Blackmores Institute

The review reports that vitamin D, through several mechanisms, can reduce risk infections and reduce concentrations of pro-inflammatory cytokines responsible for the inflammation that injures the lining of the lungs, leading to pneumonia by inducing cathelicidins and defensins.
 
 Cathelicidins exhibit direct antimicrobial activities against a spectrum of microbes, including Gram-positive and Gram-negative bacteria, enveloped and nonenveloped viruses, and fungi. Vitamin D also enhances cellular immunity, in part by reducing the cytokine storm induced by the innate immune system. Administering vitamin D reduces the expression of pro-inflammatory cytokines and increases the expression of anti-inflammatory cytokines. Vitamin D is also a modulator of adaptive immunity as 1,25(OH)2D3 suppresses responses mediated by the T helper cell type 1 (Th1).
 
 Claiming that seasonal influenza generally peaks in winter which coincides with decreases in solar UVB doses and thus 25(OH)D concentrations, the authors suggest that raising levels of vitamin D could reduce the risk of influenza.
 
 “Mean serum 25(OH)D concentrations in north and central regions of the United States are near 21 ng/mL in winter and 28 ng/mL in summer, whereas in the south region, they are near 24 ng/mL in winter and 28 ng/mL in summer. In addition, the winter peak of influenza also coincides with weather conditions of low temperature and relative humidity that allow the influenza virus to survive longer outside the body than under warmer conditions. Ecological studies suggest that raising 25(OH)D concentrations through vitamin D supplementation in winter would reduce the risk of developing influenza,” the authors explained.
 
 “Seasonal influenza has a high health burden. According to one recent estimate 389,000 (uncertainty range 294,000–518,000) respiratory deaths were associated with influenza during the period 2002–2011,” the authors said.
 
 According to the authors serum 25(OH)D concentrations decrease with age, attributing this decline to less time spent in the sun reducing production of vitamin D as a result of lower levels of 7-dehydrocholesterol in the skin, additionally some pharmaceutical drugs reduce serum 25(OH)D concentrations by activating the pregnane-X receptor.
 
 “Vitamin D supplementation is required for many individuals to reach 25(OH)D concentrations above 30 ng/mL, especially in winter. However, vitamin D fortification of basic foods such as dairy and flour products can raise serum 25(OH)D concentrations of those members of various populations with the lowest concentrations by a few ng/mL. Doing so can result in reduced risk of acquired respiratory tract infections for individuals with extreme vitamin D deficiency. However, for greater benefits, daily or weekly vitamin D supplementation is recommended, as is the annual determination of serum 25(OH)D concentration for those with health risks.
 
 “Vitamin D3 supplementation should be started or increased several months before winter to raise 25(OH)D concentrations. The goal should be to raise 25(OH)D concentrations above 40-60ng/mL (100-150nmol/L).”
 
 It also prudent that magnesium supplementation be recommended when taking vitamin D supplements. Magnesium helps activate vitamin D, and all the enzymes that metabolize vitamin D seem to require magnesium as a cofactor.
 
 “The hypothesis that vitamin D supplementation can reduce the risk of influenza incidence and death should be investigated in trials to determine the appropriate doses, serum 25(OH)D concentrations, and the presence of any safety issues,” the authors said.
 
 “Available evidence indicates that supplementation with multiple micronutrients with immune-supporting roles may modulate immune function and reduce the risk of infection. Micronutrients with the strongest evidence for immune support are vitamins C and D and zinc. Better design of human clinical studies addressing dosage and combinations of micronutrients in different populations are required to substantiate the benefits of micronutrient supplementation against infection,” the review concluded.
 
 
 Source:
 Nutrients. 2020. DOI:<a href="https://www.mdpi.com/2072-6643/12/4/988">10.3390/nu12040988</a>

Researchers are calling for large randomised controlled trials after a new review finds evidence that vitamin D may reduce the risk of influenza.

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