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Quercetin and green tea for flu prevention

The flu vaccine fiasco in the U.S., combined with the threat of a disastrous bird flu epidemic in the near future, has created an incentive to look for alternative influenza preventatives. (At least, such an incentive exists in the U.S., which is apparently the only country in the industrialized world with a medical system sufficiently inept for this fiasco to happen.) Two of the most promising of these alternative flu preventatives are quercetin (a substance found in many plants) and EGCG (a substance plentiful in green tea).

Both quercetin and EGCG are examples of polyphenols — a class of biochemicals that are receiving lots of attention from researchers. Although they are antioxidants, some of their important effects in the body are probably due to factors other than their antioxidant activities.

It has been known since the early 1990s that tea polyphenols decrease the ability of influenza viruses to infect human cells. According to recent newspaper reports, producers of green tea products are now gearing up production in anticipation of increased demand during this flu season.

Quercetin’s antiviral effects were discovered in the early 1980s. Despite the fact that many studies have been performed since then to elucidate the mechanisms for this and other quercetin activities, these mechanisms are still not understood. Nevertheless, quercetin is known to reduce the infectivity of various viruses, including flu viruses.

Link to news article about green tea and flu:

Link to abstract of research article about green tea and flu:

Link to abstract of research article about quercetin and flu:


The absorption of quercetin by the digestive tract is normally fairly high — about 36–53%, according to one study. Experimentation by AIDS patients suggests that it can be increased further by heating quercetin in coconut milk and drinking the mixture.

Link to abstract of article about quercetin absorption:

Link to article about quercetin in coconut milk:


You will often hear people claim that nutritional substances, such as quercetin, should be obtained from the diet rather than from supplements. This is only true for a few such substances — mainly, those that work synergistically with other components of the food they occur in. It certainly is not true for quercetin. Onions, for example, are sometimes touted as a good source of quercetin. But the arithmetic tells a different story: onions vary widely in how much quercetin they contain, and even for the best of them you would have to eat about a kilogram (two pounds) of onions per day in order to get the amount of quercetin in one supplement capsule.

Link to news story touting onions as a source of quercetin:

Link to chart showing quercetin content of onions:


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