11 You will likely get the best resuts from taking this form of zinc along with an additional multivitamin/mineral; nutrients work in sync, and the combination of zinc and other vitamins and minerals may be particularly good at increasing white blood cells and boosting immune function.17 Children should take between 15 and 20 mg per day, and adults should take between 30 and 50 mg per day. Make sure your multivitamin contains copper to prevent zinc-induced copper deficiency.

Staying well is a challenge when the cold and flu is raging all around you, but keeping your immune system healthy by avoiding sugar and taking zinc goes a long way. Just by following either of these two recommendations, you can greatly reduce your chance of getting sick this flu season. Of course, there are many additional foundational steps that are critical in strengthening your immune function. Nothing can replace these basics: water, sleep, regular exercise, stress reduction, and healthy foods, especially those rich in vitamin C (citrus fruits, kiwi, strawberries, red and green peppers, tomatoes, cantaloupe), and other immune building compounds (onions, garlic, mushrooms, ginger, herbs and spices, probiotics, and fatty fish). Help your immune system thrive by taking these simple, yet powerful, steps this cold and flu season.

1. Am J Clin Nutr. 1973 Nov;26(11):1180-4.
2. Textbook of Natural Medicine. 2013: p. 518.
3. J Immunol. 2007;178:2448-2457.
4. Nutr J. 2014;13:61.
5. Stud Pulse. 2013;5:(09).
6. J Bacteriol Virol. 2014 Sep;44(3):226-235.
7. Textbook of Natural Medicine. 2013: p. 521.
8. J Immunoassay Immunochem. 2014;35(1):26-36.
9. Curr Opin Pediatr. 2014 Oct;26(5):579-84.
10. Adv Nutr. 2013 Mar 1;4(2):176-90.
11. Int J Vitam Nutr Res. 2007 Jul;77(4):243-8.
12. Paediatr Int Child Health. 2013 Aug;33(3):145-50.
13. Cochrane Database Syst Rev. 2011 Feb 16;(2):CD001364.
14. Am J Public Health. 2010 June; 100(6): 970–971.
15. Clin Nutr. 2013 Apr;32(2):193-9.
16. Pediatrics. 2007 Jun;119(6):1120-30.
17. Am J Clin Nutr. 2008 Oct;88(4):1067-73.