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16.01.2024

How much green tea you need to drink to protect yourself against the flu?

As early as 2011, Japanese researchers reported that drinking 3 cups of green tea daily may drastically reduce the risk of flu. Their human study, conducted among a few thousand schoolchildren, appeared in The Journal of Nutrition.

Study
Researchers from the University of Shizuoka asked 2,663 schoolchildren in January and March how much green tea they drank and how often. They also asked whether the children had been sick with the flu and what the symptoms were. Finally, the researchers used an antigen test to determine whether the children had actually been infected with an inluenza virus.

Results
The researchers found that school children who drank green tea 6 or 7 days a week were 37-40 percent less likely to get the flu.

Clinical influenza = according to doctors, children had the symptoms of influenza; confirmed influenza = antigen test confirms the doctors' diagnosis.

Click on the tables for a larger version.

In addition to the frequency, the number of cups of green tea was also a factor. The table above tells that the study participants who consumed 3-5 cups of green tea per day reduced their risk of flu by 50-60 percent. A higher intake did not reduce the risk of influenza.

Mechanism
The Japanese speculate that the catechins in green tea thwart the influenza virus in several ways.

One mechanism is that catechins attach to hemagglutinin molecules. This allows the virus to attach itself to tissues, after which it can slip into cells. [Antiviral Res. 2005 Nov;68(2):66-74.]

A second mechanism is that the same catechins improve the activity of gamma-delta T cells. This website already reported about this [***coughing modestly***] 15 years ago.

Finally, green tea catechins - especially catechins with a galloyl group - inhibit the enzyme RNA polymerase of the influenza virus. [PLoS Curr. 2009 Oct 13:1:RRN1052.] This enzyme ensures that the viral genome can reproduce itself in the cell.

Source:
J Nutr. 2011 Oct;141(10):1862-70.

More:
Green tea protects against colds and flu 12.02.2009

Archives:
Tea extracts, green tea, black tea
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