Vitamin D’s immune-regulating and anti-viral functions

Many of us contract respiratory infections during the winter period. In many cases, the underlying cause is a deficiency of vitamin D, a key nutrient for immune health. Vitamin D also regulates the body’s inflammatory response, thereby preventing it from getting out of hand and becoming complicated or life-threatening. In a new review article, researchers looked at vitamin D’s role in preventing and fighting acute respiratory infections such as COVID-19 and influenza with particular focus on children and youngsters. The scientists point out that many people need to take higher doses of vitamin D to optimize levels of the nutrient in their blood.

Acute respiratory infections are one of the main reasons why people go to see their physician, especially families with children. Over the past years, there has been a lot of focus on vitamin D’s role in protecting the upper respiratory tract, especially against infections caused by rhinovirus (the common cold), influenza virus, COVID-19, and other lower respiratory tract infections such as bronchitis and pneumonia, which can even be caused by other microorganisms.
There has not been all that much focus on having optimal blood levels of vitamin D, however. The new review article therefore aimed at looking closer at this in relation to various respiratory infections that can develop in entirely different ways.
Most people have few and moderate symptoms or none at all. In some cases, the immune defense can be weak or become unhinged, so related infections occur. In very rare situations, infections with COVID-19 or influenza can cause cytokine storm and hyperinflammation and cause severe damage to vital organs and the cardiovascular system. There is not a lot of clinical data on COVID-19 and other infections with regard to children and youngsters. The authors carefully scrutinized 27 studies of how being vitamin D-deficient or taking supplements of vitamin D affects the risk of becoming infected and the severity of respiratory infections.

• Many children and youngsters are vitamin D-deficient
• This is particularly true for immigrant children during the winter period
• Severe vitamin D deficiency is most prevalent among infants, small children, and children in puberty
• Vitamin D deficiency is also widespread among adults

Vitamin D deficiency increases the risk of respiratory infections and complications

Respiratory infections and lack of vitamin D are significant global health problems among children and youngsters. Studies show that lack of vitamin D increases the risk of colds, bronchitis, influenza, and pneumonia that typically occur during the winter period and is a huge human and socio-economic burden. Being vitamin D-deficient also seems to increase the risk of other respiratory infections like COVID-19, and it also increases the risk of these infections becoming so complicated that patients require hospitalization. Blood levels of vitamin D appear to be inversely related to levels of inflammation markers and the severity of COVID-19 and other respiratory ailments.

Vitamin D supplementation aimed at optimizing blood levels of the nutrient

Generally speaking, vitamin D supplementation can lower the risk of a respiratory infection. In a meta-analysis of 4,786 children, vitamin D supplementation administered in combination with antibiotics was seen to effectively help treat pneumonia. Vitamin D supplements given to babies and children who have had pneumonia also prevent recurrence. What is important here is to make sure to optimize blood levels of vitamin D. In the current review article, there is a consensus that blood levels of vitamin D should be at least 75 nmol/L. The scientists recommend for all age groups to avoid becoming deficient. They also say that whenever it is needed, people should take a vitamin D supplement to have optimal levels in the blood.

How does vitamin D affect our immune defense?

The type of vitamin D that we humans synthesize in our skin or get from (most) supplements is inactive and must be converted into the active steroid form called 1,25-dihydroxyvitamin D. This process starts in the liver and is continued in the kidneys, in the white blood cells, and in other tissues.
Most cells in our body have receptors for the active form of vitamin D, which is able to enter the cells and control genes by means of different on-off switches. The same goes for various white blood cells such as dendritic cells, macrophages, T cells, and B cells. Vitamin D is also important for certain antibiotic peptides in the respiratory tract and for repairing protective epithelial cells in the respiratory tract, the circulatory system, and other tissues.
That is how vitamin D activates the innate immune defense that is designed to handle most germs and pathogens without causing symptoms, and also controls the adaptive immune defense that is more specialized and produces antibodies.
Vitamin D also controls the inflammatory processes and prevents them from getting out of hand and causing damage. Vitamin D can inhibit pro-inflammatory cytokines (IL-1, IL-6, IL-12, IL-17 and TNF-α) and increase anti-inflammatory cytokines (IL-10) via metabolic processes (NFKβ)
In their review article, the authors write about how vitamin D prevents a COVID-19 infection from developing complications caused by cytokine storm and hyperinflammation in the lungs, the blood vessels, and in other organs. In worst case, these complications can lead to circulatory failure and death. It is not the virus in itself that makes respiratory infections complicated. It is because the immune defense is too weak to fight the infections, or because the immune defense reacts with unhinged inflammation that damages healthy tissue.

Recommendations for vitamin D and safe upper limit (children and adults)

• The Danish Health Authority recommends all-year vitamin D supplementation for children aged 0-4 years
• The same goes for children who don’t get enough sun exposure during the summer period or have dark skin
• It is important to have optimal blood levels of vitamin D all year round throughout life
• EU’s Scientific Committee on Food has established the following daily safe upper intake levels for vitamin D: 25 µg for infants 0 - 6 months, 50 µg for children aged 6 months - 10 years, and 100 µg for children aged 11 years and older plus adults.

References:

Immunomodulatory Effects of Vitamin D in Respiratory Tract Infections and COVID-19 in Children. Nutrients 2023

Priyom Bose. The immunomodulatory and antiviral function of vitamin D. News Medical Life Sciences 2023.

Signe Sparre Beck-Nielsen & Christian Mølgaard. D-vitaminmangel hos børn og unge I Danmark. Ugeskrift for læger. 2015