The immune system is not a single organ or a simple on/off switch. It is a layered, interdependent network of physical barriers, innate responders, and adaptive mechanisms that has taken evolutionary biology millions of years to refine. When people ask me how to "support" it, I find the question simultaneously reasonable and underspecified — because the answer depends entirely on which layer you are talking about, what your current nutritional status looks like, and whether the intervention in question has been tested in humans rather than cell cultures.
This guide covers the evidence base for the micronutrients and compounds most relevant to immune defence: what the research actually shows, where it is strong, where it is genuinely limited, and how the ingredients in KōJō Daily Formula v4.1 map onto the biology. I have tried to be precise about effect sizes and study populations, because a meta-analysis in selenium-deficient elderly patients tells you something quite different from a trial in well-nourished athletes. The distinction matters if you are a 30-something professional eating a varied diet and wondering whether any of this applies to you.
The short answer is: several micronutrients have robust mechanistic and clinical evidence; the gut-immune axis is real and increasingly well-characterised; and the combination of adequate vitamin D, vitamin C, zinc, and selenium — alongside a functioning gut microbiome — represents the most evidence-supported nutritional foundation for immune competence currently available.
The Architecture of Immune Defence: What You Are Actually Supporting
Before discussing nutrients, it is worth being precise about what "immune defence" means structurally. The system operates in three broad layers.
Physical and chemical barriers — skin, mucous membranes, cilia, gastric acid, and antimicrobial peptides — constitute the first line. These are not glamorous, but they are the reason the vast majority of pathogens never reach the bloodstream. Vitamin C is directly relevant here: it contributes to the synthesis of collagen, which underpins epithelial integrity, and it supports the function of neutrophils that patrol mucosal surfaces. Carr 2018
Innate immunity responds within minutes to hours. Pattern-recognition receptors on macrophages and dendritic cells identify conserved pathogen signatures, triggering inflammation, phagocytosis, and the release of cytokines. This system is fast but non-specific. Zinc plays a particularly well-characterised role here: zinc ions regulate intracellular signalling in macrophages and natural killer cells, and zinc deficiency is associated with impaired innate responses. Wessels 2018
Adaptive immunity — T cells, B cells, antibody production, and immunological memory — takes days to weeks to mount but is highly specific and forms the basis of long-term protection. Vitamin D receptors are expressed on virtually every immune cell type involved in this layer, and the evidence for vitamin D's regulatory role in adaptive immunity is now substantial. Johnson 2024
Understanding this architecture matters because no single nutrient "supports the immune system" in a monolithic sense. Different compounds act at different layers, and deficiency in any one of them creates a specific vulnerability rather than a general weakening.
Vitamin D: The Immune Regulator With the Strongest Evidence Base
If I had to identify one micronutrient where the mechanistic evidence, the observational data, and the intervention trials converge most convincingly, it would be vitamin D — with the important caveat that much of the benefit appears to accrue specifically to those who are deficient, which in the UK is a substantial proportion of the population.
Vitamin D is not strictly a vitamin. It is a steroid hormone precursor, and its active form — 1,25-dihydroxyvitamin D₃ — binds to nuclear receptors present on T cells, B cells, macrophages, and dendritic cells. This is not a peripheral role. The receptor is there because vitamin D directly regulates the transcription of genes involved in immune activation, tolerance, and antimicrobial peptide production. Bikle 2022
Mechanistically, vitamin D promotes the differentiation of monocytes into macrophages, induces the production of cathelicidin (an antimicrobial peptide), and modulates the Th1/Th2 balance in adaptive immunity — reducing the risk of excessive inflammatory responses while maintaining pathogen clearance capacity. Zughaier 2021 The cytokine storm phenomenon observed in severe respiratory infections — where immune overactivation causes more damage than the pathogen itself — is one context in which vitamin D's regulatory role has attracted significant research attention. Bikle 2022
Observational data consistently show an inverse relationship between vitamin D status and susceptibility to respiratory infections and autoimmune conditions. Johnson 2024 The challenge with observational data is confounding — people with higher vitamin D levels may also have more outdoor activity, better diets, and higher socioeconomic status, all of which independently affect immune function. Intervention trials are therefore the more reliable source.
