There’s No Substitute for Sunlight: The Essential Influence of Nature’s Sunshine Vitamin on Health | DonnieYance.com
The distribution of community outbreaks of the current global pandemic shows
seasonal patterns associated with latitude, temperature, and humidity, which is
similar to the behavior of seasonal viral respiratory tract infections.
The seasonality of many viral infections is associated with a lack of sunlight, which results in low 25(OH)D concentrations and an uptick in diseases such as respiratory syncytial virus (RSV) infection.,, While it’s obvious that winter in temperate climates interferes with sufficient exposure to ultra violet rays, the rainy season in tropical climates also results in low UVB exposure.
Low levels of vitamin D can cause immune dysfunction, including lack of antibody production and increased risk of inflammation. With regard to respiratory function, low levels of vitamin D are associated with numerous pulmonary diseases, including acute lung injury and acute respiratory distress syndrome. Vitamin D and its receptors have been shown to protect epithelial barriers in various tissues, and offer protection against acute respiratory distress syndrome (ARDS) and fibrosis.  Vitamin D also appears to calm inflammation. In one study, providing vitamin D-deficient mice with vitamin D3 suppressed signs of lung inflammation.
Vitamin D can lower the risk of infections by inducing cathelicidins and defensins that reduce viral replication rates and diminish concentrations of pro-inflammatory cytokines. These inflammatory compounds injure the lining of the lungs and increase the risk of pneumonia. Vitamin D enhances protection by increasing concentrations of anti-inflammatory cytokines.
As an immune system modulator, vitamin D strongly influences immune function and is well known for its ability to enhance immune response when at optimal serum and tissue levels.