Here are 7 important nutrients to boost your immunity, reduce inflammation and support the respiratory tract so that you’re in the best state of health to fight the flu this winter. Dietary sources of these nutrients that are relevant for the flu are included. However, nutritional supplements may also be required in order to provide therapeutic doses and treat specific deficiencies.

1. Vitamin A

In addition to its role in eye health, helps to maintain the integrity of the tissue lining the respiratory tract. This forms an important barrier against micro-organisms.

Vitamin A is also needed for proper functioning of immune cells and a deficiency in serum vitamin A has been associated with recurrent respiratory tract infections in children¹.

Foods To Eat: Recommended food sources of vitamin A include cod liver oil, poultry, cornmeal, egg yolks. Beta-carotene, the precursor of vitamin A, is found in pumpkin, carrots, sweet potato, green leafy vegetables, broccoli, red capsicum, mango and apricots².

2. Vitamin C

It is well known as an essential antioxidant and cold and flu remedy. It stimulates the production and function of specific immune cells and increases the expression of the gene for glutathione peroxidase, a major antioxidant². It has been reported that vitamin C might play an important role in stress and the response to stress hormones. It also reduced inflammation and prevented the development of pneumoniae in restraint-stressed mice⁴. High doses used at the onset of symptoms is necessary for reducing the duration of symptoms.

Foods To Eat: Some important food sources of vitamin C are red chilli, guava, red capsicum, brussels sprouts, citrus juice concentrate, papayas, kale, parsley, collards, kiwi fruit, blackcurrants, mango, cabbage, broccoli, strawberries, lychees, oranges, sprouts, lemons, tangerines, honeydew melon, spinach and tomatoes².

3. Vitamin E

It has an important role in the development of children, reproductive health, and vision. It is a major lipid-soluble antioxidant of all cell membranes that helps to reduce the risk of chronic diseases. Furthermore, laboratory and animal studies suggest a role of vitamin E in enhancing cellular and humoral immunity^4,5. This is supported by clinical studies that have found an increased risk of acute and recurrent respiratory tract infections associated with inadequate serum levels of vitamin E in children ^1,6 and elderly patients⁷.

Foods To Eat: Foods rich in vitamin E include wheatgerm and wheatgerm oil, soybean oil, almonds, sunflower seeds, walnuts, cashews, avocado and brown rice².

4. Zinc

Zinc supports the immune system by reducing skin barrier function and decreasing the ability of immune cells to respond to micro-organisms. Zinc also modulates inflammatory cytokines and was shown to improve the severity of symptoms of the common cold in children⁸. Zinc deficiency decreases cell-mediated immunity and zinc supplementation in elderly subjects decreased the incidence of infection by nearly 66%⁹.

Foods To Eat: Zinc is found in red meat, fish, sesame seeds, sunflower seeds, pepitas, walnuts, almonds, muesli, lentils, wheatgerm, ginger root, pecans, wholegrains, sardines and split peas².

5. Coenzyme Q10

Coenzyme Q10 is a potent, fat-soluble antioxidant vitamin necessary for energy production in cells. It requires eight vitamin coenzymes to function: tetrahydrobiopterin, vitamins B6, C, B2, B3, B5, B12 and folic acid¹⁰. So if any of these are deficient in the body, CoQ10 won’t work properly. It also helps to regenerate vitamin E. In a small clinical study of children with the H1N1 influenza virus, serum levels of CoQ10 and zinc were significantly reduced, which correlated with increased severity of damage in lung tissue¹¹.

Foods To Eat: Meat and fish products contain the most concentrated amounts of CoQ10, although some is found in boiled broccoli, cauliflower, nuts, spinach and soy¹⁰.

6. Vitamin D

Vitamin D is emerging as a major vitamin that is not only important for healthy bones and disease prevention. Vitamin D has many mechanisms of action, including a role in enhancing one’s immunity. More specifically, it inhibits the production of inflammatory substances from immune cells ¹².

Furthermore, high-dose vitamin D supplementation may be suitable for the prevention of seasonal influenza, as shown by shorter durations of fever, cough, and wheezing in children with influenza A infection compared with low dose vitamin D supplementation¹³. Another investigation found that taking vitamin D3 orally reduces the risk for acute respiratory tract infection in children and adults¹⁴.

Foods To Eat: Small amounts of the nutrient, vitamin D are found in meats (of animals exposed to sunlight), fatty fish, such as herring, salmon and sardines, beef and liver, cod liver oil, butter and eggs¹⁰.

7. Probiotics

Probiotics are live, beneficial microorganisms which promote immune balance not only in the gut, but they can also influence how other organs function. Since more than 70% of our immune system resides in the gut, it makes sense to ensure an optimal environment in the intestinal microbiome.

