The immune system is composed of a group of chemicals, cells, proteins and tissues that work together to destroy anything it perceives as a threat to our well-being.
Immune cells play a crucial role in the protection of our body against the many foreign substances, pathogens and viruses it comes into contact with every day. It is constantly working to keep us alive.
This article outline 10 anti-viral herbs and supplements that are known for their immune-enhancing properties.
Strengthening your immune system is vital to protecting your body from infection. Despite the complexity of the human body, what it requires to work optimally is quite basic. Eating nutritious foods, getting enough sleep, staying hydrated, avoiding processed foods and managing stress are some of the ways to boost your immunity.
However, due to industrialization and subsequent lack of nutrients in the soil as well as poor diet choices, many individuals are left with vitamin deficiencies. Research has found supplementing with certain minerals, vitamins and herbs may be beneficial in supporting our immune system and promoting longevity.
See below the Top 10 Immune-Boosting Herbs and Supplements:
#1. Vitamin C
Vitamin C (or its chemical form L-ascorbic acid) is known for its potent antioxidant and antiviral effects. It can be found in many foods including sweet potato, peppers, kale, broccoli, and citrus fruits, berries and more.
Several studies have found that consuming Vitamin C may activate an immune response against certain flu viruses. Research has shown that supplementing with L-ascorbic acid can enhance the immune response to pathogens by up-regulating the activity of natural killer (NK) cells and of T lymphocytes – immune cells that kill non-specific pathogens (NK) and specific antigens (T-cells) as well as produce immunological memory. Increasing the activity of these immune cells ensures the body is equipped to fight off a wide range of pathogenic microbes. 
Moreover, Vitamin C is a powerful antioxidant. Microbial infections cause oxidative stress in the body due to an increase in free radicals. By boosting Vitamin C uptake through food or Ascorbic acid supplements, Vitamin C is found to decrease oxidative damage, promoting health and lowering the risk of certain conditions. 
#2 Green Tea Extract
Another great anti-viral plant is Green Tea (Camelia sinensis). Green tea has been used in traditional medicines for thousands of years for its multiple health benefits, particularly as a strong antioxidant and antimicrobial agent. The main compound responsible for the herb’s therapeutic properties is a catechin called Epigallocatechin-3-O-gallate (EGCG).
Recent studies have suggested EGCG may possess antiviral capacities against a broad range of RNA and DNA viruses. This is linked to the compound’s ability to block the primary stages of a viral infection, i.e. the binding and entry of viruses into cells via the interference of viral membrane proteins. Green Tea can be enjoyed as a tea or taken as a dietary supplement for an extra health boost. 
Zinc is an important mineral and nutrient that is required for many processes in the body. Among many other functions, Zinc supports the immune system, is required for bone growth, helps with wound healing, eyesight, as well as brain development. Check out how the immune system functions in kids and infants!
Many published articles have suggested that zinc may reduce the severity and duration of common colds due to zinc’s ionophoric activity that has antiviral effects against rhinoviruses (i.e. common cold). The common cold occurs through a rhinovirus infection of nasal epithelial cells. The rhinovirus is a single-stranded RNA virus that is responsible for most upper respiratory tract infections. 
The virus binds to a type of receptor molecule found in the nasal epithelium called intracellular adhesion molecule-1 (ICAM-1).
Ionic zinc also has an affinity to the ICAM-1 receptor due to its electrical charge. By attaching to these receptors, Zinc blocks the virus from infecting the epithelial cells. Several other studies have concurred with these results. One study indicated a significant reduction in the severity of the symptoms associated with a cold, as long as zinc is taken within 24 hours of the onset of the symptoms. 
Quercetin & Rutin (Quercetin-3-O-rutinoside) are a naturally occurring polyphenol and flavonoid, best known for its potent anti-inflammatory and immune-enhancing abilities. Many foods like red onion, berries, elderberry, and green tea contain this important antioxidant.
Quercetin has long been revered for its antioxidant potential. Its phenolic properties allow it to neutralize the damage caused by free radicals via the donation of a hydrogen atom.
