Understanding the immune system and zinc
About the immune system
The immune system is acollection of cells, chemicals or processes. It protects the skin, respiratory tract, gastro-intestinal tract and other areas of the body against foreign bodies known as pathogens or antigens that may stimulate unwanted reactions or diseases. Protection happens against bacteria, fungi, viruses, parasites, cancer cells, toxins and so on.1
The immune system is classified into innate immunity and adaptive immunity.
Innate immune system
This is the first protective mechanism against infections, which is not antigen-specific and does not rely on immunological memory. This means that it does not have to recognise the antigen to fight against it, and it won’t “remember” the antigen in case it infects you again. The innate immune response is very rapid and can happen a few hours or immediately after invasion of the body by antigens.
There are four components of innate immunity:
- Anatomical barriers: the skin and mucous membranes (which line the inside of the mouth, nose and more) act as an external barrier to invading pathogens. This protects the body, tissues or cells from potential infections
- Chemical barriers: this is based on the changes in body physiology like acidic pH, temperature and chemical mediators in order to fight the invading antigen
- White blood cells: these include phagocytes (macrophages and neutrophils, which engulf and digest the pathogen), dendritic cells, natural killer cells, eosinophils, mast cells and basophils
- Inflammation: Damaged cells release inflammatory chemicals, which cause pain and fever and attract immune cells to remove or destroy the pathogen
Adaptive immunity
On the other hand, adaptive immunity is antigen-specific, and therefore takes days. First, the innate immune system presents the antigen to the adaptive immune system to find immune cells that “match” it, then these cells multiply to attack. However, the hallmark of adaptive immunity is that the body builds up an immunological memory, and quickly mounts a more efficient response to the antigen should you be exposed to the same antigen again in the future.
Adaptive immunity performs the following functions:
- Recognising specific non-self antigens (e.g. viruses and allergens)
- Distinguishing them from self antigens (your own cells)
- Generation of antigen-specific T cells, B cells and antibodies for the removal of the antigens or the antigen-infected cells
- Development of immunological memory that can quickly recognise and mount immune defense to the antigen should the body get exposed to it or similar pathogen again in the future1
This development of immunologic memory that recognises and mounts future attacks on invading pathogens is the basis of immunisation.
Innate and adaptive immunity work synergistically, hence a defect in one can lead to a number of diseases like inflammation, autoimmune disease, immunodeficiency and hypersensitivity.1
About zinc
Zinc is a micronutrient that plays a vital role in cell division, differentiation and proliferation. It helps in both growth and the immune system. Zinc is the second most abundant metal in the human body with about 2-4 grams in circulation.2 It is taken through food, water, breast milk and beverages, and the richest food sources of zinc include meat, fish and seafood.3 It is also available as over-the-counter dietary supplements, and some lozenges, denture adhesive creams and cold drinks. Zinc is widely distributed and absorbed through the zinc transporters in the intestine. The processes that maintain zinc balance/Homeostasis include absorption from diet/supplements, excretion in the gastrointestinal tract and reabsorption in the lumen.
The link between immune system and zinc
Effects of zinc in the immune system
Zinc deficiency has been linked to some forms of delayed growth and compromised immunity.2 This further buttresses the fact that zinc is an essential nutrient for growth and immune support. Zinc deficiency can result from malnutrition and disease conditions like diarrhea, dysentery and vomiting, which lead to the loss of essential micronutrients including zinc. The symptoms of this deficiency are different according to age; in children and infants, it manifests as diarrhea, while in adults, it increases infection susceptibility, alopecia and reduces growth.3
Zinc plays many roles in both innate and adaptive immunity. Zinc deficiency depresses the activity of neutrophils and natural killer cells, and affects macrophages by reducing phagocytosis, production of cytokines (which immune cells use to communicate), and their ability to kill engulfed pathogens. In the adaptive immune system, it prevents cell multiplication, cytokine production and antibody release of T and B cells, and causes atrophy of the thymus gland, where T cells develop.2 The consequence of zinc deficiency is likely the reduction of cellular functions like gene replication, cell division and survival, leaving people more vulnerable to infections and finding them harder to shake off.2
FAQs
How much and how often should I take zinc?
The total amount of zinc in the body differs both by sex and age. For females, the total is around 1.5g, while for males, the total is 2.5g, and it is stored in skeletal muscles and bone.3 As the amount of zinc taken increases, the overall absorption increases, but a smaller proportion of your intake is absorbed.3 Serum and plasma zinc status are important parameters in assessing the zinc level in the body. A serum zinc level of 80-120 mcg/dl is normal for healthy people. A serum zinc level of 70 mcg/dl or less for people assigned female at birth, and 74 mcg/dl or less for people assigned male at birth has clinical implications as it indicates zinc deficiency.3 It is also worthy to note that zinc concentration level in the serum is related to the time of taking the blood sample; either morning or evening. It also changesas a result of muscle wasting, infections, or hormone fluctuations.3
The table below shows the average daily intake requirements of zinc across age group, sex and physiological condition.
| Age | Male | Female | Pregnancy | Lactation |
| Birth to 6 months* | 2 mg | 2 mg | ||
| 7–12 months | 3 mg | 3 mg | ||
| 1–3 years | 3 mg | 3 mg | ||
| 4–8 years | 5 mg | 5 mg | ||
| 9–13 years | 8 mg | 8 mg | ||
| 14–18 years | 11 mg | 9 mg | 12 mg | 13 mg |
| 19+ years | 11 mg | 8 mg | 11 mg | 12 mg |
Source: NIH, Office of Dietary Supplements.3
What are the side effects of taking zinc?
Taking zinc orally can cause the following symptoms: headaches, diarrhea, nausea, vomiting and indigestion.
Summary
Zinc is an essential micronutrient that plays an important role in maintaining strong immunity, and is vital in cell growth and differentiation, wound healing, general growth and balance in both children and adults. Zinc is important in both innate and adaptive immunity. Zinc sources range from dietary intake, supplements, creams, over-the-counter medicines and so on. The daily zinc requirements in the body differs from age to age and also from sex. Zinc deficiency manifests in children and infants as diarrhoea while in adults, it results in reduced growth, decreased wound healing, and increased susceptibility to infections.
References
- Marshall JS, Warrington R, Watson W, Kim HL. An introduction to immunology and immunopathology. Allergy, Asthma & Clinical Immunology. 2018 Sep 12;14(2):49. Available from: https://doi.org/10.1186/s13223-018-0278-
- Hojyo S, Fukada T. Roles of zinc signaling in the immune system. Journal of Immunology Research [Internet]. 2016 Oct 31;2016:e6762343. Available from: https://www.hindawi.com/journals/jir/2016/6762343/
- Office of dietary supplements - zinc [Internet]. [cited 2022 Dec 8]. Available from: https://ods.od.nih.gov/factsheets/Zinc-HealthProfessional/
