Previous research has shown that drinking tea improves blood flow and the ability of arteries to relax.
Researchers from the Charite Hospital at the University of Berlin in Mitte found that adding milk to the tea eliminates the protective effect against cardiovascular disease, Health News reported.
Tea is second only to water in worldwide consumption so any benefits could have important public health implications. But until now it was not known whether adding milk had an impact.
The researchers discovered that proteins called caseins in milk decrease the amount of compounds in tea known as catechins, which increase its protection against heart disease. The researchers compared the healthy effects of drinking boiled water and tea with and without milk on 16 healthy women.
Using ultrasound, they measured the function of an artery in the forearm before and two hours after drinking tea.
It was found that black tea significantly improved blood flow as compared to drinking water but adding milk blunted the effect of the tea. Whereas drinking tea significantly increased the ability of the artery to relax and expand to accommodate increased blood flow as compared to drinking water, the addition of milk completely prevents the biological effect.
Tests on rats produced similar results. When rodents were exposed to black tea they produced more nitric oxide, which promotes dilation of blood vessels. But adding milk blocked the effect.
The findings could explain why in countries such as Britain, where tea is regularly consumed with milk, have not shown a decreased risk of heart disease and stroke from drinking tea.
Tea has also been shown to have a protective effect against cancer so the findings could have further implications.
Since milk appears to modify the biological activities of tea ingredients, it is likely that the anti-tumour effects of tea could be affected as well.
Source: The News, 2nd January 2009