Time Out – Does Milk Ruin Tea Time?

Posted on September 22, 2012

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For centuries, certain cultures have customarily added milk to fresh-brewed tea – but in recent years, scientists in laboratories around the world have been “hotly” debating whether this seemingly-benign practice may actually inhibit some of the already well-established health benefits of tea drinking.

The topic arose recently in the oncology clinic (of all places), when my mentor shared findings published by the Mayo Clinic that called for clinical trials of green tea compounds after observing that some of their lymphoma patients experienced clinical responses with supplementation.  Until the jury is out, he will continue to recommend green tea consumption to his patients – but I decided to take this opportunity to brush up on the milk-in-tea debate.

It has been proposed that proteins in cow’s milk form complexes with the biologically active compounds in tea, and either inhibits their absorption or impairs their activity in the body (and unfortunately there is evidence that soy milk does the same).  As is often the case in nutrition science, findings to date have been equivocal, with some researchers endorsing the theory as others dismiss it.

Probably the best paper to date that I have read on this issue is one from the European Heart Journal in which researchers tested both the in vitro and in vivo effects of milk on tea.  They concluded, with good reason, that milk does in fact impair at least some of the many biologically active compounds in brewed tea.

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Addition of 10% milk significantly impairs the vasodilatory effects of tea in 16 healthy female volunteers.

The researchers also tested the “milk protein hypothesis” and incubated endothelial cells along with tea and various isolated milk proteins, again demonstrating that the casein proteins appear to be the culprits.

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Caseins are the primary inhibitors of vasoactive tea compounds.

Also examined was the effect of milk on various tea constituents.  Clearly demonstrated are greater than fivefold reductions in ECG & EGCG, two compounds found in green tea and shown in a multitude of studies to have beneficial health effects (and as a result, they are now marketed in many over-the-counter green tea & weight-loss supplements).

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Milk sequesters several biologically active tea compounds, but has no significant effect on methylxanthines (caffeine and theobromine).

The authors believe these conclusions support both the lack of beneficial effects of tea on heart disease observed in populations from the UK, as well as the lack of antioxidant benefits observed in milk chocolate versus dark chocolate.

At this point, you may be wondering if there are any benefits whatsoever of adding milk to tea, and in fact there are.  Research has shown that absorption oxalate, a compound primarily found in black teas that can contribute to the development of kidney stones, is inhibited by the addition of milk to tea (likely a result of the calcium content of milk).  Adding cold milk to tea also lowers the temperature, and accumulation of thermal damage over time from consumption of hot liquids has been linked to esophageal and gastric cancer.

So if you consume all types, like I do, you may wish to practice moderation:  drink your white and green teas “naked”, save the milk for the black stuff, and let them all cool down a bit before enjoying.

References:

Shanafelt T.D., et al. Clinical effects of oral green tea extracts in four patients with low grade B-cell malignancies.  Leukemia research 1 June 2006 (volume 30 issue 6 Pages 707-712 DOI: 10.1016/j.leukres.2005.10.020)

Noda C., et al.  Induction of apoptosis by epigallocatechin-3-gallate in human lymphoblastoid B cells.  Biochemical and Biophysical Research Communications.  2007  November.  362 (4):  951-7.

Hursel, R.  Consumption of milk-protein combined with green tea modulates diet-induced thermogenesis.  Nutrients.  2011 August; 3(8): 725-733.

Lorenz, M., et al.  Addition of milk prevents vascular protective effects of tea.  European Heart Journal. 2007 January; vol. 28:  219-223.

Hertog MG, et al. Antioxidant flavonols and ischaemic heart disease in a Welsh population of men: the Caerphilly Study. Am J Clin Nutr 1997;65:1489–1494.

Savage GP, et al.  Bioavailability of soluble oxalate from tea and the effect of consuming milk with the tea.  European Journal of Clinical Nutrition (2003) 57, 415–419.

Deandrea S, et al.  Is temperature an effect modifier of the association between green tea intake and gastric cancer risk?  European Journal of Cancer Prevention. January 2010; 19(1): 18-22

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