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Cold & Flu Season

During Cold & Flu Season, Protect Yourself by Eating Right

Cold and flu are a larger burden than we may think. Between treatments, illness-compromised productivity, and lost workdays, it is estimated that the common cold alone costs the U.S. $40 billion each year.1

We all know the basics for reducing exposure—wash your hands, avoid touching your face, and avoid being exposed to people who are already ill. Some people may choose the influenza vaccine, however it is important to know that it is not very effective. An independent analysis of flu vaccine studies by the Cochrane Collaboration found that under typical conditions, 100 people need to be vaccinated to avoid one set of influenza symptoms or you would have to be vaccinated every year for 100 years, to save yourself one flu episode. Interestingly, the study showed that flu vaccine did NOT significantly affect the number of people hospitalized or working days lost, and did not prevent flu–associated complications or those rare flu–associated deaths.2,3

Those of us who eat healthfully need not worry about the dangers of the flu. Excellent nutrition can reduce our vulnerability to infection and reduce the length and severity of illness if we do become infected. Many micronutrients are required to support proper function of the immune system, and phytochemicals from colorful produce have additional anti-microbial and immune-boosting effects.


Mushrooms have a unique ability to activate the body’s natural immune defenses. Reishi and shiitake mushrooms enhance activity of natural killer (NK) cells, which attack cancerous and virus-infected cells.4,5 Shiitake mushrooms protect against influenza infection in animal studies.6-8 Fortunately though, it is not only exotic mushrooms that benefit the immune system. Eating white button mushrooms daily was found to enhance immune defenses in mucosal linings such as those in the mouth and respiratory tract.9 Dendritic cells are another type of immune cell that protects the respiratory tract, and their activity is also enhanced by white button mushroom phytochemicals.10Mushrooms should only be eaten cooked: several raw culinary mushrooms contain a potentially harmful compound called agaritine, and cooking mushrooms significantly reduces the agaritine content.11,12

Cruciferous vegetables

The cruciferous family of vegetables includes kale, collards, mustard greens, arugula, watercress, broccoli, broccoli rabe, cabbage, cauliflower, kohlrabi, and more. The bitter, spicy or pungent flavors of these vegetables are provided by glucosinolates, which are converted into potent anti-cancer compounds, called isothiocyanates (ITCs), upon chopping or chewing. In addition to their anti-cancer effects, ITCs also support the immune system and have antimicrobial properties. Cruciferous vegetable phytochemicals may enhance interferon activity, which is an important component of the body’s antiviral response.13,14 To maximize ITCs, chop cruciferous vegetables finely, eat them raw and chew them well; the enzyme that converts glucosinolates to ITCs (called myrosinase) is activated by disrupting the plant cells and deactivated by heat. However, you can still get ITCs from your cooked cruciferous vegetables: chop them finely before you begin to cook and add some raw cruciferous to the meal. For instance, if you are eating cooked broccoli, add some shredded cabbage to your salad, which will provide some myrosinase to produce more ITC from the already cooked broccoli. Gut bacteria have the myrosinase enzyme, so a small amount of ITCs from cooked cruciferous vegetables will be produced in the digestive tract as well.


Berries are powerful anti-cancer foods that also offer protection against viruses. Antioxidants called flavonoids, which are abundant in berries, have antiviral activity.15 In fact, if you do get the flu, taking anthocyanin-rich elderberry juice may even shorten the duration of your symptoms.16-18Berries and grapes are also rich in resveratrol, another antioxidant phytochemical with strong antiviral effects—resveratrol has been shown to block the replication of influenza and other respiratory viruses.19-21 Plus, strawberries are high in vitamin C, which protects immune cells from oxidative damage.22 The benefits of berries go far beyond cold and flu protection. Flavonoid antioxidants like those in berries are not just antioxidants—flavonoids also act on signaling within the cell leading to many beneficial effects: flavonoids activate the body’s natural detoxification enzymes, block the growth of cancer cells, decrease inflammation, and support proper blood pressure regulation.23Berries (and pomegranates) are also extremely rich in another antioxidant called ellagic acid, a compound known to block cancer cell and tumor growth.24-26

Onions & garlic

There is no convincing evidence for using garlic supplements for symptoms of the common cold.27However, eating garlic and onions daily has clear benefits when it comes to cancer prevention, and may also help to build immune defenses, including macrophage, T cell, and NK cell activity.28,29 Plus, several garlic phytochemicals have virus-killing activity against common respiratory viruses.30 Like cruciferous vegetables, the active compounds in onions and garlic are produced when the plant cells are disrupted, so they are best eaten raw, chopped finely and chewed well.

