Useful vitamin supplements during flu season

Help build your patients’ immunity during flu season by recommending the proper vitamin supplements together with the right health and wellness plan.

This is the time of year we begin to worry about viruses. However, we have more to worry about than the flu this year, including COVID and RSV. While the medical establishment sells vaccines as the only answer to immunity, there are helpful vitamin supplements. This may be obvious, but it is worth mentioning that you don’t really fight a virus with supplements. Your body is already fighting it, you are just supplying it with some ammunition. However, supplementing can help your immune system do its job. This article presents a review of some useful supplements to help prevent the flu and other viruses.

Vitamin supplements to build immunity

Vitamin A

Animal studies

Vitamin A levels plummet with infection and with chemical exposure. Some studies report the use of vitamin supplements to be valuable in protecting against viral infections. There are a number of animal studies showing vitamin A as antiviral. One study showed it alleviated inflammatory responses in reproductive tracts of male mice infected with pseudorabies virus.1 Another animal study showed vitamin A improves IgA production in the mucosa.2 Vitamin A deficient mice have increased viral antigens and enhanced cytokine/chemokine production in nasal tissues following respiratory virus infection, according to another study.3

Vitamin A is important for membrane health. One study looked at alveolar membranes in rats. Researchers concluded, “Vitamin A deficiency results in alterations of the structure and composition of the alveolar BM which are probably mediated by TGF-beta1 and reverted by retinoic acid.”8

In another animal study researchers stated, “In conclusion, vitamin A deficiency suppressed the immunity of the airway by decreasing the IgA and mucin concentrations in neonatal chicks. This study suggested a suitable level of vitamin A is essential for the secretion of IgA and mucin in the respiratory tract by regulating the gene expression of cytokines and epithelial growth factors.”9

Vitamin A and vitamin D are important for the health of the gut membrane. So much so, that deficiency can affect the microbiota, and thus the immune system. Researchers in one study state, “There are some unique functions of vitamin A and D; for example, vitamin A induces gut homing receptors on T cells, while vitamin D suppresses gut homing receptors on T cells. Together, vitamin A- and vitamin D-mediated regulation of the intestinal epithelium and mucosal immune system shape the microbial communities in the gut to maintain homeostasis.”10

Human studies

Human studies exist as well. One study showed supplementation to be helpful for both measles and RSV.4 There are several studies involving HIV infected children and vitamin A. One study demonstrated a reduction in mortality in HIV infected children.5 Another study showed vitamin supplements reduced mortality in patients infected with Ebola virus.6 Supplementation with vitamin A may potentiate vaccines. Researchers concluded in one study, “Overall, our study demonstrates vitamin A&D supplementation can improve immune responses to vaccines when children are vitamin A and D-insufficient at baseline. Results provide guidance for the appropriate use of vitamins A and D in future clinical vaccine studies.”7


When giving vitamin C, consider giving quercetin. The two supplements seem to potentiate each other.

Quercetin has unique biological properties that may improve mental/physical performance and reduce infection risk.11,12 It has strong anti-inflammatory capabilities demonstrated in in vitro, animal and human studies.11,12

Quercetin has been studied in various models of viral infection and shows promising antiviral effects. It inhibits polymerases,13 proteases,14 reverse transcriptase,15 suppressing DNA gyrase and binding viral capsid proteins.16,17

One article recommended the combination of vitamin C and quercetin as an effective and inexpensive way to help COVID patients.18 The authors stated, “Quercetin displays a broad range of antiviral properties which can interfere at multiple steps of pathogen virulence -virus entry, virus replication and protein assembly; these therapeutic effects can be augmented by the co-administration of vitamin C. Furthermore, due to their lack of severe side effects and low-costs, we strongly suggest the combined administration of these two compounds for both the prophylaxis and the early treatment of respiratory tract infections, especially including COVID-19 patients.”18


It is worth mentioning glandulars because there is a tradition in chiropractic offices to use glandulars. There is evidence glandular supplements target the same organ in the consumer as produced by the animal. Axel Kment, MD, demonstrated through radioactive isotope tracing of specific factors from glandular tissues are transported by the bloodstream and absorbed by the corresponding glands of the patient. This has been supported by other research.20 Another study found glandular extracts from liver, lung and thyroid specifically targeted those organs.19 Thymus extracts have been shown to support cellular immunity and to be beneficial to patients with immunodeficiency.20,21 Thymus extracts have also been shown to increase the activity of T cells and B cells.22-24

Vitamin supplements to treat inflammation

An infection is like chemical warfare. During an infection, lymphocytes secrete inflammatory proteins, such as cytokines, to destroy the invader. Free radicals are also generated. This is a big problem for people with long-term viral infections.

Inflammation is a component of every disease; 60% of Americans have a chronic disease. This means at least 60% of us are inflamed. COVID-19 killed a million people and hospitalized more, not because of the virus, but because of inflammation.

While it is useful to recommend a vitamin supplement for a patient that supports immune activity, it is vital you teach them about inflammation. You can control inflammation with vitamin supplements coupled with a healthy diet.


