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12.02.2009

Green tea protects against colds and flu

People who take a daily dose of two capsules containing extracts of green tea [scientific name Camellia sinensis] are protected against colds and flu, researchers at the University of Florida discovered.

The researchers got over a hundred test subjects to take two capsules a day of the supplement ImmuneGuard for three months, or a placebo as control. Each capsule contained 450 mg of green tea and rooibos extracts. Two capsules contain the same amount of active ingredients as ten cups of green tea.

The brain behind ImmuneGuard is Jack Bukowski, according to the ImmuneGuard website. Bukowski also worked on the research described in this article, and on previous studies on the effects of the tea-supplement. Nutraceutical Holdings, the manufacturer of ImmuneGuard, put up the money for the study.

The researchers kept track of how often their test subjects got flu or a cold. The results are shown below.

So the supplement works. The active ingredient in Camellia sinensis is probably the amino acid L-theanine. The compound stimulates a specific category of immune cells – the gamma-delta-T-lymphocytes – to manufacture gamma-interferon in the body. Interferon is what the body makes if it is attacked by pathogens like viruses.

When viruses infect cells and use them as a place to multiply, the body's immune cells warn the healthy cells of the presence of viruses. They do this through interferon, which stimulates the cells' production of the enzyme PKR. This stops viruses from reproducing and the cells die.

In earlier studies the researchers showed that people who drink six cups a day of green tea produce fifteen times more gamma-interferon if they are attacked by bacteria.

Sources:
J Am Coll Nutr. 2007 Oct;26(5):445-52.