6 Supplements to Boost Your Immune System

Immune system functioning is something that is often taken for granted. Even when one is not feeling sick, the immune system is working every hour of every day by neutralising cancerous growth, clearing wastes from the body, and fighting developing infections[1]. Certain supplements have the potential to provide a boost to your immune system function for fighting off illnesses caused by infections and for supporting general well-being.


zincThe beneficial effects of zinc for symptoms of the common cold were first documented 30 years ago[2]. Since then, a modest body of literature has formed which supports the efficacy of zinc as a mild palliative aid for cold symptoms. Prophylactic administration of zinc (to prevent cold) has not been substantiated[3]. Further studies are needed as the current data are not fully conclusive.

Zinc modulates various components of both the innate (e.g. neutrophils, macrophages)[4] and adaptive (e.g. B- & T-lymphs)[5][6] immune systems.


A 2015 Cochrane review of 16 therapeutic trials (n = 1387) found that administration within 24h of cold onset at a dose of over 75 mg per day had the following effects[7]:

  • Zinc significantly reduced the duration of cold symptoms by a mean difference of -1.03 days
  • Zinc had no effect on the severity of cold symptoms.
  • Individuals who took zinc were about half as likely to be symptomatic after 7 days of treatment, were less likely to develop a cold, less likely to be absent from school, and were less likely to be prescribed antibiotics (note: although antibiotics should not be prescribed for the common cold as it is caused by a virus, they are nevertheless frequently given due to patient insistence.).

Although the authors noted high heterogeneity within the data, these data appear to corroborate general findings from the literature. Zinc appears to be mildly effective for reducing symptoms of the common cold.


Zinc is available in many salt forms. The most common over-the-counter formulations are zinc oxide, zinc acetate, and zinc gluconate[8]. Other formulations vary in bioavailability, with zinc monomethionine being the most absorbed. The amount of ionic zinc content seems to be correlated to therapeutic efficacy[9], however, the acetate and gluconate salts have been most studied.

The usual dosage ranges from 4.5 to 24 mg of elemental zinc taken every 1 to 2 hours during waking hours as cold symptoms persist[10]. The regimen is typically continued for 5 to 14 days or until symptoms subside.


High doses (≥100 mg) of or prolonged exposure (≥10 years) to zinc may be unsafe[11], and has been linked to adverse sequelae such as prostate cancer. Be aware of elemental zinc content in multivitamins. Pregnant or breastfeeding women should limit their zinc intake to less than 40 mg/day.

As a caution, zinc may interfere with the absorption of certain drugs[12], such as quinolone and tetracycline antibiotics, as well as other mineral supplements, such as calcium or iron. Notify your doctor and pharmacist if you are taking zinc. Zinc should be taken 2 hours before or 6 hours after quinolone & tetracycline antibiotics.

Side effects are relatively mild and limited. Bad taste and nausea are frequently reported[13].

There is a concern that doses higher than 40 mg per day may interfere with copper absorption, leading to anaemia[14]. One study has tested the effects of long-term coadminstration of zinc & copper; through 6 years of supplementation no significant adverse effects were reported[15].


garlicGarlic is a culinary herb that has been largely investigated for its benefits on cardiovascular health, which stem from modest reductions in blood pressure and cholesterol levels[16]. In addition to these helpful effects, garlic may also have an immunostimulating effect.

The active constituent in garlic is a compound called allicin, which has been shown to promote the activity of various components of the immune system, evidenced by enhanced phagocytosis, lymphocyte proliferation, and inhibition of immunosuppressive processes, among other mechanisms. Allicin has also demonstrated intrinsic antimicrobial activity demonstrated in vitro.

Formulations & Dosage

Garlic can be consumed in a variety of forms. In general, the recommended allicin intake is 2 to 5 mg per day[17]. The following dosages approximate this amount. Be advised that various formulations may vary in allicin content and pharmacologic properties [18]. Further information about various formulations and intake can be found here.

  • 2 to 5 g of fresh garlic (cut, not crushed & uncooked[19])
  • 0.4 to 1.2 g of dried powder
  • 2 to 5 mg of oil
  • 300 to 1000 mg of extract


Increased garlic intake should be avoided in individuals with a bleeding disorder (e.g. haemophilia or other coagulopathy) or planned surgery within 2 weeks[20]. Because allicin has been shown to inhibit platelet aggregation and TxA2 synthesis, individuals consuming large amounts of garlic are at an increased bleeding risk. Exercise caution if you are taking «blood thinners» such as warfarin or aspirin and consult your doctor and pharmacist before use.

