Might a delicious cup of freshly brewed tea provide another reason to avoid dairy? Milk may interfere with the health benefits of tea.
I have family that are so stubbornly dependent on milk that they insist on buying a carton to lighten up their coffee every time they come over. If they were tea drinkers, I might have more than just an ethical argument against this practice: milk might well negate the health benefits of tea.
Tea has a host of healthy antioxidants associated with protection against the damage caused by free radicals, which can lead to trouble clotting, atherosclerosis and cancer. Research shows correlation between heavy tea drinkers and lower risk of heart disease, stroke, lower LDL (“bad”) cholesterol and lower rates of some types of cancer. Tea is heart healthy at least in part due to its ability to lower blood pressure and improve blood flow. These benefits are not insignificant from a public health point of view, especially given that tea is the second most consumed beverage around the world, beaten only by water.
There is a debate within the scientific community about how milk protein may affect absorption of the beneficial compounds in tea, called polyphenols. The major protein in milk, casein, is highly flexible and binds to these compounds. Some scientists think this doesn’t really matter, particularly in the small amounts that milk is used in tea . Other scientists think this binding inhibits your body’s ability to absorb a significant percentage of the compounds you could be getting from your cuppa.
Not all teas have equal antioxidant content. Although black, green, oolong and white teas all come from different preparations of leaves from the same plant, camellia sinensis, black tea goes through an oxidation process that may destroy some of the compounds. One important compound, epigallocatechine gallate (EGCG), is found in much greater abundance in green tea than in black, which is the reason it is more often studied for its health benefits. However, there are also many respects in which all teas share similar levels of beneficial antioxidants, and some compounds–like thearubigins and theaflavins—are found in greater quantities in black tea.
To further complicate the picture, there is evidence that the kind of milk you use matters, particularly in regard to fat content. One study of black tea found that skim milk reduces the antioxidant profile by as much as 25% percent, but that higher fat milks (like whole or 2%) decrease absorption by as little as 7% . It isn’t clear why this trend exists, but it is possible that greater fat content interferes with the effect protein has in the stomach. No matter what the type of milk, here’s a plausible hypothesis of how protein affects polyphenols:
the addition of protein increases the pH of the stomach resulting in a reduced absorption of catechins and affects the weak acid compounds of the polyphenols. Polyphenols are easily absorbed in their non-ionized form, but a rise in stomach pH increases the ionization thereby impeding the passage of the polyphenols through the gastric mucosa. 
Whatever the reason for this malabsorption, milk seems to negate the improvements in circulation seen by the straight tea drinkers. This is important for public health, particularly relevant for tea drinkers in United Kingdom, who drink large quantities of tea, but usually douse it in milk . The U.K. has high rates of heart disease and it’s plausible that they aren’t benefiting from the protective effects of their tea consumption.
Still, other researchers disagree. There are also studies that find similar levels of antioxidant activity in tea with milk drinkers as opposed to straight tea drinkers. Alan Crozier of the University of Glasgow in Scotland told NPR that “there’s no convincing evidence that milk is a problem.” He thinks that the binding is reversible and that absorption probably isn’t affected . One of the frustrating things about science, particularly in communicating science, is that it defies easy narrative summary.
In fact, to really turn the dominant narrative on its head, the lead researchers on a 2013 study from University of Guelph, Ontario Canada call milk “an ideal platform for the delivery of bioactive compounds” . The compound they were interested in was none other than EGCG, the major catechin found in green tea. The researchers were interested in this compound for its ability to reduce colon cancer cell proliferation and were hoping to use milk to increase the bioavailablity of EGCG. The researchers extracted EGCG from green tea and encased it either in aggregated milk protein molecules, known as casein micelles, or in water. With low concentrations of EGCG, milk was far superior in reducing cancer cell proliferation .
Motivated reasoning or not, I can identify a few reasons to be skeptical about the above research. The first is that this difference is only found in low concentrations of EGCG. With medium and high concentrations of EGCG, milk and water did equally well. Is it clear that this presents a useful advantage? The second reason is that this is highly experimental research, occurring mostly in petri dishes. Human experimental studies have not demonstrated a benefit to delivering EGCG in casein micelles, although the researchers later had encouraging results testing on “an in vitro digestion model mimicking the gastric and duodenal phases of the human gastrointestinal tract,” or an artificial stomach . Still we are looking at in vitro (in the glass) not in vivo (in life). A third reason is that it isn’t clear to me that the bond created by pouring milk in green tea is equivalent to the bond created by the casein micelles in the lab, nor do the researchers seem especially interested in making this claim. A final note on this study that I can’t help but note is that it is funded by the Ontario Dairy Council and published in the Journal of Dairy sciences, which is funded by the American Dairy Association . The question of how much big money taints sciences and its sources is an open one, but this is a necessary, and potentially relevant, disclosure.
