Wednesday, February 4, 2009

Drinking 3 Cups of Green Tea Increases Plasma Antioxidant Activity in Humans by 12%

Green tea has an antioxidant effect in vivo
The antioxidant effect of green tea lasts at least 2 hours. (Photo by modomatic)

Antioxidants have been all over the media in the past few years. Even people who have no idea what antioxidants are know that they're something positive. Green tea has also had more than its fifteen minutes of fame (this blog is just one example). Unsurprisingly, the health benefits of green tea are often attributed to its antioxidant activity.

The truth, however, is more complicated. Studies done in vitro (literally "within the glass") certainly give us a clue on what green tea does, but the human body is more complicated. The fact is that we're still not exactly sure what happens when people drink green tea.

That's why I'm going to review some of the studies comparing the in vitro and in vivo (literally "within the living") effects of green tea. Specifically, I will be looking at studies related to the antioxidant activity of green tea and other teas.

Green tea and antioxidants in human plasma

The first one is by Sung et al. In the study, the authors gave 10 healthy subjects of both sexes green tea and measured the amount of antioxidant capacity in their plasma.

This is a particularly interesting study not only because the subjects were humans but also because the amounts of green tea were small. So small, in fact, that I for one drink more green tea almost every day than the subjects did when consuming the highest dosage.

In the first week, the subjects drank 150 ml of green tea made by boiling 2.5 grams of dried green tea leaves in 80°C for 2 minutes. That's pretty close to one tea bag in one cup of water. In the second and third weeks the amount was doubled and tripled, respectively.

green tea and antioxidant activity
After one hour of ingesting 150 ml of green tea, the plasma antioxidant concentrations of the subjects increased to 1.33 mmol/l. After two hours, the concentration was 1.34 mmol/l. Compared to baseline levels of 1.31 mmol/l, the increases were 0.02 and 0.03 mmol/l.

In the second week, drinking 300 ml of green tea increased antioxidant concentrations from 1.29 to 1.38 mmol/l after one hour and 1.37 mmol/l after two hours. Thus, even though the increase was more significant than with the lower dose, there was a slight decrease after two hours compared to levels measured after the first hour.

After the third week, when the amount was 450 ml of green tea, antioxidant concentrations increased from 1.33 to 1.49 mmol/l at 1 hour and 1.50 mmol/l at 2 hours.


After drinking one cup of green tea, the increase in the total antioxidant capacity of plasma was not statistically significant. However, one hour after drinking two cups of green tea the increase was 7%, and after two hours the increase was 6.2%. After 3 cups and one hour, the increase was 12%, and one hour later rose to 12.7%.

Based on this study, green tea seems to have an antioxidant effect in humans. The effect is dose-dependent and lasts at least 2 hours.

For more information on green tea, see these posts:

Green Tea Catechin Reverses the Effect of DHT in Prostate Cancer Cells
Caffeine and Polyphenol Contents of Green Tea, Black Tea, Oolong Tea & Pu-erh Tea
How Black Pepper Increases the Bioavailability of the Healthiest Green Tea Catechin
Drinking 10 Cups of Green Tea Daily and Not Smoking Could Add 12 Years to Your Life

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