Individuals with diabetes, GI infection, and inflammatory bowel disease should also exercise caution[21].

Allicin has been observed to substantially inhibit the CYP2E1 isozyme, reducing its activity by up to 39%[22]. Consequently, elevations in drugs metabolised by 2E1 may be expected. These include paracetamol and alcohol.

As an inducer of the CYP3A4 isozyme[23], an increased consumption of garlic may stimulate the metabolism of certain drugs including birth control.

Adverse Effects

Gastrointestinal upset is the most common complaint with supplemental garlic consumption[24]. This entails heartburn, intestinal gas and bloating, nausea and vomiting, and diarrhoea. A tolerance may develop to these side effects over time. Certain extracts may be associated with less gastrointestinal upset.

Reishi Mushroom

ganoderma lucidum

The Reishi mushroom is a fungal remedy which has been used in traditional Chinese medicine. Its major studied properties include antioxidant, antineoplastic, and immunomodulatory activity[25].

Its pharmacologic effects derive from many bioactive molecules, which include various polysaccharides and triterpenes, among others. Polysaccharides seem to be involved in modulating the immune system[26], which entails stimulating the proliferation and differentiation of T-lymphocytes & NK cells, for example, when the immune system is weakened, and attenuating TNFα and some interleukin activity when the immune system is over-functioning (e.g. auto-immune disease).


This supplement should be avoided in individuals with an autoimmune disease (e.g. multiple sclerosis) or immunosuppression therapy (e.g. for transplant recipients)[27]. Ganoderma‘s immunomodulating effects may trigger disease flares or organ rejection.

Use within 2 weeks of surgery is also not recommended as with garlic extracts[28]. Some constituents in Ganoderma inhibit platelet aggregation, producing a clinically significant effect at doses over 3 grams per day. Thus, individuals taking Ganoderma may be at a higher risk of bleeding.

Ganoderma may interact with certain medications for diabetes and blood pressure by contributing to their effects[29]. In individuals receiving antidiabetics such as insulin or glipizide, supplementing Ganoderma may increase the risk of hypoglycaemia, or dangerously low blood sugar which may lead to a seizure. Individuals taking medications for blood pressure, such as lisinopril, may be at a higher risk of hypotension, or very low blood pressure which may lead to shock.

Adverse Effects

The most frequently reported side effects with Ganoderma supplementation are bleeding[30], rash, dizziness, and headache.

Lion’s Mane Mushroom

lion's maneHericium is another medicinal fungus used in traditional Chinese therapeutics as well as in cuisine. It is named for its characteristic spines. H. erinaceus has been observed to produce various beneficial effects when consumed, ranging from enhancement of metabolic processes (such as fat metabolism)[31] to neurogenesis[32], to name a few.

Hericium erinaceus preparations contain molecules which may stimulate or suppress elements of the immune system[33]. Polysaccharides have been observed to promote macrophage activity while some other components of Lion’s mane preparations have been shown to inhibit chemotaxis[34].

Lion’s mane is available as powdered mushroom or the more potent powdered extract (in different strengths, e.g. 10:1 extract with 30% polysaccharide content). The typical dosage is as follows: 1 g of the purified extract by mouth three times a day with food[35]. As with all of these supplements, a lower starting dosage with a scheduled titration may be considered.

Adverse Effects

Hericium may cause itching. If this occurs without signs and symptoms of an allergic reaction such as hives, it is most likely due to nerve sensitivity in the setting of elevated Nerve Growth Factor (NGF)[36]. The long-term safety of Hericium is uncharacterised.

Vitamin C

vitamin c

This water-soluble vitamin has been traditionally recommended as an immune system booster specifically with regard to the common cold[37]. However, the data are highly conflictive as to whether supplementing vitamin C actually helps[38].

Vitamin C is purported to support the immune system through its function as an antioxidant, protecting host cells from oxidative stress caused by pathogens.

Stronger evidence supports the use of vitamin C to marginally reduce the duration of cold symptoms by approximately 1 to 1.5 days. A 2013 Cochrane meta-analysis found in 24 trials that studied the general population, supplementing vitamin C did not significantly reduce the risk of developing a cold (RR 0.97, 95% CI 0.94–1.00)[39]. The same meta-analysis found that regular vitamin C supplementation could modestly reduce the duration and the severity of cold symptoms. Adults experienced an 8% reduction (3–12%) and children a 14% reduction (7-21%).

Formulations & Dosage

While vitamin C is better absorbed at lower doses, it appears that higher doses are required to achieve benefit. A dosage of 1–3 g by mouth daily is recommended starting at the onset of symptoms & continued up to 3-5 days or as long as symptoms persist[40].