The research may not be absolutely clear cut, but to be on the safe side, drink your tea sans dairy or with non-dairy creamer. There are a range of vegan creamers from So Delicious, Califia Farms and Silk. There don’t appear to be any studies on these non-dairy creamers (and any studies conducted may only be relevant to the given brand tested), but it is unlikely that these affect the antioxidants in any similar way to dairy. Coconut and almond milk have far less protein than milk, and the protein they do have isn’t casein, which has this peculiar tendency to bind to polyphenols.
So, is there anything similar I can say to my aunt and uncle about their coffee and milk habit? Are there any benefits to coffee that are negated by dairy? As usual the research is also mixed, with at least one study finding higher bioavailability of the antioxidant CQA for the black coffee crowd, but the preponderance of evidence suggests that it doesn’t matter either way . I’ll have to stick with my arguments about food waste and cruelty to dairy cows.
Perhaps people will drink their beverages the way they want to no matter what science tells them. In truth, there are only a few studies concentrating on the effect milk has on black tea, which is where the real public health issue lies. The rest of the research focuses on green tea, which has the all important EGCG compound, but my question is–antioxidant concerns aside—why put milk in green tea anyway?
Davis, J. L. (n.d.). Antioxidants in Green and Black Tea. WebMD. Retrieved September 07, 2017
Ungar, L. (2013, April 1). Tea’s health benefits boost its popularity. The Washington Post. Retrieved September 07, 2017.
 this “binding” is formally called non-covalent cross-linking as explained by:
Hursel, R., & Westerterpe-Plantega, M. S. (2011). Consumption of Milk-Protein Combined with Green Tea Modulates Diet-Induced Thermogenesis. Nutrients, 3(8), 725-733. Retrieved September 07, 2017.
Reddy VC, Vidya Sagar GV, Sreeramulu D, Venu L, Raghunath M. Ann (2005). Addition of milk does not alter the antioxidant activity of black tea. Nutrient Metabolism, 2005 May-Jun; 49(3):189-95. Retrieved September 07, 2017.
Hollman PC, Van Het Hof KH, Tijburg LB, Katan MB (2001). Addition of milk does not affect the absorption of flavonols from tea in man. 34(3):297-300. Retrieved September 07, 2017.
 Ryan, Lisa & Petit, Sébastien. (2010). Addition of whole, semiskimmed, and skimmed bovine milk reduces the total antioxidant capacity of black tea. Nutrition research (New York, N.Y.). 30. 14-20. 10.1016/j.nutres.2009.11.005. Retrieved September 07, 2017.
Lorenz M, Jochmann N, von Krosigk A, Martus P, Baumann G, Stangl K, Stangl V (2007) Addition of milk prevents vascular protective effects of tea. Eur Heart J. (2):219-23. Retrieved September 07, 2017.
 Arts, M. J., Haenen, G. R., Wilms, L. C., Beetstra, S. A., Heijnen, C. G., Voss, H., & Bast, A. (2002). Interactions between Flavonoids and Proteins: Effect on the Total Antioxidant Capacity. Journal of Agricultural and Food Chemistry, 50(5), 1184-1187. doi:10.1021/jf010855a
 For the curious, white tea undergoes the least treatment of any leaves and has a similar health profile to green tea. Black tea is fully oxidized, meaning it is left out to dry, torn into smaller pieces and heated up to finish the oxidation process. Oolong sits in the middle between green and black tea.
 Daniells, Stephen. (2010). Milk’s Fat Content May Influence Tea’s Antioxidants. Retrieved September 07, 2017.
 Aubrey, Allison. (2012). Health Benefits of Tea: Milking It or Not. Retrieved September 07, 2017.
 This citation is for the press release. The actual study is cited below.
Elsevier (2013) A New Role for Milk: Delivering Polyphenols with Anti-Cancer Activity. Retrieved September 07,2017
 S. Haratifar, K. A. Meckling, and M. Corredig. (2013) Antiproliferative activity of tea catechins associated with casein micelles, using HT29 colon cancer cells, Journal of Dairy Science, Volume 97, Issue 2 (February 2014), http://dx.doi.org/10.3168/jds.2013-7263, published by Elsevier. Retrieved September 07, 2017
 S. Haratifar, K. A. Meckling, and M. Corredig. (2014). Bioefficacy of tea catechins encapsulated in casein micelles tested on a normal mouse cell line (4D/WT) and its cancerous counterpart (D/v-src) before and after in vitro digestion. Food & Function. 5, 1160-1166 DOI: 10.1039/C3FO60343A
 Duarte, GS & Farah, A. (2011).Effect of simultaneous consumption of milk and coffee on chlorogenic acids’ bioavailability in humans. J Agric Food Chem. 2011 Jul 27;59(14):7925-31. doi: 10.1021/jf201906p. Epub 2011 Jun 15.
 JP (2010) Coffee Milk Controversy. Retrieved September 07, 2017.