The intervention evidence is broadly positive for deficient populations, more equivocal for those already replete. This is not surprising: correcting a deficiency restores function; supplementing beyond adequacy does not necessarily add further benefit.
EFSA's NHC register approves the wording "Vitamin D contributes to the normal function of the immune system" — a claim grounded in the mechanistic and clinical evidence base.
Vitamin C: Pleiotropic Functions Across the Immune Spectrum
Vitamin C occupies an unusual position in the evidence landscape. It is one of the most studied micronutrients in immunology, the mechanistic data are genuinely impressive, and yet the clinical evidence for supplementation in already-replete individuals is more modest than popular accounts suggest. The nuance is worth unpacking.
Mechanistically, vitamin C is a potent electron donor — an antioxidant that protects immune cells from the oxidative environment they create when destroying pathogens. Neutrophils, which are among the most active phagocytic cells in the innate immune system, accumulate vitamin C at concentrations up to 50 times higher than plasma levels. This concentration gradient suggests the cell is actively sequestering the nutrient for functional purposes. Carr 2018
Beyond antioxidant protection, vitamin C is a cofactor for enzymes involved in collagen synthesis — directly relevant to the integrity of epithelial barriers — and it supports the proliferation and differentiation of T and B lymphocytes in adaptive immunity. It also promotes the production of interferons, the signalling proteins that alert neighbouring cells to viral infection. Cerullo 2020
The clinical picture is more complex. Supplementation in the general population does not appear to prevent the common cold, though it may modestly reduce duration and severity. In populations under significant physical stress — marathon runners, soldiers in sub-arctic conditions — prophylactic supplementation does appear to reduce incidence, suggesting that high physiological demand depletes vitamin C reserves to a point where supplementation becomes relevant. Carr 2018
In cancer patients undergoing chemotherapy, where vitamin C depletion is frequently documented, supplementation has been studied as a means of supporting immune cell function, though the evidence remains preliminary. van 2019
EFSA's NHC register approves the wording "Vitamin C contributes to the normal function of the immune system."
Zinc: The Gatekeeper of Immune Signalling
Zinc is perhaps the most mechanistically well-characterised immune micronutrient after vitamin D. The evidence accumulated over the past four decades is substantial, and the language used in one of the field's most-cited reviews — "gatekeeper of immune function" — is not hyperbole. Wessels 2018
Zinc ions act as second messengers in immune cell signalling. They regulate the activity of over 300 enzymes and are involved in the transcription of genes governing inflammation, apoptosis, and immune cell development. The thymus — the organ responsible for T cell maturation — is particularly sensitive to zinc status; zinc deficiency causes thymic atrophy and impairs the production of thymulin, a zinc-dependent hormone required for T cell differentiation.
At the cellular level, zinc is required for the function of natural killer cells, the proliferation of T lymphocytes, and the production of cytokines including interleukin-2 and interferon-gamma. It also has a direct antiviral role: zinc ions inhibit the replication of certain RNA viruses by interfering with viral RNA-dependent RNA polymerase. Bonaventura 2015
Zinc deficiency is more common than most people assume. It does not always manifest as overt clinical deficiency — marginal zinc insufficiency, particularly in older adults, vegetarians, and those with high dietary phytate intake, is associated with measurable impairments in immune function without obvious symptoms. Wessels 2018
The form of zinc matters. Zinc bisglycinate — the form used in KōJō Daily Formula — is a chelated form with superior bioavailability compared to zinc oxide or zinc sulphate, which is relevant because the absolute dose is only one part of the equation; how much is absorbed is the other.
EFSA's NHC register approves the wording "Zinc contributes to the normal function of the immune system."
