Physical Health and Wellbeing

How Vitamin D3 Boosts Immune Function and Fights Infections

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While vitamin C is often mentioned as a super nutrient that supports immune health, two additional super nutrients are non-negotiable for immune function: zinc and vitamin D.

Vitamin D, which we commonly think of as a nutrient that promotes bone health, has many other benefits and roles in the body. Let’s learn how vitamin D3 boosts immune system function and fights infections.

How Vitamin D3 Boosts Immune Function and Fights Infections

Boosts Killer Cells

While vitamin D2 and D3 similarly float into our receptor sites, D3 seems more potent. A glut of recent research, including a study published in Frontiers in Immunology, indicates that only vitamin D3 helps enable a critical immune response to bacterial and viral threats.

Vitamin D supports the respiratory tract’s innate immune response by binding to cells that express antiviral peptides like cathelicidins and defensins. These peptides have been found to bind to viral envelope glycoproteins and inhibit virus entry.

Researchers gave 335 participants either a placebo or 15 micrograms of D3 during a grey English winter. On day 7, those who took D3 displayed significantly higher NK and NKT cell counts and a lower NLR than the control group. They also had reduced levels of CRP and procalcitonin. This indicates that D3 can help bolster the body’s resistance to coronavirus infection and related complications, including pulmonary edema and acute respiratory distress syndrome (ARDS).

Read more: My Experience Having Covid-19

Fights Inflammation

A swollen ankle after you scrape it is healthy – it’s your immune system marshalling forces against invading germs. But too much inflammation can lead to heart disease, cancer, diabetes, and autoimmune diseases like rheumatoid arthritis and psoriasis.

Vitamin D impacts the body’s innate immune system, its non-specific first line of defence against bacteria and viruses. Vitamin D receptors are expressed by innate immune system cells and regulate key inflammatory responses.

A woman standing in a field of sunflowers, smiling.
Photo by Courtney Cook on Unsplash

Prevents Infections

Vitamin D is important for bone health and plays a crucial role in regulating the body’s immune response to microbial threats. Immune cells such as macrophages and monocytes contain the enzyme CYP27B1, which converts inactive 25-hydroxyvitamin D to active 1,25-dihydroxyvitamin D (2,25(OH)D), as well as the vitamin D receptor (VDR).

Activation of these pathogen recognition receptors triggers the production of antimicrobial peptides and the upregulation of genes that promote front-line innate immune responses. This response can help prevent infection by limiting the spread of the virus or at least lessen its severity.

Read more: How to Quickly Fight Off a Cold

Reduces Risk of Cancer

Extensive molecular evidence shows that vitamin D signalling promotes antibacterial and antiviral innate immune responses. This has been confirmed by clinical studies showing that vitamin D enhances the cellular response to pathogens and reduces the severity of infection.

Vitamin D is a hormone the body makes in the skin from sunlight. Taking nutrient supplements can help prevent Rickets in infants and Osteomalacia in adults, which are skeletal deformities caused by insufficient calcium absorption from food.

The ‘sunshine vitamin’ is also thought to reduce the risk of cancer by reducing inflammation and stimulating the growth of healthy cells that can fight off tumours. Epidemiologic (studies of populations of people) and laboratory experiments show that Vitamin D inhibits cancer development in multiple ways, including preventing cell division, decreasing tumour blood vessel formation, and stimulating cell death. Vitamin D3 is being studied in some clinical trials for its effect on the risk and progression of colorectal cancer.

Read more: 10 Natural Ways to Boost Your Immune System at Home

A woman with her eyes closed and the sun shining on her face.
Photo by Fleur Kaan on Unsplash


  1. I have sometimes suffered with low vitamin d and had to be prescribed some from my doctor that are high strength. I have been looking for some good ones to take regularly. This was so informative. Thank you for sharing.
    Lauren – bournemouthgirl

    1. Sophie says:

      Thank you for sharing your experience – I’m glad you found this informative!

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