According to recent research at the Charité Universitätsmedizin Berlin—the university hospital for Free University and Humboldt University, both of Berlin—the largely British custom of adding milk to black tea might negatively impact the cardioprotective vascular effects of the tea. The results of this research were recently published online by the European Heart Journal (see http://eurheartj.oxfordjournals.org/cgi/content/abstract/ehl442v1).
The researchers studied the vascular effects of tea, with or without milk, in 16 healthy female volunteers. Each consumed either 500 mL of freshly brewed black tea, black tea with 10% skimmed milk, or boiled water (control). They then studied the vascular impact in the subjects.
They found, as previous studies have shown, that black tea significantly improved vascular flow compared to water. However, the researchers noted, tests showed that adding milk “completely blunted the effects of tea.”
In order to support these findings, the team performed similar experiments on isolated rat aortic rings and endothelial cells. As was shown in human subjects, the tea had a positive impact on vascular function, while “all effects were completely inhibited by the addition of milk to tea.” The researchers hypothesized that the caseins in the milk “accounted for these inhibiting effects of milk, probably by formation of complexes with tea catechins.” They note that these results warrant further research into the physiological interaction of milk and tea, as well as on the behavior of nutritional flavonoids in general.
The researchers concede that other studies have yielded contradicting results. Also, the Milk Development Council, Cirencester, England—an farmer- and government-funded organization supporting the dairy industry in the United Kingdom—also called attention to the small sample size used for the study.
The Berlin research team is also currently involved in comparing the vascular effects of green and black; green tea is almost always consumed without milk.