Do milk proteins cancel the healthy benefits from nutrients in tea?
To many, the most well-known nutrients in tea are antioxidants. Antioxidants are molecules that effectively react with unstable free radicals before it can damage one’s DNA. It is because of this effect that antioxidants are known to reduce the risk of cancer. However, how one drinks their tea is culturally determined and some have hypothesized that some brewing methods and addition of additives like milk and sugar can cancel out the benefits of antioxidants.
This paper is a brief review of relevant scientific work to address whether or not adding milk or sugar to tea can make the health benefits from drinking tea obsolete.
The interactions between tea antioxidants and milk proteins has been studied since 1963, when it was concluded that milk proteins can bind to tea antioxidants. Since then, other studies have confirmed this conclusion. Because of this milk protein and tea antioxidant binding, many fear that the common (and delicious!) practice of adding milk to tea destroys antioxidants in tea. To test this hypothesis, many scientists have conducted in vitro (out of body) and in vivo (in the body) experiments. In vitro studies commonly used simulated models of the human digestive system to digest tea antioxidants with or without milk. Researchers then took the digested tea or milk tea and added it to a colony of cancer cells (HT29) and had their rate of growth measured. The cancer cell colonies that were exposed to both tea and milk tea had their growth inhibited at similar levels at antioxidant concentrations (0.03 mg/mL) and above (Haratifar 2014). This research may have a conflict of interest since it was funded by the Ontario Dairy Association.
A similar study conducted by Unilever concluded that antioxidants bound to milk proteins were just as bioavailable as unbound antioxidants by measuring antioxidant levels of tea and milk tea after three different stages of digestion (van der Burg-Koorevaar 2011). But again, these findings are suspect since Unilever is a British-Dutch consumer goods company that could benefit from calming fears over milk tea antioxidant levels.
In 2001, a research division in the Netherlands equivalent of the FDA conducted an in vivo study on antioxidant levels in human blood plasma after consuming tea or milk tea. They concluded that drinking both tea and milk tea resulted in similar levels of blood plasma antioxidants (Hollman 2001). Another 2001 study conducted by a food and nutrition company, it was reported that both tea and milk tea digestates inhibited the activity of a known mutagen in a bacterial colony at similar levels (Krul 2001).
There are some drawbacks to having tea with milk. One in vitro and in vivo study concluded that milk counteracted the beneficial vascular activity of tea (Lorenz 2007). This study was followed up by an in vitro study in 2009 using soy milk instead and reached a similar conclusion (Lorenz 2009). Another study found that consuming green tea helped subjects undergo diet induced thermogenesis (in other words, they burned more calories at a resting heart rate after drinking green tea), consuming green tea with milk had no such effect (Hursel 2011).
All in all, this topic does not have a clear scientific consensus, as is with most foods (like, are eggs good for you or bad for you this year??). That said, scientists do in fact agree that casein proteins that are present in milk do bind to tea antioxidants. Caseins are a particular type of protein that is produced by mammals so it should be absent in soy, almond, and oat milk.
Soy milk has almost as much protein as milk and some of these proteins are suspected to behave similar to casein in binding tea antioxidants. So if you want to ensure you get the most antioxidants out of your tea, I suggest having a green tea with an alternative milk that is low in protein, such as almond milk. Oat milk will have more protein than almond milk, but less than regular milk or soy.
by Stephen Lo, Bobarista and Masters in Chemistry candidate, USF
1. Krul C., Luiten-Schuiten A., Tenfelde A., van Ommen B., Verhagen H., Havenaar R. Antimutagenic activity of green tea and black tea extracts studied in a dynamicin vitro gastrointestinal model. Mutat. Res. 2001;474:71–85.
2. Lorenz M., Jochmann N., von Krosigk A., Martus P., Baumann G., Stangl K., Stangl V. Addition of milk prevents vascular protective effects of tea. Eur. Heart J. 2007;28:219–223.
3. Lorenz, Mario, Karl Stangl, and Verena Stangl. "Vascular effects of tea are suppressed by soy milk." Atherosclerosis 206.1 (2009): 31-32.
4. Haratifar, S., K. A. Meckling, and M. Corredig. "Antiproliferative activity of tea catechins associated with casein micelles, using HT29 colon cancer cells." Journal of dairy science 97.2 (2014): 672-678.
5. van der Burg-Koorevaar, Monique CD, Silvia Miret, and Guus SMJE Duchateau. "Effect of milk and brewing method on black tea catechin bioaccessibility." Journal of agricultural and food chemistry 59.14 (2011): 7752-7758.
6. Hollman P.C., van het Hof K.H., Tijburg L.B., Katan M.B. Addition of milk does not affect the absorption of flavonols from tea in man. Free Radic. Res. 2001;34:297–300
7. Hursel, Rick, and Margriet S. Westerterp-Plantenga. "Consumption of milk-protein combined with green tea modulates diet-induced thermogenesis." Nutrients 3.8 (2011): 725-733.