“Your immune system is your first-line defense against all types of infections, be they bacterial or viral, so the most effective way to prevent infectious illness — including influenza — is a robust immune system. Your diet and other lifestyle factors are foundational for good immune function, but certain supplements can also be quite helpful.
One such supplement is quercetin, an antioxidant flavonol found naturally in apples, plums, red grapes, green tea, elder flower and onions, just to name a few. For a more exhaustive list, see Superfoodly's ranking of the top 100 quercetin-packed foods. Quercetin has been shown to combat inflammation and acts as a natural antihistamine. Elder flower extract, which is rich in quercetin, has been traditionally used as a tonic to boost immunity. It is also widely known to promote lung and bronchial tract health.
Quercetin is also available in supplement form and has been used to ameliorate obesity, Type 2 diabetes, circulatory dysfunction, chronic inflammation, hay fever and mood disorders. A number of studies have also highlighted quercetin's ability to prevent and treat both the common cold and influenza.”
Superfoodly's ranking of the top 100 quercetin-packed foods: