Even the unabsorbed antioxidants of green tea may be good for you. (Photo by mckaysavage)
So far in the series of posts about green tea and antioxidants we've seen that green tea significantly increases antioxidant activity in human plasma and that it does so even when milk is added. Black tea has a similar but slightly smaller effect.
I stumbled upon a somewhat older paper by Benzie et al. who were among the first to study how well antioxidants from green tea are absorbed by humans. In their own words:
However powerful the in vitro anticarcinogenic activity of tea antioxidants may be, potential health benefits are unlikely to be realized if tea antioxidants are inactivated in the gut or are not absorbed.
We already know from other studies that something in green tea has to be absorbed, because the results are so overwhelmingly positive, but whether it's the antioxidants or something else that is behind the health benefits of tea is a different question.
Strong green tea and peak increases in antioxidant activity
To make the tea used in the study, 500 ml of boiling water was poured on 20 grams of green tea leaves (8-10 tea bags), and the tea was then allowed to infuse for 10 minutes. That makes for a very strong tea, much stronger than the ones used in the other studies. The volunteers drank 300-400 ml of the tea, after which blood samples were collected at different time intervals.
Once again, green tea caused a significant increase in plasma antioxidant activity. The peak increase occurred 20-40 minutes after ingestion. The mean increase at 40 minutes was 4%. The result is very similar to the one I wrote about in my previous post: the method of measuring antioxidant activity was the same in both studies, and as the tea was much stronger in this one, a more significant increase is logical.
Interestingly, though, there was no difference between the participants who consumed 400 ml of green tea and those who consumed only 300 ml (due to the bitter taste). The authors suspect that this may be due to the absorption mechanism being saturated at the lower dose; this may mean that it's better to spread your daily 10 cups of green tea throughout the day instead of drinking it all at once.
In the figure above, the circles represent plasma antioxidant values measured in the controls, who were given only water. The squares represent the tea drinkers. The subjects were the same in both groups, with at least four weeks between the two experiments.
The authors seem a little disappointed that the antioxidants in tea are rather poorly absorbed. On the other hand, they point out that the antioxidants that are not absorbed in the gut may conserve other antioxidants from food and thus have a local protective effect. This might help explain some of the many health benefits of green tea.
Strongly brewed green tea increases plasma antioxidant activity in humans by up to 4%. The effect lasts at least two hours, but the most significant increase is seen 20-40 minutes after ingestion.
For more information on green tea and black 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