The role of vitamin D in the immune system

Does Vitamin D improve the immune system?

A large body of scientific evidence shows that vitamin D affects the immune system and helps support systemic health. Vitamin D acts as an immune booster and vitamin D deficiency is associated with immune disorders and an increased risk of infection.  Vitamin D is not just a nutrient; It is a hormone that has receptors in almost every cell and tissue of the body. Research has linked vitamin D levels to more than 53 different disease conditions including Alzheimer’s disease, cancer, MS, osteoporosis, diabetes, depression and COVID-19. It is estimated that about 3% of the human genome is regulated by the endocrine system with vitamin D and that more than 1,000 genes in the human body are affected. 

Many diseases including influenza appear seasonal winter. Some researchers hypothesize that this seasonality is caused by reduced exposure to sunlight during the winter months. In northern climates, between November and March, vitamin D cannot be produced from exposure to sunlight. During these months, the angle of the sun prevents the majority of UV light from passing through the atmosphere and thus from reaching our skin to stimulate vitamin D production. As a result, vitamin D levels drop significantly during the winter. 

How does vitamin D boost the immune system?

Vitamin D is involved in immunity through several mechanisms and plays a role in regulating both the innate and adaptive immune response in the body. Vitamin D affects immune health by interacting with vitamin D receptors on innate immune cells throughout the body. Innate immunity is the body’s nonspecific first line of defense against foreign pathogens. 

Vitamin D builds immunity and helps fight infection by regulating the activity of immune cells that provoke antiviral responses. Vitamin D binds to receptors found in immune cells such as neutrophils, macrophages, and natural killer cells. Vitamin D stimulates these cells to produce peptides with antiviral properties that defend the body against foreign pathogens. Cathelicidins and defensins are peptides that have immunomodulating and antimicrobial capabilities and act as antiviral agents as part of the innate immune system. Multiple studies have shown that vitamin D metabolites play a role in enhancing the production of the human form of cathelicidins and defensin, thereby enhancing the innate immune response. Studies have shown that vitamin D plays a role in activating these cells to help the body fight infections.

Vitamin D acts as an immune system modifier by suppressing inflammation associated with both the innate and adaptive immune response. In response to foreign pathogens, the immune system releases small proteins called cytokines, which trigger an immune response to help fight the virus. Sometimes this response to infection goes into overdrive and excessive amounts of cytokines are released. This is known as a cytokine storm and can cause excessive inflammation. This inflammation can damage organs throughout the body, resulting in effusions, lung injury, acute respiratory distress syndrome, disseminated intravascular coagulation, kidney failure, and ultimately death.

Immune system benefits of vitamin D

Several studies have looked at the role of vitamin D in immunity against respiratory infections. A systematic review of 25 randomized controlled trials concluded that vitamin D supplementation significantly reduces the risk of acute respiratory infection. Another study looking at the effect of vitamin D on respiratory function found that each 10 nM/L increase in the blood level of vitamin D reduced the risk of respiratory tract infection by 7%.

Research has also found that vitamin D builds immunity against the flu and colds. Vitamin D deficiency is more prevalent in the winter when cold and flu season peaks. Clinical trials have shown that increasing the level of vitamin D has been shown to reduce the incidence of influenza. 

Research shows that low levels of vitamin D increase the risk of autoimmune diseases, including multiple sclerosis, rheumatoid arthritis, diabetes, and inflammatory bowel disease. Individuals with these conditions often have low levels of vitamin D and studies have indicated that vitamin D deficiency may contribute to both the development and severity of these conditions. 

Early correlative research strongly suggests a link between vitamin D level and the risk and severity of coronavirus outcomes. In one study, researchers found that patients over 40 were 51.5% less likely to die from COVID-19 if they had an adequate level of vitamin D, which they defined as at least 30 ng/ml. Another study of 185 patients diagnosed with COVID-19 found that patients with vitamin D deficiency had a higher rate of hospitalization and required more intensive oxygen therapy and invasive mechanical ventilation. In these patients, vitamin D deficiency was associated with a 6-fold higher risk of severe disease and a 15-fold higher risk of death. 

Vitamin D and the immune system

More research is needed to determine the exact dose of vitamin D required to enhance the function of the immune system. 

The Institute of Medicine (IOM) recommends that the dietary allowance of vitamin D be 600 international units (IU) per day. This recommendation is based on what is needed to prevent rickets and osteoporosis, not what is needed to support the immune system. Many vitamin D researchers disagree with this recommendation and say the IOM recommended allowance is not enough to prevent deficiency or support bone health. In general, 4,000 IU or less per day is considered safe, as long as your blood values ​​are monitored. It is important to avoid excessive doses of oral vitamin D. If the intake of vitamin D is too high, it can cause high levels of calcium in the blood and potentially dangerous consequences.

Getting vitamin D from light allows your body to self-regulate vitamin D production and achieve what it needs to stay healthy, without the risk of overdose or toxicity. Unlike oral supplements, you cannot overdose on the vitamin D3 that your skin produces. If you have enough vitamin D, your body will produce less.