Recently, scientists have found supplementing with Quercetin may have anti-viral effects. In fact, several in-vitro experiments found Quercetin could inhibit the entry of certain viruses by blocking the receptors on cells to which the viruses enter, and possibly preventing certain infections. 
Moreover, certain Quercetin-rich foods like red onion also act as a mucolytic agent, which help to expel stuck mucous and relieve congestion in the lungs.
Elderberries are powerful bioflavonoids – naturally occurring compounds that are notorious for their anti-viral and antioxidant properties. Studies explored the effects of elderberries on immunity and indicated that these berries improve immune function through their ability to increase cytokine activity – signalling molecules that regulate immune responses and inflammation.
Furthermore, scientists have shown these fruits may offer important respiratory protective properties by helping to expel stuck mucous/phlegm from the lungs.
The fruit of the elderberry plant is usually sold as a syrup or in dried fruits (that can be made into a syrup at home by adding dried elderberries, raw honey and boiling water). The flower itself can also be consumed as a healthful tea. 
#6 N-Acetyl Cysteine (NAC)
N-acetyl cysteine (NAC) is the supplement form of cysteine, a semi-essential amino acid that plays an important role in respiratory and immune function. One of the most popular attributes of NAC is it helps the body produce glutathione, the body’s most important antioxidant, which helps the body fight free radical damage and promote longevity. 
In addition, NAC has been found to improve respiratory health by helping to break down phlegm and decreasing inflammation in the lungs. 
#7 Vitamin D
We all know Vitamin D is vital to our well-being. This fat-soluble vitamin plays a fundamental role in the proper functioning of our body and particularly our immune system.
The data regarding the importance of Vitamin D for our health is extensive. Research shows individuals with adequate Vitamin D levels have enhanced immune responses, decreased inflammation and are less prone to infections. 
Vitamin D is best absorbed through sun exposure. Twenty minutes a day of sunlight is ideal. However, due to geographical location, many get their vitamin D through daily supplement intake, to prevent a deficiency in this essential vitamin.
Baicalin is a phytonutrient with a long history of use in traditional Chinese medicine for its potent anti-inflammatory compounds and positive effects on the immune and circulatory function.
Baicalin is found to strengthen the immune system with its ability to neutralize pathogens. In vivo studies performed on mice showed oral administration of Baicalin was effective in inhibiting the proliferation of certain viruses, demonstrating the antiviral activity of Baicalin. 
Adaptogens help your body cope with stress – be it physical, environmental or emotional. They adapt to the bodies needs at a given time – i.e. if you are fatigued, they give you energy and help you focus (Cordyceps) and if you are too wired with anxiety, they calm you down (Rhodiola rosea, Reishi).
Their mechanism of action is through supporting and modulating the endocrine and immune system. In fact, Adaptogenic herbs are great for boosting immunity. Herbs like Astragalus, Withania somnifera and Panax ginseng all contain potent immune-protective properties as they help to reduce inflammation. 
#10 Other Herbs
There is a list of herbs that have been cited in herbal medical literature for their immune-boosting abilities. Some of these include:
- Ginger – mucolytic, enhances digestion, kills pathogens, strengthens immunity.
- Curcumin – powerful anti-inflammatory and improves immune function.
- Thyme – antimicrobial herb, great for the throat and upset stomach.
- Echinacea – contain anti-viral properties, especially improve respiratory health. 
1 Kim, Y., Kim, H., Bae, S., Choi, J., Lim, S. Y., Lee, N., Kong, J. M., Hwang, Y. I., Kang, J. S., & Lee, W. J. (2013). Vitamin C Is an Essential Factor on the Anti-viral Immune Responses through the Production of Interferon-α/β at the Initial Stage of Influenza A Virus (H3N2) Infection. Immune network, 13(2), 70–74. https://doi.org/10.4110/in.2013.13.2.70
2. Padayatty SJ, Katz A, Wang Y, Eck P, Kwon O, Lee JH, Chen S, Corpe C, Dutta A, Dutta SK, Levine M. Vitamin C as an antioxidant: evaluation of its role indisease prevention. J Am Coll Nutr. 2003 Feb;22(1):18-35. Review. PubMed PMID:12569111.
