What is the purpose of each ingredient in Histamine Block?

Ingredient	Purpose
Vitamin C	Plays a crucial role in DAO production and a healthy inflammatory response.†
DAO (diamine oxidase)	The enzyme that breaks down histamine in various parts of the body - especially the small intestine, colon, placenta, kidney, appendix, testis and prostate.†

Sources:

https://www.genecards.org/cgi-bin/carddisp.pl?gene=AOC1#expression

https://atlasgeneticsoncology.org/gene/53470/ 

†These statements have not been evaluated by the Food and Drug Administration (FDA). This product is not intended to diagnose, treat, cure, or prevent any disease.