Blackmores Institute

For centuries, CLO has been revered in traditional medicine for its broad-spectrum health benefits, from supporting bone and joint health,1 to strengthening immunity.2 With a strong foundation in historical healthcare, CLO was one of the most widely used remedies to prevent and treat rickets in children,3 and was administered to ward off infection, with historical records documenting its use in the early 1800s to treat tuberculosis.2 CLO has also been shown to have a positive impact on immune dysfunction associated with pre-autoimmune conditions.4In naturopathic medicine, CLO exemplifies the principle of the healing power of nature (vis medicatrix naturae), offering a concentrated source of nutrients derived from a wholefood to support the body’s natural defences. Interest in its potential for immune support remains, with emerging research beginning to explore the mechanisms that may help explain its long-standing use.<h3>
 Why CLO continues to be used today</h3>While much of cod liver oil’s reputation is rooted in traditional use, contemporary studies have started to investigate its broader health applications, including the role it may play in supporting immune function and regulating inflammation.A large cohort study reported that infants consuming CLO at least four times per week had a lower risk of allergy-related outcomes by age six.5 In adults, a 2019 randomised, double-blind, placebo-controlled trial demonstrated that CLO supplementation in women with gestational diabetes mellitus improved metabolic markers and reduced systemic inflammation, including high-sensitivity C-reactive protein (hs-CRP).6Recent investigations have also linked CLO intake to cardiovascular benefits, with a recent study reporting more significant reductions in low-density lipoprotein (LDL) cholesterol and total cholesterol levels in patients supplementing with CLO alongside rosuvastatin, rather than rosuvastatin alone.7 Additionally, in older women, regular CLO intake was modestly associated with improved hip bone mineral density.8<h3>
 The nutrients behind CLO’s immune-modulating effects</h3>CLO’s immune benefits are largely attributed to three key bioactive nutrients, vitamin A, vitamin D, and omega-3 fatty acids. Together, these nutrients support both innate and adaptive immunity through enhancing the integrity of mucosal barriers, regulating immune cell activity, and modulating inflammation.4<h3>
 Vitamin A</h3>Essential for both innate and adaptive immunity, vitamin A influences the function of neutrophils, macrophages, natural killer cells, and lymphocytes (see Figure 1).9 It helps maintain epithelial barrier integrity, modulates cytokine production, and supports gut microbiome composition and diversity.9 Deficiency in vitamin A is associated with impaired immune defences, increased susceptibility to infections, and heightened inflammation.9
<img src="https://images.contentstack.io/v3/assets/blt948bd74310fc0ad0/blt91aa68f61ad77331/69f29707c58f74c367257e0b/bi-cod-liver-oil-immune-health-figure1.jpg" alt="bi-cod-liver-oil-immune-health-figure1.jpg" class="embedded-asset" />Figure 1. The immunomodulatory effects of vitamin A.10<h3>
 Vitamin D</h3>Both a vitamin and a pre-hormone, vitamin D modulates the activity of immune cells, including B-cells, T-cells, monocytes, macrophages, dendritic cells, and neutrophils (see Figure 2).11 Low levels of vitamin D are linked with increased susceptibility to infections, autoimmune conditions, and respiratory illnesses.11<img src="https://images.contentstack.io/v3/assets/blt948bd74310fc0ad0/blt792cb741e631513b/69f297092ddd1174749ce0f5/bi-cod-liver-oil-immune-health-figure2.jpg" alt="bi-cod-liver-oil-immune-health-figure2.jpg" class="embedded-asset" />
Figure 2. The immunomodulatory effects of vitamin D.12<h3>
 Omega-3 fatty acids</h3>Omega-3 fatty acids exert potent anti-inflammatory and antioxidant effects, modulating both innate and adaptive immune responses (see Figure 3).13 They also suppress pro-inflammatory cytokines such as tumour necrosis factor and interleukin-6,14 and promote the production of specialised pro-resolving mediators (SPMs), which facilitate the resolution of inflammation without suppressing immune function.15 Omega-3 fatty acids also help maintain a balanced gut microbiome, further enhancing immune health.15<img src="https://images.contentstack.io/v3/assets/blt948bd74310fc0ad0/bltec5a10c263723236/69f297093e47cc3ee2134543/bi-cod-liver-oil-immune-health-figure3.jpg" alt="bi-cod-liver-oil-immune-health-figure3.jpg" class="embedded-asset" />
Figure 3. The immunomodulatory effects of omega-3 fatty acids.13<h3>