3. Kaihatsu, K., Yamabe, M., & Ebara, Y. (2018). Antiviral Mechanism of Action of Epigallocatechin-3-O-gallate and Its Fatty Acid Esters. Molecules (Basel, Switzerland), 23(10), 2475. https://doi.org/10.3390/molecules23102475
4. Makela MJ, Puhakka T, Ruuskanen O, Leinonen M, Saikku P, Kimpimaki M, Blomqvist S, Hyypia T, Arstila P. Viruses and bacteria in the etiology of the common cold. J Clin Microbiol. 1998;36:539–542
5. Hulisz D. Efficacy of zinc against common cold viruses: an overview. J AmPharm Assoc (2003). 2004 Sep-Oct;44(5):594-603. Review. PubMed PMID: 15496046.
6. Wu, W., Li, R., Li, X., He, J., Jiang, S., Liu, S., & Yang, J. (2015). Quercetin as an Antiviral Agent Inhibits Influenza A Virus (IAV) Entry. Viruses, 8(1), 6. https://doi.org/10.3390/v8010006
7. Krawitz, C., Mraheil, M. A., Stein, M., Imirzalioglu, C., Domann, E., Pleschka, S., & Hain, T. (2011). Inhibitory activity of a standardized elderberry liquid extract against clinically-relevant human respiratory bacterial pathogens and influenza A and B viruses. BMC complementary and alternative medicine, 11, 16. https://doi.org/10.1186/1472-6882-11-16
8. Cascella R, Evangelisti E, Zampagni M, Becatti M, D’Adamio G, Goti A, LiguriG, Fiorillo C, Cecchi C. S-linolenoyl glutathione intake extends life-span and stress resistance via Sir-2.1 upregulation in Caenorhabditis elegans. Free Radic Biol Med. 2014 Aug;73:12735.doi:10.1016/j.freeradbiomed.2014.05.004. Epub 2014May 15. PubMed PMID: 24835770.
9. Millar AB, Pavia D, Agnew JE, Lopez-Vidriero MT, Lauque D, Clarke SW. Effect of oral N-acetylcysteine on mucus clearance. Br J Dis Chest. 1985;79(3):262–266.
10. Martineau AR, Jolliffe DA, Greenberg L, et al. Vitamin D supplementation to prevent acute respiratory infections: individual participant data meta-analysis. Health Technol Assess. 2019;23(2):1–44. doi:10.3310/hta23020
11. Chu, M., Xu, L., Zhang, M., Chu, Z., & Wang, Y. (2015). Role of Baicalin in Anti-Influenza Virus A as a Potent Inducer of IFN-Gamma. BioMed Research International, 2015, 1–11. doi:10.1155/2015/263630
12. Liao, L. Y., He, Y. F., Li, L., Meng, H., Dong, Y. M., Yi, F., & Xiao, P. G. (2018). A preliminary review of studies on adaptogens: comparison of their bioactivity in TCM with that of ginseng-like herbs used worldwide. Chinese medicine, 13, 57. https://doi.org/10.1186/s13020-018-0214-9
13. Mashhadi, N. S., Ghiasvand, R., Askari, G., Hariri, M., Darvishi, L., & Mofid, M. R. (2013). Anti-oxidative and anti-inflammatory effects of ginger in health and physical activity: review of current evidence. International journal of preventive medicine, 4(Suppl 1), S36–S42.
14. Catanzaro, M., Corsini, E., Rosini, M., Racchi, M., & Lanni, C. (2018). Immunomodulators Inspired by Nature: A Review on Curcumin and Echinacea. Molecules (Basel, Switzerland), 23(11), 2778. https://doi.org/10.3390/molecules23112778
15. Swamy, M. K., Akhtar, M. S., & Sinniah, U. R. (2016). Antimicrobial Properties of Plant Essential Oils against Human Pathogens and Their Mode of Action: An Updated Review. Evidence-based complementary and alternative medicine : eCAM, 2016, 3012462. https://doi.org/10.1155/2016/3012462
16. Hudson, J., & Vimalanathan, S. (2011). Echinacea—A Source of Potent Antivirals for Respiratory Virus Infections. Pharmaceuticals, 4(7), 1019–1031. https://doi.org/10.3390/ph4071019