Does Milk Impact Tea's Health Benefits?

Tea with milk is so much smoother, less bitter and less astringent—but is it as good for you as tea without milk? 

Teas are bitter and astringent mainly due to the presence ofcatechins and polyphenols, often called tannins. The proteins in milk grab ontothese tannins, thereby preventing them from reaching the receptors forbitterness and astringency in taste buds.⁽¹⁾⁽²⁾ The result is a teathat tastes sweet, creamy and delectable.

But by being bound to milk proteins, are the health benefitsof catechins and polyphenols lost?

To answer this question, we must first explain that catechinsare compounds the tea leaf produces in the field to protect it againstexcessive sun exposure. These compounds absorb the excess energy from the sunthat the leaf's photosynthetic machinery cannot handle and dissipate it asheat. That way the leaf's photosynthetic capacity is protected.

 After the leaf isplucked, a pair of enzymes called polyphenol oxidases goes to work combiningcatechins together into larger compounds, the polyphenols theaflavin, thearubigin,and theabrownin. Heating destroys polyphenol oxidases. Green teas that areheated soon after plucking have more catechins and lesser amounts of the largerpolyphenols, while other teas that are allowed to oxidize longer tend to havegreater amounts of the larger compounds. 

 At least two benefitshave been attributed to catechins and polyphenols: an anti-oxidant effect andan effect on blood vessels. 

The antioxidant effect of these compounds may well beexaggerated—even if you were to absorb all of them present in a cup or three oftea they would be a tiny proportion of your body's total antioxidant supply.⁽³⁾Furthermore we don't really know whether increasing antioxidant activityin general is beneficial or not. That said, it is unclear whether adding cow'smilk or other milk to tea has any effect on the tea's antioxidant capacity.^(4)(5)(6)

Garnering interest more recently has been the effects of thesecompounds on blood vessels: they appear to make blood vessels more responsiveto variations in blood flow.⁽⁷⁾ This variation is critical fornormal cardiovascular function. An exercising muscle needs more oxygen. Torespond to this need, your heart rate increases and pumps out more blood perminute in order to deliver the necessary oxygen. At the same time, your bloodvessels expand to accommodate the increased amount of blood per minute goingthrough them.

As we grow older, our blood vessels become "stiff." Theydon't expand as readily to an increase in blood flow reaching them. When theyfail to respond, the pressure in the blood vessels builds up, leading tohypertension and cardiovascular disease. Tea catechins and polyphenols canincrease blood vessel responsiveness through multiple mechanisms that areslowly becoming clear.

 The next question is: Doesthe addition of milk to your tea decrease the effects of its catechins andpolyphenols on your blood vessels? 

 At first the answer hasseemed to be "yes." Mario Lorenz and his colleagues did a simpleexperiment where they gave 16 healthy women tea with and without milk andlooked at blood vessel responsiveness 2 hours later. They found that theirparticipants' blood vessels responded better to plain black tea than to water,but that adding skimmed milk canceled the effects.(8) However, this experimentwas too simple to really test the issue.⁽⁹⁾

One of the problems with this experiment was that casein, amilk protein that binds to polyphenols and catechins, slows down stomachdigestion significantly. It may well be that the effects of tea with milk maynot be seen until well after the two hours that Lorenz and colleagues allowed.The whole point of a normal digestive system is to break down proteins so youcan absorb and use their amino acids and peptides, the building blocks for yourown body's proteins. If your digestive system breaks down proteins that havecatechins and polyphenols attached, these compounds should be free to beabsorbed.⁽¹⁰⁾ It just takes time.

Bottom line: Proteins in milk, particularly cow's milk, dobind to catechins and polyphenols, making your tea smoother and moredelectable, but as to whether this binding affects a tea's healthfulness—thejury is still out.

 (1) C.D.Kanakis et al. (2011) Milkβ-lactoglobulin complexes with tea polyphenols. Food Chemistry, 127(3),1046-1055.

 (2) I. Hasni et al. (2011) Interaction of milkα- and β-caseins with tea polyphenols. Food Chemistry, 126(2), 630-639.

 (3) S. B. Lotito and B. Frei. (2006)Consumption of flavonoid-rich foods and increased plasma antioxidant capacityin humans: cause, consequence, or epiphenomenon? Free Radical Biol. Med. 41,1727–1746.

 (4) L. Ryan, L. and S. Petit. (2010) Additionof whole, semiskimmed, and skimmed bovine milk reduces the total antioxidantcapacity of black tea. Nutr. Res. (N.Y.) 30, 14–20.

 (5) L. Ryan, and S. Sutherland. (2011)Comparison of the effects of different types of soya milk on the totalantioxidant capacity of black tea infusions. Food Research International, 44(9), 3115-3117.

 (6) S. Dubeau et al. (2010) Dual effect ofmilk on the antioxidant capacity of green, Darjeeling, and English breakfastteas. Food Chemistry, 122 (3), 539-545.

 (7) R.T. Ras et al. (2011) Tea ConsumptionEnhances Endothelial-Dependent Vasodilation; a Meta-Analysis. PLoS ONE 6(3):e16974. https://doi.org/10.1371/journal.pone.0016974(https://doi.org/10.1371/journal.pone.0016974)

 (8) Lorenz, Mario, et al. (2007) Addition ofmilk prevents vascular protective effects of tea. European Heart Journal, 28(2), 219–223. 

 (9) M. Lorenz et al. (2007) Addition of milkprevents vascular protective effects of tea: reply. European Heart Journal,28(10), 1266–1267.

 (10) M. van der Burg-Koorevaar, et al. (2011) Effect of Milk and Brewing Method on Black Tea Catechin Bioaccessibility. J. Agric. Food Chem. 59, 7752–7758. 

(11) Ref.: Jeong-a Kim et al. Epigallocatechin Gallate, a Green Tea Polyphenol, Mediates NO-dependent Vasodilation Using Signaling Pathways in Vascular Endothelium Requiring Reactive Oxygen Species and Fyn J. Biol. Chem. 2007 282: 13736-. doi:10.1074/jbc.M609725200;M. M. Lorenz et al. Green and black tea are equally potent stimuli of NO production and vasodilation: new insights into tea ingredients involved. Basic Res Cardiol. 2009 Jan;104(1):100-10. DOI: 10.1007/s00395-008-0759-3.

(12) Ref.: E. Jöbst et al. Noncovalent cross-linking of casein by epigallocatechin gallate characterized by single molecule force microscopy. J Agric Food Chem. 2006 Jun 14;54(12):4077-81. DOI: 10.1021/jf053259f (https://doi.org/10.1021/jf053259f) Diagram Copyright 2019 Virginia Utermohlen, used with permission.