John KIRAGU
- May 12
- 5 min read

The link between vitamin D and immune function: How cod liver oil can help

"Vitamin D can regulate adaptive and innate immune responses by increasing the production of antimicrobial peptides and killing bacteria" - John K.

Photo by Sebastian Coman on Pexels

Vitamin D modulates the adaptive immune system by having a direct effect on the functioning of antigen-presenting cells (APCs), T cell activation, and phenotype. It blocks B-cell differentiation and immunoglobulin secretion, thus inhibiting B-cell proliferation. Vitamin D's modulation of the immune system has a pleiotropic action on various chronic diseases, including cardiovascular diseases, cancer, autoimmune diseases, neurologic diseases, and diabetes.

Vitamin D deficiency leads to increased susceptibility to various autoimmune diseases such as inflammatory bowel disease, multiple sclerosis, insulin-dependent diabetes mellitus, rheumatoid arthritis, and systemic lupus erythematosus. You can obtain the daily recommended intake of vitamin D from food or supplements such as cod liver oil, salmon, herring, sardines, canned tuna, egg yolks, mushrooms, and vitamin D-fortified foods.

Role of Vitamin D in Immune Function

Vitamin D is considered unique as it is one of the two vitamins that can be produced by your body (the other is vitamin K) and can also be obtained from other sources such as food or supplements. Vitamin D is technically a hormone that moderates the amount of calcium in your blood and helps in the absorption of other minerals such as phosphorous, which are essential for the growth and maintenance of your bones.

While we often associate vitamin D with musculoskeletal health, it also has various functions in the body, such as the role it plays in reducing inflammation and immune functions. Low serum levels of calcidiol, a form of vitamin D, are linked with greater susceptibility to infections such as viral infections, influenza, and tuberculosis. Vitamin D activates the T-cells (killer cells), which detect and destroy foreign pathogens such as bacteria and viruses.

This makes vitamin D a vital nutrient for maintaining a functioning immune system that can fight off pathogens. Vitamin D also plays a vital role in bone metabolism and calcium homeostasis. Severe vitamin D deficiency or chronic deficiency leads to a decline in intestinal phosphorus and calcium absorption, which causes hypocalcemia that, leads to secondary hyperparathyroidism, which later causes accelerated bone demineralization and phosphaturia. The symptom associated with these conditions includes:

Bone pain
Osteoporosis
Myalgias (muscle pain)
Arthralgias (joint stiffness)
Fatigue

Vitamin D influences immune health by interacting with vitamin D receptors on the innate immune cells, which are the first line of defense against pathogens in the body. Vitamin D stimulates the defensins and cathelicidins peptides that have an immune modulating capability and are antimicrobial.

Surprisingly, vitamin D acts as an immune system regulator by suppressing inflammation linked with adaptive and innate immune responses. Excess amounts of cytokines that are released when your immune response fights pathogens can lead to hyper inflammation that can damage body organs, leading to acute respiratory distress syndrome, lung injury, pulmonary infiltrates, and renal failure.

Studies have linked vitamin D with immunity against respiratory infections. The intake of vitamin D supplements, such as cod liver oil, significantly reduces the risk of acute respiratory tract infections. Vitamin D also helps to build immunity against colds and flu, and an increased level of vitamin D is associated with a decreased incidence of influenza.

Cod liver oil

Cod liver oil is a type of supplement obtained from fish oil that has various health benefits. It is rich in vitamin A and D, healthy fats, antioxidants, and high in omega -3 fatty acids which has various health benefits such as lower cholesterol and inflammation.

Here are some scientifically supported benefits of cod liver oil and its impact on your immune response.

Reduces inflammation

Inflammation is natural occurring process when your immune system fights foreign pathogens and heal injuries. Cod liver oil contains sufficient amounts of vitamin A, D, and omega 3-fatty acids that help to prevent the risk chronic inflammation. Both vitamin A and D contained in cod liver oil are antioxidants which reduces inflammation by binding and neutralizing harmful free radicals that may cause inflammation.

Improves bone health

It is better to maintain healthy bones as you age because when you are aging, you start to lose your bone mass which can result in fractures. Cod liver oil is a powerful source of vitamin D which helps to reduce age-related bone loss because it enhances the absorption of calcium which is an essential mineral for strong bones, from the gut.

Photo by Michele Blackwell on Unsplash

The intake of vitamin D supplement such as cod liver oil accompanied by diets rich in calcium help to reduce bone loss in adults. Taking vitamin D supplements such as cod liver oil is essential for people who live far from equator since there skin does not get sufficient sunlight to synthesize vitamin D.

Promotes joint health

Cod liver oil may improve the symptoms of rheumatoid arthritis an autoimmune disease that is characterized by joint damage, kidney problems, and heart issues while reducing joint pains. Although there is no current cure for rheumatoid arthritis, the intake of cod liver oil can reduce the pain from rheumatoid arthritis enough to help the patient to reduce the reliance on corticosteroids and nonsteroidal anti-inflammation drugs. Rheumatoid arthritis such as swelling and stiffness can be reduced by the intake of cod liver due to presence of omega-3 fatty acids which as a vital role in reducing joint inflammation and protecting them against damage.

Lowers the risks of cancer

The cod liver oil has an incredible amount of vitamin D which has been linked to lower risks of cancer. Vitamin D from cod liver oil and sun can help to prevent breast cancer due to its proapototic and antiproliferative effects on the breast cells hence reducing breast tumor. The lack of enough vitamin D has been linked with risks of various types of cancer such as breast, colon, ovarian, and multiple myelomas.

Vitamin D not only plays a role in the maintenance of healthy and strong bones but also engage in the process of repairing defective genes formed by the process known as mis-match repair (MMR) which requires active vitamin D to function properly.

Vitamin D is a vital nutrient that helps the immune system to stay balance by binding the receptors on immune cells like macrophages, neutrophiles, and natural killer cells. It also stimulates these cells to produce peptides which provides first line defense against bacterial and viral infections while restricting adaptive immune response which may enhance the inflammatory response that may further lead to acute respiratory distress.

Cod liver oil also has a great impact in the body as it contains a combination of vitamin A, omega-3 fatty acids, and vitamin D which are essential for reduced inflammation, strong bones, and less joint pain for those with rheumatoid arthritis. The common doses for cod liver oil supplementation are 1-2 teaspoons per day or try the capsule form.