Appropriate supplements

Vitamin D and zinc are important players in immune function, so maintaining adequate stores of these micronutrients will also help to protect against cold and flu. Children given vitamin D supplements throughout the winter reduced the occurrence of flu compared to a placebo group, and taking supplemental zinc regularly was found to slightly reduce the number of colds caught by children.17,31Since vitamin D is not readily available in the food supply, and zinc is not highly absorbed from plant foods, well-designed supplements are a good choice.

If you do become ill:

If you do get a cold, treat it wisely. Many cold remedies are ineffective, and some may even prolong the illness. For example, megadoses of vitamin C do not prevent colds or reduce symptoms, and fever-reducing medications actually hinder the body’s attack on the infection. (In my book Super Immunity, I evaluate a number of common cold and flu remedies.)

Don’t be alarmed if your cold symptoms last longer than you expect. On average, patients report that their common cold symptoms last one and a half to two weeks. In children, earaches tend to last anywhere from less than one day to 9 days, sore throat 2 to 7 days, cough up to 25 days, and the common cold 7 to 15 days.32 In time, the body will clear the virus on its own. Remember, over-the-counter medications merely mask symptoms, and may even impair healing. However, if you experience a sudden worsening of symptoms, especially including labored breathing, or a fever above 103 degrees for three days, then it is time to call the doctor.