Selenium: Selenoproteins, Oxidative Stress, and Immune Competence
Selenium is an essential trace element whose immune functions are mediated almost entirely through selenoproteins — a family of over 30 proteins that incorporate selenocysteine at their active sites. The most immunologically relevant of these are the glutathione peroxidases (GPXs), which protect immune cells from oxidative damage, and thioredoxin reductases, which regulate redox signalling in lymphocytes. Bai 2025
The immune system is particularly vulnerable to oxidative stress because activated immune cells deliberately generate reactive oxygen species to destroy pathogens — a process that, if inadequately controlled, damages the immune cells themselves. Selenium-dependent GPXs are central to managing this oxidative burden. Avery 2019
Beyond antioxidant protection, selenium influences the proliferation and differentiation of T cells, the cytotoxic activity of natural killer cells, and the inflammatory response. Low selenium status is associated with impaired antibody responses to vaccination and increased susceptibility to viral infections — including evidence that selenium deficiency may increase the rate at which RNA viruses mutate to more virulent forms. Razaghi 2021
A systematic review and meta-analysis of experimental human studies found that selenium supplementation in selenium-deficient individuals produced measurable improvements in immune function markers, though the evidence in replete populations was less consistent. Filippini 2023 This mirrors the pattern seen with vitamin D and zinc: correcting deficiency restores function; the marginal benefit of supplementation in already-adequate individuals is smaller and less reliably demonstrated.
UK soil selenium levels are notably low compared to North American soils, and UK dietary selenium intake is frequently below recommended levels — making this a more relevant consideration for a UK audience than it might be elsewhere.
EFSA's NHC register approves the wording "Selenium contributes to the normal function of the immune system."
The Gut-Immune Axis: Why the Microbiome Is Central to Immune Defence
Approximately 70% of the body's immune tissue is located in or adjacent to the gastrointestinal tract. This is not coincidental. The gut is the site of the largest and most continuous exposure to foreign antigens — dietary proteins, commensal bacteria, and pathogens — and the immune system must constantly discriminate between what to tolerate and what to attack. The gut microbiome is integral to this process.
The mechanisms are multiple. Commensal bacteria produce short-chain fatty acids (SCFAs) — particularly butyrate — that directly influence the differentiation of regulatory T cells, the immune cells responsible for preventing excessive inflammatory responses. They also compete with pathogens for adhesion sites and nutrients, train innate immune pattern recognition, and modulate the production of secretory IgA, the antibody that lines mucosal surfaces. Hidalgo-Cantabrana 2017
Probiotic supplementation has been studied extensively in this context. The evidence is most robust in specific clinical scenarios — antibiotic-associated diarrhoea, certain gastrointestinal infections, and allergic conditions — and more equivocal for general immune modulation in healthy adults. A systematic review of randomised controlled trials found that probiotic supplementation had limited effects on circulating immune and inflammatory markers in healthy adults without disease, though effects in clinical populations were more pronounced. Mohr 2020
In allergic rhinitis — an immune dysregulation condition — a randomised controlled trial found that a specific probiotic mixture produced measurable improvements in symptoms and faecal microbiota composition, suggesting that targeted probiotic intervention can modulate immune responses in atopic conditions. Lungaro 2024
The relationship between gut microbiota and systemic immunity extends to oncology. Research examining probiotic Clostridium butyricum therapy in lung cancer patients found associations with improved survival and response to immune checkpoint blockade — a finding that, while preliminary, illustrates the mechanistic depth of the gut-immune relationship. Tomita 2021
Tributyrin — a prodrug of butyrate — is a relevant compound here. As a triglyceride ester of butyric acid, it delivers butyrate to the colon more efficiently than butyrate salts, where it can support colonocyte health and the regulatory T cell differentiation that underpins mucosal immune tolerance. The evidence base for tributyrin specifically is earlier-stage than for probiotics, but the mechanistic rationale is well-grounded in the SCFA-immune literature.
Polyphenols, Antioxidants, and the Inflammatory Dimension of Immune Defence
Immune defence is not only about mounting a response to pathogens — it is equally about resolving inflammation appropriately once a threat has been neutralised. Chronic low-grade inflammation is now recognised as a driver of immune dysregulation, and the polyphenol-rich compounds in KōJō Daily Formula are relevant to this dimension.
