Doctor's Review: Medicine on the Move

January 20, 2022
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Food to fight the flu?


Many studies have shown the benefits of probiotics. Besides competing with harmful bacteria and viruses for places on epithelial cells, they can reduce and ameliorate diarrhea. They also activate macrophages and increase the numbers of cytokines, natural-killer cells and immunoglobulins, thereby protecting your body from the flu.1

To receive beneficial protective effects in relation to diarrhea, you must consume 1 to 10 billion (109-1010 cfu) bacteria daily.2 No dose for an immune response is currently available. One 100-g container of Activia yogurt contains 1 billion bacteria.3


Vitamin C: Years of study still haven’t proved that vitamin C protects you from a virus, however mega doses may cause digestive problems. Consume one to two oranges, kiwis or a serving of broccoli to receive your required daily amount. 4

Zinc: Vegetarians or seniors who consume less animal protein may be at risk of low zinc. Receive your recommended daily allowance of 8 mg if you are female and 11 mg if you are male by consuming seafood, animal protein, legumes, nuts and seeds, in portion sizes recommended by Canada’s Food Guide.5

Selenium: Most Canadians aren’t deficient. Maintain your daily intake of 55 mcg by consuming nuts, seafood, pork and whole grains.6

Vitamin E: Vitamin E has been used to treat influenza, but large doses over 400 IU (268 mg) per day have been linked to increased mortality, shown in a meta-analysis review released in 2005.7 Following the dietary reference intake of 15 mg for both men and women over 19 is the safest bet.8

Natural supplements

Echinacea: Several years ago everyone was taking echinacea to prevent colds and flu, though it was proven ineffective in multiple studies. Echinacea can have an effect on ragweed allergies.

Garlic: While it has some antiviral properties, more research is needed to determine if garlic prevents colds and flu. Individuals taking warfarin should avoid garlic supplements as they increase the risk of bleeding.

Elderberry: Some studies have shown that this fruit extract may decrease the length and severity of the seasonal and H1N1 flus, though antiviral medications are still considered safer and more effective.

American ginseng: Ginseng may reduce the chances of a respiratory-tract infection, but more information is needed to prove this. If you’re on diabetes medications, this extract can decrease blood glucose, possibly causing a hypoglycemic reaction.9

Andrographis, astragalus, bee propolis, boneset, goldenseal, oscillococcinum, pau d’arco, and wild indigo have also been linked to cold and flu prevention. Ask your patients if they take natural supplements as there can be contraindications to certain medications and medical conditions.10 For more on natural supplements and products, go to the Natural Medicines Comprehensive database,


A 2009 review of the literature investigating exercise and respiratory tract infections concluded that regular moderate exercise reduces inflammation in the respiratory tract and activates immunity, thereby reducing the chance of contracting a respiratory-tract infection, one type being the flu. The review also concluded that extended intense exercise may have the opposite effect.11

Try light activity for 60 minutes or 30 minutes of moderate to vigorous activity daily. Go to Canada’s Physical Activity Guide for ideas of specific activities: .


  • 1 Kang SA, Kim HY, Malik KA, Parvez S. Probiotics and their fermented food products are beneficial for health. J of Appl. Microbio 2006; 100: 1171-85.
  • 2 PEN Website 2008. Probiotics background [cited 2009 Dec 8]. Accessed from:
  • 3 Activa Website 2004. The Activia effect [cited 2009 Dec 8]. Accessed from:
  • 4, 5, 6 Dietitians of Canada Website 2009. Eating well boosts your immunity [cited 2009 Dec 8]. Accessed from:
  • 7 Appel LJ, Dalal D, Guallar E, Miller ER, Pastor-Barriuso R, Riemersma RA. Meta-analysis: high-dosage vitamin E supplementation may increase all-cause mortality. Annals of Internal Medicine 2005; 142 (1): 37-46.
  • 8 USDA Website 2009. Dietary guidance: DRI tables [cited 2009 Dec 8]. Accessed from:
  • 9, 10 Natural Medicines Comprehensive Database 2009. Natural medicines in the clinical management of colds and flu [cited 2009 Dec 8]. Accessed from:
  • 11 Martin SA, Pence BD, Woods JA. Exercise and respiratory tract viral infections. Exerc & Sport Sc Reviews 2009; 37(4): 157-64.

This article was accurate when it was published. Please confirm rates and details directly with the companies in question.


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