1. Fendrick AM, Monto AS, Nightengale B, et al: The economic burden of non-influenza-related viral respiratory tract infection in the United States. Arch Intern Med 2003;163:487-494. 
2. Jefferson T, Di Pietrantonj C, Rivetti A, et al: Vaccines for preventing influenza in healthy adults. Cochrane Database Syst Rev2010:CD001269. 
3. Cochrane Summaries: Vaccines to prevent influenza in heatlthy adults. [http://summaries.cochrane.org/CD001269/vaccines-to-prevent-influenza-in-healthy-adults
4. Wachtel-Galor S, Yuen J, Buswell JA, et al: Ganoderma lucidum (Lingzhi or Reishi): A Medicinal Mushroom. In Herbal Medicine: Biomolecular and Clinical Aspects. 2nd edition. Edited by Benzie IFF, Wachtel-Galor S. Boca Raton (FL); 2011 
5. Yamaguchi Y, Miyahara E, Hihara J: Efficacy and safety of orally administered Lentinula edodes mycelia extract for patients undergoing cancer chemotherapy: a pilot study. Am J Chin Med 2011;39:451-459. 
6. Ciric L, Tymon A, Zaura E, et al: In vitro assessment of shiitake mushroom (Lentinula edodes) extract for its antigingivitis activity. J Biomed Biotechnol 2011;2011:507908. 
7. Rincao VP, Yamamoto KA, Ricardo NM, et al: Polysaccharide and extracts from Lentinula edodes: structural features and antiviral activity. Virol J 2012;9:37. 
8. Suzuki F, Suzuki C, Shimomura E, et al: Antiviral and interferon-inducing activities of a new peptidomannan, KS-2, extracted from culture mycelia of Lentinus edodes. J Antibiot (Tokyo) 1979;32:1336-1345. 
9. Jeong SC, Koyyalamudi SR, Pang G: Dietary intake of Agaricus bisporus white button mushroom accelerates salivary immunoglobulin A secretion in healthy volunteers. Nutrition 2012;28:527-531. 
10. Ren Z, Guo Z, Meydani SN, et al: White button mushroom enhances maturation of bone marrow-derived dendritic cells and their antigen presenting function in mice. J Nutr 2008;138:544-550. 
11. Toth B, Erickson J: Cancer induction in mice by feeding of the uncooked cultivated mushroom of commerce Agaricus bisporus. Cancer Res 1986;46:4007-4011. 
12. Schulzova V, Hajslova J, Peroutka R, et al: Influence of storage and household processing on the agaritine content of the cultivated Agaricus mushroom. Food Addit Contam 2002;19:853-862. 
13. Higdon J, Delage B, Williams D, et al: Cruciferous vegetables and human cancer risk: epidemiologic evidence and mechanistic basis. Pharmacol Res 2007;55:224-236. 
14. Xue L, Pestka JJ, Li M, et al: 3,3'-Diindolylmethane stimulates murine immune function in vitro and in vivo. The Journal of nutritional biochemistry 2008;19:336-344. 
15. Naithani R, Huma LC, Holland LE, et al: Antiviral activity of phytochemicals: a comprehensive review. Mini Rev Med Chem2008;8:1106-1133. 
16. Kelly GS: Quercetin. Monograph. Altern Med Rev 2011;16:172-194. 
17. Roxas M, Jurenka J: Colds and influenza: a review of diagnosis and conventional, botanical, and nutritional considerations. Altern Med Rev 2007;12:25-48. 
18. Zakay-Rones Z, Thom E, Wollan T, et al: Randomized study of the efficacy and safety of oral elderberry extract in the treatment of influenza A and B virus infections. J Int Med Res 2004;32:132-140. 
19. Campagna M, Rivas C: Antiviral activity of resveratrol. Biochem Soc Trans 2010;38:50-53. 
20. Xie XH, Zang N, Li SM, et al: Resveratrol Inhibits Respiratory Syncytial Virus-Induced IL-6 Production, Decreases Viral Replication, and Downregulates TRIF Expression in Airway Epithelial Cells. Inflammation 2012;35:1392-1401. 
21. Palamara AT, Nencioni L, Aquilano K, et al: Inhibition of influenza A virus replication by resveratrol. J Infect Dis2005;191:1719-1729. 
22. Oregon State University. Linus Pauling Institute: Micronutrient Information Center. Vitamin C.[http://lpi.oregonstate.edu/infocenter/vitamins/vitaminC/index.html
23. Higdon J: Flavonoids. In An Evidence-Based Approach to Dietary Phytochemicals. New York: Thieme; 2006: 114-126 
24. Adams LS, Zhang Y, Seeram NP, et al: Pomegranate ellagitannin-derived compounds exhibit antiproliferative and antiaromatase activity in breast cancer cells in vitro. Cancer Prev Res (Phila) 2010;3:108-113. 
25. Wang N, Wang ZY, Mo SL, et al: Ellagic acid, a phenolic compound, exerts anti-angiogenesis effects via VEGFR-2 signaling pathway in breast cancer. Breast Cancer Res Treat 2012;134:943-955. 
26. Anitha P, Priyadarsini RV, Kavitha K, et al: Ellagic acid coordinately attenuates Wnt/beta-catenin and NF-kappaB signaling pathways to induce intrinsic apoptosis in an animal model of oral oncogenesis. Eur J Nutr 2011. 
27. Lissiman E, Bhasale AL, Cohen M: Garlic for the common cold. Cochrane Database Syst Rev 2012;3:CD006206. 
28. Lau BH, Yamasaki T, Gridley DS: Garlic compounds modulate macrophage and T-lymphocyte functions. Mol Biother1991;3:103-107. 
29. Hassan ZM, Yaraee R, Zare N, et al: Immunomodulatory affect of R10 fraction of garlic extract on natural killer activity.Int Immunopharmacol 2003;3:1483-1489. 
30. Weber ND, Andersen DO, North JA, et al: In vitro virucidal effects of Allium sativum (garlic) extract and compounds. Planta Med 1992;58:417-423. 
31. Urashima M, Segawa T, Okazaki M, et al: Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr 2010;91:1255-1260. 
32.Thompson M, Vodicka TA, Blair PS, et al: Duration of symptoms of respiratory tract infections in children: systematic review. Br Med J 2013;347.

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