I’m a tea drinker who enjoys tea with a little bit of milk. Not only does it add a nice creamy texture to the tea, it also seems to take the bitter edge off, even without adding any sugar. And I’m certainly not alone – by one estimate, 98% of British tea drinkers top off with the white stuff.
In my previous post I looked into some of the health benefits of green tea, and found the evidence to be somewhat limited. This isn’t so surprising, given the difficulty of determining the effects of one small part of a large, complex diet. So is it folly to try to understand how the combination of two foods, milk and tea, might affect health? Maybe so, but there is some evidence out there, and the news isn’t so good.
In 2007, Verena Stangl and colleagues published an article in the prestigious European Heart Journal entitled “Addition of milk prevents vascular protective effects of tea.” This study was based on a legitimate observation – if the British drink so much tea, why is cardiovascular disease still so prevalent? The researchers knew that tea causes relaxation of the aorta, a physiological mechanism associated with health (stiff blood vessels cause all sorts of problems).
They then devised a simple experiment – have subjects drink 1) straight tea, 2) a combination of 90% tea and 10% milk, or 3) hot water. By popping on an ultrasound probe on the subjects, they could then see what happened to the aorta. The experiment was small but the results were not – the folks who had milk in their tea had an aorta just as stiff as those who drank hot water. Those who had straight tea enjoyed a very relaxed aorta.
Sort of odd, don’t you think? Why would the simple act of adding milk to tea possibly annihilate the beneficial effects? Remember those catechins, especially the star player, epigallocatechin-3-gallate (EGCG)? It would seem that EGCG is pretty promiscuous – it likes to hook up with whatever protein might be around. It especially likes proline, one of the amino acids.
Wouldn’t you know, one of the most abundant proteins in milk, β-casein, is studded with proline. Indeed, when Stangl looked at the various polyphenols in the tea, the EGCG level in the milk/tea combo was only 20% of the plain tea level.
Ok, so easy solution – just switch from cow milk to soy milk, right? Not so fast – glycinin and β-conglycinin, the major proteins in soy, also have a surplus of proline. Look for Stangl’s newest article, coming out soon in Atherosclerosis, showing that soy milk chomps those catechins every bit as much as cow milk.
Bottom Line: There’s a reason tea tastes less bitter after adding milk – all the catechins just got bound up! If you want to enjoy all the catechins you possibly can, best to have the tea like nature made it – straight up.