Adding a dash of milk to your tea may retain its antioxidant effect after all. (Photo by floluong)
I wrote in my previous post about a study that suggested 2-3 cups of green tea raises antioxidant concentrations in plasma of healthy subjects, both male and female. Any less than that didn't have a noticeable effect on plasma antioxidants.
I also mentioned I'll be looking at other papers studying the relationship between tea and antioxidants, so here goes.
Green tea, black tea and antioxidants in humans
The results were reproduced by Leenen at al. who found that tea, green or black, increases antioxidant activity in plasma. The authors gave 21 healthy volunteers a single dose of tea. The dose refers to 2 grams of freeze-dried tea solids in 300 ml of water. According to the authors, this is equal to about three cups of tea (when I first looked at the study I made the mistake of assuming 2 grams of ordinary tea leaves was used; however, this is not the case).
This is an interesting study, because both green tea and black tea were studied, and both were studied with or without the addition of milk. Mineral water was used as control. In a cross-over design, each volunteer received the six possible combinations (green or black tea or water with or without milk) on six different days with at least two days in between treatments. For the milk treatments, 60 ml of pasteurised full-fat milk was used.
After an hour of drinking green tea without milk, antioxidant levels rose from 1.144 to 1.178 mmol/l, an increase of 0.034 mmol/l. With milk added, concentrations increased from 1.132 to 1.167 mmol/l, the difference being almost the same, 0.035 mmol/l. After two hours, the increases were 0.032 and 0.024, respectively.
After an hour of drinking black tea without milk, antioxidant concentrations rose from 1.147 to 1.170 mmol/l, an increase of 0.023 mmol/l. When milk was added, the increase was from 1.122 to 1.141 mmol/l, the difference being 0.019 mmol/l. After two hours, the increases were 0.015 and 0.006 mmol/l, respectively.
When water or water and milk were used, no similar increases in antioxidant concentrations were seen.
So what can we say about these numbers? Clearly, both green tea and black tea increased plasma antioxidant concentrations, regardless of whether milk was used or not. Green tea increased the antioxidant concentrations of plasma more than did black tea. Adding milk to either black tea or green tea still caused an increase, but after two hours, the increase was smaller than without milk.
Comparing the results with other studies
Comparing these results to the ones I wrote about in the previous post, we can see that the effect here was similar but more modest. In the study by Sung et al., one hour after drinking three cups of green tea the increase in antioxidant concentrations was 12%, and after two hours, it was 12.7%.
In this study, the increase after one and two hours of drinking green tea was about 3%. When milk was added to green tea, the increase was 3% after one hour and 2% after two hours. After one and two hours of black tea, the increases were 2% and 1.2%, respectively. When milk was added to black tea, the numbers were 1.7% and 0.5%.
The variation between the results from the two studies may be due to differences in preparation of the teas and methods of measurement.
3 cups of green tea or black tea increases plasma antioxidant concentrations in healthy humans by up to 2-3%. When pasteurised full-fat milk is added, the effect is slightly diminished but still noticeable.
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