Aged Garlic Extract has been studied for its effects on immune cell activity. Organosulphur compounds derived from garlic — including S-allylcysteine — have demonstrated effects on natural killer cell activity and cytokine production in human studies, though the evidence base is more limited than for the core micronutrients discussed above.
Olive Leaf Extract, containing oleuropein, has antioxidant and anti-inflammatory properties that are mechanistically plausible for immune support, though human clinical trial evidence specifically for immune outcomes remains limited. The evidence is sufficient to note the mechanistic rationale without overstating the clinical certainty.
Grape Seed Extract and Pine Bark Extract (standardised for oligomeric proanthocyanidins) are potent antioxidants that reduce oxidative stress in immune cells. Their relevance to immune defence lies partly in protecting immune cell membranes and DNA from oxidative damage — a mechanism shared with vitamin C and selenium.
N-Acetyl Cysteine (NAC) at 600mg is the precursor to glutathione, the cell's primary intracellular antioxidant. Glutathione is essential for lymphocyte proliferation and function; NAC supplementation has been shown to restore glutathione levels in conditions of oxidative depletion. The immune relevance is mechanistically well-supported, though the clinical evidence in healthy populations is less definitive than in disease states.
Vitamin A at 750mcg RAE deserves specific mention. EFSA's NHC register approves the wording "Vitamin A contributes to the normal function of the immune system," and the mechanistic basis is solid: vitamin A is required for the differentiation of T helper cells, the maintenance of mucosal epithelial integrity, and the production of secretory IgA. Deficiency is associated with significantly increased susceptibility to respiratory and gastrointestinal infections.
The broader point here is that immune defence operates in an oxidative environment, and the capacity to manage that environment — through a network of antioxidant mechanisms rather than any single compound — is integral to immune competence.
What KōJō Daily Formula Does for Immune Defence
KōJō Daily Formula v4.1 addresses immune defence across multiple layers of the system's architecture. Below is a precise account of the relevant ingredients, their exact doses, and the evidence basis for their inclusion.
Core immune micronutrients — EFSA-approved claims:
- Vitamin D3 — 50mcg: Contributes to the normal function of the immune system. Regulates gene transcription in T cells, B cells, macrophages, and dendritic cells. Evidence is particularly strong in deficient populations, which includes a significant proportion of UK adults. Bikle 2022
- Vitamin C — 500mg: Contributes to the normal function of the immune system. Supports neutrophil function, epithelial barrier integrity via collagen synthesis, and lymphocyte proliferation. Carr 2018
- Zinc Bisglycinate — 53mg (16mg elemental): Contributes to the normal function of the immune system. Regulates intracellular signalling in innate and adaptive immune cells, supports T cell maturation, and has direct antiviral properties. Bisglycinate form selected for superior bioavailability. Wessels 2018
- Selenium — 100mcg: Contributes to the normal function of the immune system. Supports selenoprotein synthesis, protects immune cells from oxidative damage, and regulates lymphocyte function. Particularly relevant in the UK context of low dietary selenium intake. Avery 2019
- Vitamin A — 750mcg RAE: Contributes to the normal function of the immune system. Required for mucosal epithelial integrity, T helper cell differentiation, and secretory IgA production.
Gut-immune interface:
- Bacillus coagulans GBI-30, 6086 — 2 billion CFU: A spore-forming probiotic with stability advantages over conventional lactobacillus strains. Supports gut microbiota composition and the gut-immune interface. Evidence for probiotics in immune modulation is strongest in clinical populations and specific conditions. Wilkins 2017
- Tributyrin — 500mg: A butyrate prodrug that delivers butyrate to the colon, where it supports colonocyte health and regulatory T cell differentiation. Mechanistic rationale is well-grounded in the SCFA-immune literature.
Antioxidant and anti-inflammatory support:
- N-Acetyl Cysteine — 600mg: Precursor to glutathione, the primary intracellular antioxidant. Supports lymphocyte function under conditions of oxidative stress.
