Zinc is a mineral that works synergistically with vitamin A in activating thymic factor. Thymic factor is a thymus hormone with important immune-supporting properties (Dardenne et al 1982).  Maintaining optimal zinc levels also helps maintain helper T-cell lymphocyte function, natural killer cell activity, macrophage function, and antibody production (PDR Health).  In other words, zinc is a bolster to the functioning of your immune system. Some studies have found that zinc lozenges may reduce the duration of a cold, perhaps by as much as 50%, and may reduce the number of upper respiratory infections in children (WebMD 2019) (Orthomolecular). 

Vitamin C is well known for its ability to support the immune response. Vitamin C concentrations decline rapidly in the body during periods of stress. Dietary intake is therefore crucial during immune challenges.  Vitamin C has been found to be helpful in supporting specific components of the immune system including NK cell activity and lymphocyte function.  Vitamin C also provides antioxidant support by protecting cells against reactive oxygen species that are generated during a normal inflammatory response (Wintergerst et al 2006) (Orthomolecular).

Elderberry can help treat cold and flu symptoms and reduce congestion. One study suggested that using a standardized elderberry extract could shorten the duration of flu by about 3 days. Another preliminary study found that a lozenge with elderberry extract helped reduce flu symptoms when taken within 24 hours of symptoms starting. In the lab, a study suggested that elderberry could kill the H1N1 virus ("swine flu") in test tubes, but researchers do not know whether it would be effective against H1N1 in people (PennState Hershey). The bioactive components of elderberry include the flavonoid anthocyanin (Monograph 2005).  Black elderberry preparations have also been shown to enhance immune cell killing potential by supporting healthy cytokine production, including IL-8 and IL-10, the cellular pathways used to eliminate foreign invaders (Barak et al 2002) (Orthomolecular).