The protective effect that tea has on the cardiovascular system is totally wiped out by adding milk, according to European researchers. Their research, appearing in the European Heart Journal, showed that while black tea significantly improves the ability of the arteries to relax and expand, adding milk completely blunts the effect.
The results come from experiments involving healthy postmenopausal women who drank either freshly brewed black tea, black tea with 10 percent skimmed milk, or boiled water (as a control). The researchers measured the endothelial function of the brachial artery in the forearm by high resolution ultrasound before and two hours after drinking.
"We found that, whereas drinking tea significantly increased the ability of the artery to relax and expand to accommodate increased blood flow compared with drinking water, the addition of milk completely prevents the biological effect," said study author, Dr Mario Lorenz.
The results provide a possible explanation for the lack of beneficial effects of tea on the risk of heart disease in the UK, a country where milk is usually added. Interestingly, the findings could also have implications for cancer, against which tea has also been shown to be protective. "Since milk appears to modify the biological activities of tea ingredients, it is likely that the anti-tumor effects of tea could be affected as well. I think it is essential that we re-examine the association between tea consumption and cancer protection, to see if that is the case," said co-researcher, Dr Verena Stangl.
The researchers explained that the culprit in milk is a group of proteins called caseins, which they found interacted with the concentration of catechins in the tea. Catechins are the main contributor to tea's protective effect against cardiovascular disease. The team is now in the process of comparing the effects of green and black tea on vascular function. "It's an ongoing question whether green tea, with its higher catechin content, is superior to black tea in regard to endothelial function," concluded Dr Stangl.
Source: European Society of Cardiology