- Aged Garlic Extract — 600mg: Organosulphur compounds with evidence for effects on natural killer cell activity and cytokine modulation.
- Olive Leaf Extract — 500mg: Contains oleuropein; antioxidant and anti-inflammatory properties mechanistically relevant to immune cell protection.
- Grape Seed Extract — 200mg: Oligomeric proanthocyanidins with antioxidant properties that protect immune cell membranes from oxidative damage.
- Pine Bark Extract — 150mg: Further oligomeric proanthocyanidin source; contributes to the antioxidant network supporting immune cell integrity.
- Alpha Lipoic Acid — 200mg: Both water- and fat-soluble antioxidant that regenerates other antioxidants including vitamin C and glutathione, supporting the broader redox network relevant to immune cell function.
- Vitamin E — 15mg: Fat-soluble antioxidant that protects immune cell membranes. EFSA's NHC register approves the wording "Vitamin E contributes to the protection of cells from oxidative stress."
Additional micronutrients with immune relevance:
- Folate — 400mcg: Required for the rapid cell division that characterises immune responses. EFSA approves the claim that folate contributes to normal immune function.
- Vitamin B6 — 2.8mg: Involved in the synthesis of immune signalling molecules. EFSA approves the claim that vitamin B6 contributes to normal immune function.
- Copper — 2mg: Required for the function of immune cells including neutrophils and macrophages. EFSA approves the claim that copper contributes to normal immune function.
- Iron is not present in KōJō Daily Formula — a deliberate formulation decision, as iron supplementation in replete individuals carries oxidative risk and can promote pathogen growth.
The immune system is complex enough that no supplement replaces the foundational determinants of immune competence: adequate sleep, a varied diet, regular physical activity, and not smoking. What the evidence supports — and what KōJō Daily Formula is designed to address — is the nutritional dimension of that foundation: ensuring that the micronutrients with the strongest mechanistic and clinical evidence for immune function are present at meaningful doses, in bioavailable forms, consistently. That is a more modest claim than most supplement marketing makes. It is also, I think, a more honest one.
Frequently Asked Questions
I eat reasonably well and don't have obvious deficiencies. Will supplementing vitamin D, zinc, and vitamin C actually make a difference to my immune function?
The evidence is strongest if you're deficient, which many UK adults are for vitamin D. For zinc and vitamin C, if you're already adequately nourished, additional supplementation shows modest benefit mainly under physical stress. The real value is correcting any gap in your current status.
Why does the article distinguish between deficient populations and well-nourished people? Doesn't a nutrient either support immune function or it doesn't?
Because restoring a deficiency restores function; supplementing beyond adequacy doesn't necessarily add further benefit. A meta-analysis in selenium-deficient elderly patients tells you something quite different from a trial in well-nourished athletes. The distinction determines whether an intervention is clinically relevant to you.
You mention vitamin D is a steroid hormone, not a vitamin. Does that mean it works differently than the other nutrients in KōJō?
Yes. Vitamin D binds to nuclear receptors on immune cells and directly regulates gene transcription. Vitamin C and zinc work through different mechanisms—antioxidant protection and enzyme cofactor roles respectively. All three are evidence-supported, but they act at different layers of immune architecture.
The article says vitamin C supplementation doesn't prevent colds in the general population. So why is it in the formula?
Because vitamin C supports epithelial barrier integrity, neutrophil function, and lymphocyte proliferation mechanistically. Clinical benefit appears strongest in deficient individuals or those under significant physical stress. It's part of a multi-layered approach, not a standalone cold preventative.
You mention zinc bisglycinate has superior bioavailability. Does that mean the dose in KōJō is lower than it would need to be with other zinc forms?
Bioavailability matters because absorption determines what actually reaches your immune cells. Zinc bisglycinate requires a lower absolute dose to achieve the same functional benefit as poorly absorbed forms like zinc oxide. The formula is dosed based on what's actually absorbed, not just raw milligrams.