Labdoor has published rankings for the best vitamin C formulations.


Individuals with G6PD deficiency should exercise caution with higher doses of vitamin C, as there is a risk of precipitating haemolytic anaemia[41].

Vitamin C is generally well-tolerated[42]. At high doses, however, adverse effects may present themselves. These include gastrointestinal upset marked by nausea, vomiting and diarrhoea and flushing of the skin.


colostrumColostrum is a rich pre-milk fluid derived from cows during the first 2–4 days after birth. This substance contains immune factors, amino acids, minerals, and other nutrients which promote the growth of the offspring[43]. Nutrients from colostrum support general metabolic functioning while other compounds may have intrinsic antimicrobial activity. Colostrum in particular provides a substantial amount of secretory immunoglobulin A (IgA), which is an antibody involved in the humoral immune response[44].

It is debatable whether adults would benefit from consumption of colostrum as much as newborns[45]. Newborns have a relatively undeveloped gastrointestinal system which does not degrade food intake to the extent that a fully developed gastrointestinal system would. An adult’s stomach would more likely break down many of the helpful constituents present in colostrum. Colostrum has been used to prevent some gastrointestinal infections in children, such as infectious diarrhoea & gastroenteritis. It may also be effective in preventing these infections in immunocompromised patients, such as individuals with AIDS. However, the efficacy of colostrum as an immune system booster in the healthy adult population has not been substantiated.


Because colostrum is a dairy product, it is not recommended for individuals with lactose intolerance or dairy allergy.

Heat-denatured bovine immunoglobulin present in colostrum may contribute to atherosclerotic processes[46]. Patients with high cholesterol should discuss with their doctor or pharmacist before use.

Colostrum is generally well-tolerated. The most common side effects experienced with colostrum are gastrointestinal in nature, such as nausea, vomiting, diarrhea, intestinal gas, and bloating.


There are many different ways to augment your immune system, reducing your risk of becoming sick & attenuating symptoms of being sick. Before starting any substance, research how it works, how to take it (e.g. when to start, how much, when to stop, etc.), and any warnings (e.g. colostrum should not be tried in individuals with a dairy allergy). Stay safe!

References   [ + ]

