It appears that proteins in milk bind to some of the substances present in tea, leading to a vast reduction of their beneficial effects.
The researchers asked healthy women volunteers to drink either freshly brewed 500 ml of black tea, black tea with (skimmed) milk, or boiled water as control.
Studies showed that drinking tea with milk was no better than drinking water.
Their blood vessels (arteries) were monitored before and continually after they drank, for two hours using high- resolution ultrasound measurements. Black tea was found to relax the vessels significantly while water did nothing.
This result confirms many earlier studies, which have suggested that drinking tea is beneficial to, among others, the cardiovascular system.
The surprise came when they monitored the blood vessels of women who drank tea with milk. Drinking tea with milk was no better than drinking water!
The first author of the paper, Dr. Mario Lorenz, is reported to have said: "We found that whereas drinking tea significantly increased the ability of the artery to relax and expand to accommodate increased blood flow compared with drinking water, the addition of milk completely prevents the biological effect. To extend our findings to a functional model, we determined vasodilation (relaxation of blood vessels) in rat aortic rings by exposing them to tea on its own and tea with individual milk proteins added, and got the same effect".
In other words, the proteins in milk are the benefit-killers here. The researchers theorise that these proteins bind to the biologically active ingredients of tea, making them unavailable for action.
These ingredients belong to what is called the catechin class of molecules. Their names have a chant-like intonative or rhythmic ring to them: catechin, epicatechin, gallocatechin, epigallocatechin, catechin gallate, epicatechin gallate, gallocatechin gallate, and epigallocatechin gallate.
The name catechin comes from its origin in tropical plants (catechu), and the family belongs to the class of flavonoids, since these molecules are responsible for the flavour. Catechinoids have been shown to offer a variety of health benefits. They are good anti-oxidants and anti-inflammatory agents, and protect cells from general wear and tear.
They are thus helpful against age-related disorders such as cataract and some retinal diseases of the eye, cardiovascular and neuromuscular disorders. They activate some enzymes that help relax blood vessels. There is also some evidence of their anti-cancer activity. In short, tea catechinoids have multivalent health benefits.
The Chinese, who introduced it to the world two millennia ago, have always held that tea is an all-purpose tonic. They consume two varieties: green tea and oolong, which is prepared by mild fermentation of green tea. The rest of the world uses black tea; we in
Black tea too has the catechins slightly modified; heating in the CTC step generates tannins; hence the darker colour (and also the unpleasant sour after-taste upon boiling it in water).
Tannins are not that healthy; they bind to the iron and other micronutrient metals in the diet, and remove them from circulation (so, do not overboil your tea, nor overdrink it). The lighter hued green tea and oolong, free of tannins, are safer. Tea came to
The late Dr. K. T. Achaya remarks in his "A Historical Dictionary of Indian Food" (OUP, 1998) that I Ching, a Chinese traveller in
While the Orientals drink tea straight, people in 17th century
Gujaratis make tea with milk and add ginger; they also make a special masala, a pinch of which is added while making tea.
Adding milk to tea seems to have come from the colonial British ad Dutch. The other more popular way to drink tea is to add lemon or lime rather than milk.
Synergy and dysergy
That the added milk acts as a confounding factor tells us another thing, namely the effect of one component on that of another in a mixture.
Traditional medicine differs from allopathy or molecular medicine in that it more often than not uses multi-component mixtures as extracts.
In a mixture, component A might be the one that confers benefit; what each of the other components (B, C,…) does — enhance or confound the benefit — is an issue that needs study.
A substance that enhances the effect of another is said to act in synergy, while that which decreases this effect is said to act in dysergy.
Put it another way. Now that the
Adding lemon juice to black tea lightens the colour; does it modify the effects of the catechinoids?
What are the effects of added butter, salt, ginger, cardamom, the Gujarati masala and other spices? Here is a nice little summer project for a student!
Let us not forget coffee, the morning staple of many in peninsular
Does added milk synergise or dysergise? Are the Americans, Eastern Europeans and the Turks wiser in drinking it black and thick?
Some papers claim, however, that the cholesterol-lowering effect of coffee is not affected by added milk. Can this be confirmed? Add this as another aim of the summer project.