Vitamin D3
It has been shown that low vitamin D levels have immunologic implications with a significant decrease in immune function, affecting respiratory health.  This is most likely because the vitamin D receptor is expressed by several immune cells including monocytes, macrophages, dendritic cells, B and T cells. Supplementation with vitamin D has been shown to  modulate NK cell activity to promote a healthy innate immune response. Along with these immune-supporting benefits, vitamin D has also been shown to support the respiratory system and epithelial tight junction integrity.

Vitamin C

Vitamin C is a potent antioxidant that has been studied for many years for its immune-supporting effects. Through its antioxidant functions, vitamin C has been shown to protect important immune cells from oxidative damage.  Data shows vitamin C is heavily concentrated in macrophages, supports lymphocyte activity, modulates cytokine release, improves endothelial function, restores mitochondrial function, and can directly support a challenged immune system.  Of particular interest, vitamin C has been shown to recycle oxidized quercetin back to its parent compound, which supports a robust immune response while increasing the efficacy of quercetin.

Quercetin is best known for its antioxidant activity in scavenging free radicals. Additionally, quercetin helps balance cytokine levels and improve T-lymphocyte balance.  May help zinc enter the cells to combat viral pathogens.* 

N-Acetyl-L-Cysteine

N-Acetyl-L-Cysteine (NAC) is the precursor of the master antioxidant, glutathione. NAC has been shown to support mucus clearance and normal respiratory function, through its ability to cleave disulfide bonds in mucus.