Immunity tends to refer to the capacity of the body to ward off infections, and tends to be measured acutely by seeing the count or activity of immune cells that can help ward off sickness. Enhanced immunity results in less sickness.

Our evidence-based analysis features 21 unique references to scientific papers.

Research analysis by and verified by the Research Team. Last updated on Apr 29, 2017.

Summary of Immunity

Primary Information, Benefits, Effects, and Important Facts

Immunity refers to the body's innate ability to fight off diseases. The immune system does this by fighting off pathogens, which can range from molecules to parasites. In order to do this, there are two main levels to immunity.

The first level is called the the innate immune system. This provides a quick first line of defense, and acts against a wide range of pathogens. The innate immune system is comprised in part by physical barriers such as the skin, nonspecific chemical defenses such as lysozyme (an enzyme secreted in various secretions such as tears and saliva that breaks down bacterial cell walls), and the normal flora, which are nonpathogenic bacteria that compete for space and resources with pathogenic bacteria. If a pathogen circumvents these defenses, it will then face the inflammatory response which can attract immune cells to the site of infection and dilate blood vessels to help ferry them there. Interferons can also be released which help fight viruses and tumors, and the complement system can attack the cell membranes of pathogens either disrupting them or promoting their elimination by other components of the immune system. Finally, various cells of the innate immune system can be activated. Phagocytic cells can engulf invading pathogens and destroy them upon ingestion, while natural killer cells can kill cells infected with a virus and tumor cells, and eosinophils can produce and release substances that are effective against parasites.

The second main level of immunty is called the adaptive immune system. This level takes time before responding to a pathogenic invasion, but once mobilized, it evokes a response specific to a particular pathogen, as opposed to the innate immune system, whose response is nonspecific. The adaptive immune system is also capable of remembering a specific pathogen, so that it can mount a more rapid, effective response to a pathogen which it has encounterd before. This is the basis of how vaccines work. The adaptive immune system is comprised of two main cell types: T cells (named because they were found in the thymus, the organ which they mature) and B cells (named for the bone marrow, where they are initially produced). Both kinds of cells are antigen-specific and are activated when they recognize an antigen of a pathogen. The two major types of T cells are killer or cytotoxic T cells and helper T cells. The former kill cells that are infected with viruses or cancer cells. They are also called CD8+ cells, since they have a co-receptor on their surface called CD8 that helps them recognize specific antigens. The latter help mount an immune response to a specific antigen in a multitude of ways, including the release of cytokines which help regulate parts of the immune system, and can mature into memory cells (which help remember a specific antigen) and regulatory cells (sometimes called Tregs for short, which help downregulate the immune response). Helper T cells are also called CD4+ due the the CD4 co-receptor on their surface. B cells make antigen-specific antibodies which can attach to pathogens and activate the compliment system more specifically, help phagocytes engulf the pathogen, or neutralize the pathogen by coating it.

Frequently Asked Questions

Questions and answers regarding Immunity

Q: Which supplements for the cold and flu?

A: Eating well, sleeping well, and minimizing stress are still the best ways to ward off cold and flu, but the evidence suggests that some supplements can also help.

Read full answer to "Which supplements for the cold and flu?"

Human Effect Matrix

The Human Effect Matrix looks at human studies (it excludes animal and in vitro studies) to tell you what supplements affect immunity

Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
Vitamin E
All comparative evidence is now gathered in our ​A-to-Z Supplement Reference.
The evidence for each separate supplement is still freely available ​here.
Astragalus membranaceus  
Eleutherococcus senticosus  
Ganoderma lucidum  
Holy Basil  
Lactobacillus casei  
Lactobacillus reuteri  
Nigella sativa  

Scientific Support & Reference Citations

Via HEM and FAQ:

  1. Shah SA, et al. Evaluation of echinacea for the prevention and treatment of the common cold: a meta-analysis. Lancet Infect Dis. (2007)
  2. Karsch-Völk M, et al. Echinacea for preventing and treating the common cold. Cochrane Database Syst Rev. (2014)
  3. Tiralongo E, Wee SS, Lea RA. Elderberry Supplementation Reduces Cold Duration and Symptoms in Air-Travellers: A Randomized, Double-Blind Placebo-Controlled Clinical Trial. Nutrients. (2016)
  4. Ulbricht C, et al. An evidence-based systematic review of elderberry and elderflower (Sambucus nigra) by the Natural Standard Research Collaboration. J Diet Suppl. (2014)
  5. Holst L, Havnen GC, Nordeng H. Echinacea and elderberry-should they be used against upper respiratory tract infections during pregnancy?. Front Pharmacol. (2014)
  6. Parry-Billings M, et al. Plasma amino acid concentrations in the overtraining syndrome: possible effects on the immune system. Med Sci Sports Exerc. (1992)
  7. Fashner J, Ericson K, Werner S. Treatment of the common cold in children and adults. Am Fam Physician. (2012)
  8. Lizogub VG, Riley DS, Heger M. Efficacy of a pelargonium sidoides preparation in patients with the common cold: a randomized, double blind, placebo-controlled clinical trial. Explore (NY). (2007)
  9. Meng H, et al. Consumption of Bifidobacterium animalis subsp. lactis BB-12 impacts upper respiratory tract infection and the function of NK and T cells in healthy adults. Mol Nutr Food Res. (2016)
  10. Braga VL, et al. What do Cochrane systematic reviews say about probiotics as preventive interventions?. Sao Paulo Med J. (2017)
  11. Strasser B, et al. Probiotic Supplements Beneficially Affect Tryptophan-Kynurenine Metabolism and Reduce the Incidence of Upper Respiratory Tract Infections in Trained Athletes: A Randomized, Double-Blinded, Placebo-Controlled Trial. Nutrients. (2016)
  12. Wang Y, et al. Probiotics for prevention and treatment of respiratory tract infections in children: A systematic review and meta-analysis of randomized controlled trials. Medicine (Baltimore). (2016)
  13. Pu F, et al. Yogurt supplemented with probiotics can protect the healthy elderly from respiratory infections: A randomized controlled open-label trial. Clin Interv Aging. (2017)
  14. Carr AC, Maggini S. Vitamin C and Immune Function. Nutrients. (2017)
  15. Hemilä H. Vitamin C and Infections. Nutrients. (2017)
  16. Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. (2013)
  17. Autier P, et al. Effect of vitamin D supplementation on non-skeletal disorders: a systematic review of meta-analyses and randomised trials. Lancet Diabetes Endocrinol. (2017)
  18. Aglipay M, et al. Effect of High-Dose vs Standard-Dose Wintertime Vitamin D Supplementation on Viral Upper Respiratory Tract Infections in Young Healthy Children. JAMA. (2017)
  19. Singh M, Das RR. Zinc for the common cold. Cochrane Database Syst Rev. (2013)
  20. Hemilä H. Zinc lozenges and the common cold: a meta-analysis comparing zinc acetate and zinc gluconate, and the role of zinc dosage. JRSM Open. (2017)
  21. Alexander TH, Davidson TM. Intranasal zinc and anosmia: the zinc-induced anosmia syndrome. Laryngoscope. (2006)

Cite this page

"Immunity,", published on 20 May 2014, last updated on 29 April 2017,