 Nutrient synergy: an orchestrated effect</h3>Emerging research suggests that the combination of vitamin A, vitamin D, and omega-3 fatty acids exerts synergistic effects on immune function.One study reported that co-supplementation with this nutrient trio significantly reduced inflammatory markers, even at lower individual doses, compared to higher doses of the nutrients in isolation.4 Additionally, a five-year intervention study found that combined vitamin D and omega-3 supplementation reduced autoimmune disease incidence by 22%.4This nutrient synergy may optimise immune outcomes while mitigating the potential risks associated with high-dose fat-soluble vitamin supplementation.4<h3>
 Conclusion</h3>While further research is warranted to fully understand CLO's immunological potential, both traditional wisdom and contemporary evidence highlight its value as a therapeutic in supporting immune health. By delivering a balanced combination of immune-modulating nutrients, CLO offers a natural, nutrient-dense option for practitioners seeking to support immune function through an integrative, evidence-informed approach. <h3> References </h3><ol><li>Hernigou P, Auregan JC, Dubory A. Vitamin D: part II; cod liver oil, ultraviolet radiation, and eradication of rickets. International Orthopaedics. 2019 Jan 9;43(3):735–49.</li><li>McCullough PJ, Lehrer DS. Vitamin D, cod liver oil, sunshine, and phototherapy: Safe, effective and forgotten tools for treating and curing tuberculosis infections — A comprehensive review. The Journal of Steroid Biochemistry and Molecular Biology. 2018 Mar;177:21–9.</li><li>Lentjes M, Welch A, Mulligan A, Luben R, Wareham N, Khaw KT. Cod Liver Oil Supplement Consumption and Health: Cross‑sectional Results from the EPIC-Norfolk Cohort Study. Nutrients. 2014 Oct 16;6(10):4320–37.</li><li>Bland JS. Therapeutic Use of Omega-3 Fatty Acids for Immune Disorders In Search of the Ideal Omega-3 Supplement. Integrative Medicine: A Clinician’s Journal. 2022 Nov;21(5):14. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC9831136/
 5 Øien, Schjelvaag, Storrø, Johnsen, Simpson. Fish Consumption at One Year of Age Reduces the Risk of Eczema, Asthma and Wheeze at Six Years of Age. Nutrients. 2019 Aug 21;11(9):1969.</li><li>Yang S, Lin R, Si L, Li Z, Jian W, Yu Q, et al. Cod-Liver Oil Improves Metabolic Indices and hs-CRP Levels in Gestational Diabetes Mellitus Patients: A Double-Blind Randomized Controlled Trial. Journal of Diabetes Research. 2019 Dec 28;2019:1–13.</li><li>Fatima F, Memon A, Zafar S, Amar Z, Talpur AS, Hashim S, et al. Role of Cod Liver Oil in Reducing Elevated Lipid Parameters. Cureus. 2021 Jun 9.</li><li>Eysteinsdottir T, Halldorsson TI, Thorsdottir I, Sigurdsson G, Sigurdsson S, Harris T, et al. Cod liver oil consumption at different periods of life and bone mineral density in old age. The British journal of nutrition. 2015 Jul 1;114(2):248–56. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5490077/</li><li>Amimo JO, Michael H, Chepngeno J, Raev SA, Saif LJ, Vlasova AN. Immune Impairment Associated with Vitamin A Deficiency: Insights from Clinical Studies and Animal Model Research. Nutrients. 2022 Nov 26;14(23):5038.</li><li>Biswas S, Biswas S, Gopalakrishnan PadmaPriya, Kaur J, Atreyi Pramanik, Islam F, et al. Role of nutraceuticals in viral infections as immunomodulators: A comprehensive review. eFood. 2024 Aug 26;5(5).</li><li>Mourad Aribi, Franck, Chafia Touil-Boukoffa. Editorial: The role of vitamin D as an immunomodulator. Frontiers in Immunology. 2023 Mar 28;14. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10086413/</li><li>Gholamreza Daryabor, Nasser Gholijani, Fatemeh Rezaei Kahmini. A review of the critical role of vitamin D axis on the immune system. Experimental and Molecular Pathology. 2023 Aug 1;132-133:104866–6.</li><li>Gutiérrez S, Svahn SL, Johansson ME. Effects of Omega-3 Fatty Acids on Immune Cells. International Journal of Molecular Sciences. 2019 Oct 11;20(20):5028. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6834330/</li><li>Mahmut Bodur, Yilmaz B, Duygu Agagunduz, Yeşim Ozogul. Immunomodulatory Effects of Omega‐3 Fatty Acids: Mechanistic Insights and Health Implications. Molecular Nutrition &amp; Food Research. 2025 Mar 30;</li><li>Zou B, Zhao D, Zhou S, Kang JX, Wang B. Insight into the effects of Omega-3 fatty acids on gut microbiota: impact of a balanced tissue Omega-6/Omega-3 ratio. Frontiers in Nutrition. 2025 May 16;12.</li></ol>

<h3>Key highlights:</h3><ul><li>Cod liver oil (CLO) has a rich history in traditional medicine</li><li>It is a natural source of vitamin A, vitamin D, and omega-3 fatty acids - nutrients with well-established roles in supporting immune health</li><li>Evidence suggests a synergistic effect when these nutrients are combined, offering enhanced immune benefits at lower individual doses. </li></ul>Read on to learn about the role of CLO in supporting immune health.

Key highlights:

Recommended for you

Supporting psychological resilience with multivitamins

A holistic approach to supporting detoxification

Blueberries the well known super fruit could help fight Alzheimer's

Understanding the research