Specific strains and blends of probiotics have been found to be effective in activating the body’s own immune response against viral and bacterial pathogens. For example, a group of volunteers who took specific strains of Lactobacillus plantarum, Lactobacillus rhamnosus, Bifidobaterium lactis plus fructooligosaccharides had fewer and less severe flu episodes the following winter compared with the placebo group¹⁵.

In another clinical study, B.subtilis CU1, was found to reduce the frequency of respiratory infections in healthy elderly subjects compared to the placebo group. This is thought to be due to enhanced production of the body’s natural secretory antibodies that line the respiratory tract¹⁶.

In addition, probiotics may modify the release of inflammatory substances in the lungs and clear out the virus faster after influenza infection¹⁷.

Foods To Eat: Traditional fermented foods, such as sauerkraut, kim chi, tempeh, kefir and the increasingly popular drink kombucha are rich sources of probiotic organisms. Yoghurt contains small amounts of probiotics, but the therapeutic value is quite low in most commercially available yoghurts¹⁰.

More Information

For further information on dietary & lifestyle tips and taking herbs & nutrients for fighting the flu, see Dr Reimann’s other blogs here.

References

1. Zhang et al. (2016). Low Serum Levels of Vitamins A, D, and E are associated with Recurrent Respiratory Tract Infections in Children Living in Northern China: A Case Control Study. PLOS ONE 11(12): e0167689. doi:10.1371/journal.pone.0167689
2. Hechtman, L. (2015). Clinical Naturopathic Medicine - E-Book. Churchill Livingstone. VitalBook file.
3. Min YN et al. (2018). Vitamin E and vitamin C supplementation improves antioxidant status and immune function in oxidative-stressed breeder roosters by up-regulating expression of GSH-Px gene. Poultry Science. 97 (4): 1238-1244
4. Cai Y et al. (2015). A New Mechanism of Vitamin C Effects on A/FM/1/47(H1N1) Virus-Induced Pneumonia in Restraint-Stressed Mice. BioMed Research International. Article ID 675149, 12 pages https://dx.doi.org/10.1155/2015/675149
5. Muir WI et al. (2002). Dietary supplementation with vitamin E modulates avian intestinal immunity. The British Journal of Nutrition. 87 (6): 579-85
6. Qi et al. (2016). Relationship between deficiencies in vitamin A and E and occurrence of infectious diseases among children. European Review for Medical and Pharmacological Sciences. 20: 5009-5012
7. Wu D & Meydani SN, (2014). Age-associated changes in immune function: impact of vitamin E intervention and the underlying mechanisms. Endocrine, Metabolic & Immune Disorders Drug Targets. 14 (4): 283-9
8. Kurugol et al (2007). Effect of zinc sulfate on common cold in children: randomized, double blind study. Pediatrics International: Official Journal Of The Japan Pediatric Society. 49 (6): 842-7
9. Prasad, AS (2013). Discovery of human zinc deficiency: its impact on human health and disease. Advances In Nutrition. 4 (2): 176-90
10. Braun, L & Cohen, M. (2015). Herbs & Natural Supplements. An evidence-based guide. Vol. 2 (4^th). Elsevier Australia
11. Kelekci, S et al. (2012). The relationships between clinical outcome and the levels of total antioxidant capacity (TAC) and coenzyme Q (CoQ10) in children with pandemic influenza (H1N1) and seasonal flu. European Review for Medical and Pharmacological Sciences. 16: 1033-1038
12. Thien, R et al. (2013). Interactions of 1 alpha,25-dihydroxyvitamin D3 with IL-12 and IL-4 on cytokine expression of human T lymphocytes. The Journal Of Allergy And Clinical Immunology. 116 (3): 683-9
13. Zhou, J et al. (2008). Preventive Effects of Vitamin D on Seasonal Influenza A in Infants: A Multicenter, Randomized, Open, Controlled Clinical Trial. The Pediatric Infectious Disease Journal. ISSN: 1532-0987
14. Sacks, H.S (2017). 2017 - Review: In children and adults, vitamin D3 supplementation reduces risk for acute respiratory tract infection. American College of Physicians Journal Club, 5/16/2017; 166(10): 2-2.
15. Pregliasco, F et al (2008). A New Chance of Preventing Winter Diseases by the Administration of Synbiotic Formulations. J Clin Gastroenterol. 42:S224–S233
16. Lefevre M et al. (2015). Probiotic strain Bacillus subtilis CU1 stimulates immune system of elderly during common infectious disease period: a randomized, double-blind placebo-controlled study. Immunity & Ageing. 12, pp. 24-35
17. Belkacem N et al. (2017). Lactobacillus paracasei feeding improves immune control of influenza infection in mice. PLoS ONE 12
18. (9): e0184976. https://doi.org/10.1371/journal.pone.0184976

Article by Dr Amanda Reimann, Medical Herbalist & Biochemist at ATUNE Health Centres.