  1. Fang ZF, et. al. Vitamin a supplements alleviate inflammatory responses in reproductive tracts of male mice infected with pseudorabies virus. Int J Vitam Nutr Res. 2010;80(2):117-30. PubMed website. Accessed Nov. 6, 2023.
  2. Oral retinyl palmitate or retinoic acid corrects mucosal IgA responses toward an intranasal influenza virus vaccine in vitamin A deficient mice. 2014;32(22):2521-4. PubMed website. Accessed Nov. 6, 2023.
  3. Penkert RR, et. al. Vitamin A deficient mice exhibit increased viral antigens and enhanced cytokine/chemokine production in nasal tissues following respiratory virus infection despite the presence of FoxP3+ T cells. PubMed website. Accessed Nov. 6.
  4. Kawasaki Y, et. al. The efficacy of oral vitamin A supplementation for measles and respiratory syncytial virus (RSV) infection. Kansenshogaku Zasshi.1999;73(2):104-9. PubMed website. Accessed Nov. 6, 2023.
  5. Semba RD, et. al. Effect of periodic vitamin A supplementation on mortality and morbidity of human immunodeficiency virus-infected children in Uganda: A controlled clinical trial. 2005;21(1):25-31. PubMed website. Accessed Nov. 6, 2023.
  6. Aluisio AR, et. al. Vitamin A Supplementation Was Associated with Reduced Mortality in Patients with Ebola Virus Disease during the West African Outbreak. J Nutr. 2019;149(10):1757-1765. PubMed website. Accessed Nov. 6, 2023.
  7. Patel N, et. al. Baseline Serum Vitamin A and D Levels Determine Benefit of Oral Vitamin A&D Supplements to Humoral Immune Responses Following Pediatric Influenza Vaccination. 2019;11(10). PubMed website. Accessed Nov. 6, 2023.
  8. Esteban-Pretel G, et. al. Vitamin A deficiency alters rat lung alveolar basement membrane: reversibility by retinoic acid. J Nutr Biochem. 2010;21(3):227-36. PubMed website. Accessed Nov. 6, 2023.
  9. Fan X, et. al. Vitamin A Deficiency Impairs Mucin Expression and Suppresses the Mucosal Immune Function of the Respiratory Tract in Chicks. PLoS One. 2015;10(9):e0139131. PubMed website. Accessed Nov. 6, 2023.
  10. Cantorna MT, et. al. Vitamin A and vitamin D regulate the microbial complexity, barrier function, and the mucosal immune responses to ensure intestinal homeostasis. Crit Rev Biochem Mol Biol. 2019;54(2):184-192. PubMed website. Accessed Nov. 6, 2023.
  11. Nabavi SM, et. al. In vivo protective effects of quercetin against sodium fluoride-induced oxidative stress in the hepatic tissue. Food Chem. 2012;132:931–935. Science Direct. Nov. 6, 2023.
  12. Shinozuka K, et. al. Inhibitory effect of flavonoids on DNA-dependent DNA and RNA polymerases. Experientia. 1988;44:882–5. PubMed website. Accessed Nov. 6, 2023.
  13. Bachmetov L, et. al. Suppression of hepatitis C virus by the flavonoid quercetin is mediated by inhibition of NS3 protease activity. J Viral Hepat. 2012;19:81–88. PubMed website. Accessed Nov. 6, 2023.
  14. Spedding G, et. al. Inhibition of reverse transcriptases by flavonoids. Antiviral Res. 1989;12:99–110. PubMed website. Accessed Nov. 6, 2023.
  15. Cushnie TPT, Lamb AJ, et. al. Antimicrobial activity of flavonoids. Int J Antimicrob Agents. 2005;26:343–356. PubMed website. Accessed Nov. 6, 2023.
  16. Debiaggi M, et. al.Effects of propolis flavonoids on virus infectivity and replication. Microbiologica. 1990;13:207–13. PubMed website. Accessed Nov. 6, 2023.
  17. Awad HM, et. al. Peroxidase-catalyzed formation of quercetin quinone methide-glutathione adducts. Arch Biochem Biophys. 2000;378:224–233. PubMed website. Accessed Nov. 6, 2023.
  18. Terao J. Dietary flavonoids as antioxidants in vivo: conjugated metabolites of (-)-epicatechin and quercetin participate in antioxidative defense in blood plasma. J Med Invest. 1999;46:159–168. PubMed website. Accessed Nov. 6, 2023.
  19. Santoro RL, Weyhreter AF. Support of human gland/organ function with raw protein concentrate as measured by improvement in serum chemistry values. J Applied Nutrition. 1993;45(2):48-60. EurekaMag website. Accessed Nov. 6, 2023.
  20. Stein J. Objective demonstration of the organ specific effectiveness of cellular preparations. Schmid F, ed. Cell Research and Cellular Therapy. Ott Publsihers:Thoune (Switzerland). 1967:295-301.
  21. Lin CY, et al. Treatment of combined immunodeficiency with thymic extract. Annals Allergy. 1987;58: 379-384. PubMed website. Accessed Nov. 6, 2023.
  22. Kouttab NM, et. al. Thymomodulin: biological properties and clinical applications. Med Oncol Tumor Pharmacother. 1989;6(1):5-9. PubMed website. Accessed Nov. 6, 2023.
  23. Kouttab NJ, et. al. Production of human B and T cell growth factors is enhanced by thymic hormones. Immunopharmacology. 1988;16(2):97-105. PubMed website. Accessed Nov. 6, 2023.
  24. Cazzola P, et. al. Update and future perspectives of a thymic biological response modifier. Immunopharmacol Immunotoxicol.1987;9(2-3):195-216. PubMed website. Accessed Nov. 6, 2023.