1. Owen JA, Punt J, Stranford SA. Immunology. 7th ed. New York: W.H. Freeman & Company; c2013. Chapter 1, Overview of the Immune System.
2. Eby GA, Davis DR, Halcomb WW. Reduction in duration of common colds by zinc gluconate lozenges in a double-blind study. Antimicrobial Agents & Chemotherapy 1984;25:20-4.
3, 10, 11, 14. Zinc. Natural Medicines®. Therapeutic Research Center, Somerville, Massachusetts, USA. [updated 17 Jun 2015].
4. Sheikh A, Shamsuzzaman S, Ahmad SM, Nasrin D, Nahar S, Alam MM, Al Tarique A, Begum YA, Qadri SS, Chowdhury MI, Saha A, Larson CP, & Qadri F. Zinc influences innate immune responses in children with enterotoxigenic Escherichia coli-induced diarrhea. J Nutr 2010;140(5):1049-1056.
5. Licastro F, Chiricolo M, Mocchegiani E, et al. Oral zinc supplementation in Down’s syndrome subjects decreased infections & normalized some humoral & cellular immune parameters. J Intellect Disabil Res 1994;38:149-62.
6. Stabile A, Pesaresi MA, Stabile, AM, Pastore M, Sopo SM, Ricci R, Celestini E, & Segni G. Immunodeficiency & plasma zinc levels in children with Down’s syndrome: a long-term follow-up of oral zinc supplementation. Clin Immunol.Immunopathol. 1991;58(2):207-216.
7. Singh M, Das RR. Zinc for the common cold. Cochrane Database of Systematic Reviews 2013, Issue 6. Art. No.: CD001364. DOI: 10.1002/14651858.CD001364.pub4.
8. DiSilvestro RA. Handbook of Minerals as Nutritional Supplements. CRC Press: Boca Raton, Florida; 2004.
9. Eby GA. Zinc lozenges as cure for the common cold– a review and hypothesis. Med Hypotheses. 2010 Mar;74(3):482-92.
12, 13. Micromedex® 1.0 (Healthcare Series), (electronic version). Truven Health Analytics, Greenwood Village, Colorado, USA. Available at:
15. Age-Related Eye Disease Study Research Group. The effect of five-year zinc supplementation on serum zinc, serum cholesterol and hematocrit in persons randomly assigned to treatment group in the age-related eye disease study: AREDS Report No. 7. J Nutr. 2002 Apr;132(4):697-702.
16, 20, 21, 24. Garlic. Natural Medicines®. Therapeutic Research Center, Somerville, Massachusetts, USA. [updated 14 Feb 2015].
17. World Health Organisation. Monographs on Selected Medicinal Plants, Volume I. Geneva: WHO; 1999.
18. Kasuga S, Uda N, Kyo E, Ushijima M, Morihara N, & Itakura Y. Pharmacologic activities of aged garlic extract in comparison with other garlic preparations. J Nutr 2001;131(3s):1080S-1084S.
19. Song K & Milner JA. The influence of heating on the anticancer properties of garlic. J Nutr 2001;131(3s):1054S-1057S.
22. Gurley BJ, Gardner SF, Hubbard MA, et al. Cytochrome P450 phenotypic ratios for predicting herb-drug interactions in humans. Clin Pharmacol Ther 2002;72:276-87.
23. Piscitelli SC, Burstein AH, Welden N, et al. The effect of garlic supplements on the pharmacokinetics of saquinavir. Clin Infect Dis 2002;34:234-8.
25, 27, 28. Reishi Mushroom. Natural Medicines®. Therapeutic Research Center, Somerville, Massachusetts, USA. [updated 16 Feb 2015].
26. Xu Z, Chen X, Zhong Z, Chen L, & Wang Y. Ganoderma lucidum polysaccharides: immunomodulation & potential anti-tumor activities. Am.J.Chin Med. 2011;39(1):15-27.
29. Gao Y, Lan J, Dai X, Ye J, & Zhou S. A Phase I/II Study of Ling Zhi Mushroom.
30. Tao J & Feng KY. Experimental & clinical studies on inhibitory effect of ganoderma lucidum on platelet aggregation. J Tongji Med Univ 1990;10:240-3.
31. Hiwatashi K, Kosaka Y, Suzuki N, Hata K, Mukaiyama T, Sakamoto K, et al. Yamabushitake mushroom (Hericium erinaceus) improved lipid metabolism in mice fed a high-fat diet. Biosci Biotechnol Biochem. 2010;74(7):1447-51.
32. Wong KH, Naidu M, David RP, Bakar R, Sabaratnam V. Neuroregenerative potential of lion’s mane mushroom, Hericium erinaceus (Bull.: Fr.) Pers. (higher Basidiomycetes), in the treatment of peripheral nerve injury (review). Int J Med Mushrooms. 2012;14(5):427-46.
33. Kim YO, Lee SW, Oh CH, Rhee YH. Hericium erinaceus suppresses LPS-induced pro-inflammation gene activation in RAW264.7 macrophages. Immunopharmacol Immunotoxicol. 2012 Jun;34(3):504-12.
34. Abdulla MA, Fard AA, Sabaratnam V, Wong KH, Kuppusamy UR, Abdullah N, et al. Potential activity of aqueous extract of culinary-medicinal Lion’s Mane mushroom, Hericium erinaceus (Bull.: Fr.) Pers. (Aphyllophoromycetideae) in accelerating wound healing in rats. Int J Med Mushrooms. 2011;13(1):33-9.
35. Mori K, Inatomi S, Ouchi K, Azumi Y, Tuchida T. Improving effects of the mushroom Yamabushitake (Hericium erinaceus) on mild cognitive impairment: a double-blind placebo-controlled clinical trial. Phytother Res. 2009 Mar;23(3):367-72.
36. Tanaka A, Matsuda H. Expression of nerve growth factor in itchy skins of atopic NC/NgaTnd mice. J Vet Med Sci. 2005 Sep;67(9):915-9.
37, 40, 41, 42. Vitamin C. Natural Medicines®. Therapeutic Research Center, Somerville, Massachusetts, USA. [updated 17 Mar 2015].
38, 39. Hemilä H, Chalker E. Vitamin C for preventing & treating the common cold. Cochrane Database of Systematic Reviews 2013, Issue 1. Art. No.: CD000980. DOI: 10.1002/14651858.CD000980.pub4.
43. Thapa, BR. Health factors in colostrum. Indian J Pediatr 2005;72(7):579-581.
44. He F, Tuomola E, Arvilommi H, Salminen S. Modulation of human humoral immune response through orally administered bovine colostrum. FEMS Immunol Med Microbiol. 2001 Aug;31(2):93-6.
45. Bovine Colostrum. Natural Medicines®. Therapeutic Research Center, Somerville, Massachusetts, USA. [updated 14 Feb 2015].
46. Annand, JC. Denatured bovine immunoglobulin pathogenic in atherosclerosis. Atherosclerosis 1986;59(3):347-351.