Drinking tea significantly improves blood flow and the ability of the arteries to relax, but the addition of milk blocked this biological effect.  The culprit is believed to be casein, one of the primary proteins in cow’s milk.  The study did not address the addition of milk alternatives that do not contain these proteins, such as rice milk. 

Researchers are now concerned that milk may also block the anti-tumor effects of tea.  Further studies on the relationship of milk, tea, and cancer may be on the horizon.  For the full story from Reuter’s, read “Milk cancels health benefit of drinking tea: study.”  For the actual published study, check out the review from the European Journal of Clinical Nutrition, “Black tea – helpful or harmful?”