Wednesday, August 21, 2013

Milk, Tea & Honey - Two Things Don't Belong: Milk & Sugar Potently Reduce Antioxidant Effects of Green & Black Tea

Chi Latte is a sugar bomb, but no healthy, antioxidant beverage.
Over the past couple of weeks it has become relatively quiet in the "tea is good for your health", "tea makes you lose weight magically", "tea reduces diabetes risk", etc. column of the science news here at the SuppVersity, and in general. Ok, you still got your daily "green tea reduces inflammation study", but let's face it. That's boring.

What is interesting, however, are the results of a recent study that's about to be published in Food Chemistry (Korir. 2013). In this very paper, a group of researchers from the Egerton University in Kenya, the Association for Strengthening Agricultural Research in East and Central Africa in Uganda and the Tea Research Foundation of Kenya report that...

Adding milk or sweeteners to your tea will reduce its antioxidative capacity

And the effects the researchers observed in vitro and in vivo, were pretty significant, as you can see in the data I plotted for you in figure 1 & 2:
Figure 1: Antioxidant activity of green and black with different milk concentrations. No sweetener added (Korir. 2013)
Now, the first question I had, when I glimpsed at the results was "wtf. of course will the antioxidant effects of tea decrease in response to a decrease in the amount of tea per volume of liquid decreases"; I mean, that's exactly what happens when you add 10% of milk to your cup of tea at home. It becomes "dilluted" (usually you would not use that term if you put milk into something, but that's what it is). Now, the obvious question is: Was that even the case? Let's take a look at what the methods section of the paper can tell us:
Based on the results of the study at hand, we cannot really say whether adding milk to your tea after brewing it will reduce its antioxidant capacity. Luckily we do have data from a previously conducted 2011 study by Ryan et al. I wrote about in July 2011 that confirms: Adding milk after brewing reduces the FRAP (measure of antioxidant activity) value of tea more than the same amount of water does | read more
"Each infusion was prepared by infusing five grammes of coarse tea samples in 100ml of boiling distilled water in a 100ml volumetric flask and stirring with a magnetic stirrer on a hot plate for 10 minutes. Tea infusions with milk were made using 5g of tea and different concentrations of milk (2%, 4%, 6%, 8%, 10%, 20% and 40% (v/v milk/water). Infusions with milk and sugar were brewed with 3g and 10g of sugar plus the several concentrations of milk, and those with milk and stevia (0.1g and 0.3g) wereprepared. Similarly, teas with several concentrationsof milk plus 3g and 10g honey were prepared. All the above tea infusions were strained through cotton wool to remove the tea particles and left to cool to room temperature [before the antioxidant activity of the] prepared tea extracts was determined using the 2, 2’-diphenyl-1-picryhydrazyl radical (DPPH) method." (my emphasis in Korir. 2013)
I guess, you will already have gotten it, right? By adding the milk before the brewing, the scientists did manage to get around the dilution effect, but at the same time they reduced the practical relevance of their results to zero. Why? Well, do you brew your tea with the milk already in it? I don't think so... so if it were not not for the 2011 study by Ryan et al. I would say: The verdict on milk is still out there. With the pertinent results from the Ryan study, however, you can be assured that adding milk to your tea makes it a less potent ROS scavenger.
Figure 2: Mean values of antioxidant activity of sweetened plain black tea (Korir. 2013)

Obviously, the same limitations also apply to the real-world significance of the effects of pre- vs. post-addition of sugar, honey and stevia (see figure 2), of which the scientists suspect that they may be a result of
"[c]omplex compounds, such as pentagalloylglucose (PGG), tetragalloylglucose (4GG) and trigalloylglucose (3GG) [that] are likely to be formed as glucose interacts with the gallic acid in tea where by the glucose hydroxyl groups are serially substituted by gallic acid." (Korir. 2013)
These glucose complexes would then bind with the bovine serum albumin and other proline-rich proteins present in milk and thus alter the biological activity of tea molecules (Chitpan. 2007).

So why is honey the worst then?

Honey has been shown to possess significant antioxidant activity of its own. The latter is ascribed to the presence of compounds such as chrysin, pinobanksin, vitamin C, catalase, and pinocembrin that are thought to function as antioxidants (Valentini. 2010). We would therefore actually expect to see an increase in antioxidant activity, when we put honey into our teas, right? So what's the reason that the exact opposite happens and that honey was found to be the most inhibiting sweetener in both plain and black teas with milk? The answer is: We don't know.
What we do know, however, is the fact that we are actually not interested in the mere presence of maximal amounts of antioxidants in tea, but rather in their biological effects on the antioxidant defense system of our bodies; and the correspoding image that emerges based on the accompanying rodent study is more complex than the in vitro data would have suggested:
Lack of drive? Theacrine will get you going | read more
"The highest levels of GSH were recorded in plasma after 2 hours of tea consumption. The GSH levels due to various types of tea differed significantly (p<0.001) in the same tissue at different time intervals [...]. Highest GSH levels were recorded for black tea fortified with 2% milk in plasma, as compared with the other teas. However, in kidney and brain tissues, higher GSH levels were recorded for plain black teas after 2 hours and 4 hours of tea consumption, respectively. The GSH levels in the liver were similar to those in the brain but the peak in the liver was after 30 minutes." (Korir. 2013)
Now, while there is still no place for sugar in your tea, the reputation of milk is partly restored - but only if it's used in very tiny amounts. The Chi Latte you see in the head of this article still remains "the soda among the teas" and looking at the photograph I would assume that the effect of this particular incarnation of "sugar milk with a splash of tea in it", is probably more detrimental to your health than a whole bottle of Coke.

Catechin content of the leaves of green, oolong, black & pu-erh tea
Bottom line: Drinking tea is more than just a means of getting your antioxidants in. Against that background I am hesitant to suggest that everyone must drink his/her tea without milk and sugar, even if he/she hates the taste.

Nevertheless, cutting back on the amount of milk (<2%) and switching from honey or table sugar to stevia (and probably most other forms of artificial sweeteners) would be something to consider, if you want to make sure that the tea works its maximal antioxidant magic in your blood and organs.

  • Chitpan M, Wang X, Ho CT, Huang Q. Monitoring the binding processes of black tea thearubigin to the bovine serum albumin surface using quartz crystal microbalance with dissipation monitoring. J Agric Food Chem. 2007 Dec 12;55(25):10110-6.
  • Korir MW, Wachira FN, Wanyoko RM, Ngure RK. The fortification of tea with sweeteners and milk and its effect on in vitroantioxidant potential of tea product and glutathione levels in an animal model. Food Chemistry. 2013 [accepted manuscript]