A surprising study by German scientists has revealed that adding milk to tea stops its ability to dilate blood vessels and give antioxidant benefits, two protective factors for a healthy heart and cardiovascular system.

The study is published online in the European Heart Journal and was conducted by a group of scientists from the University of Berlin's Charité Hospital.

The small research study was conducted on 16 healthy women volunteers who drank half a litre of black tea with and without skimmed milk, or just hot water as a control. Before and after drinking their tea or water, the women were examined by ultrasound to measure the dilation of an artery in their arm.

The results showed that the "flow mediated dilation" (FMD) of the artery was significantly improved by black tea, but this effect was completely "blunted" by the additon of milk.

The researchers then explored the impact of milk proteins on the aortas of rats. They found that black tea caused the rat aortas to relax and also stimulated the production of nitric oxide that makes this happen. However, with milk neither of these things happened, and they suggest that the caseins (types of milk protein) were combining with tea catechins (antioxidants that comprise about a quarter of the dry weight of tea) to prevent them from stimulating the nitric oxide production.

Previous studies have shown that tea protects against cardiovascular disease, but nobody had investigated the effect of adding milk to the drink. Scientists have been puzzled about the fact that the UK, a high tea-consuming nation, does not report the extent of health benefits of other tea drinking populations. This could be because most tea in the UK is drunk with milk, the researchers say.

The researchers are not suggesting that people who have milk in their tea suddenly switch to black tea, but they do recommend now and again that if you are used to having it with milk, then have it occasionally without milk because you could increase the benefit to your heart.

The UK drinks 165 million cups of tea a day, which is equivalent to an average of 3 cups per person. Tea is consumed on a regular basis by 70 per cent of the population.

"Addition of milk prevents vascular protective effects of tea."
Mario Lorenz, Nicoline Jochmann, Amélie von Krosigk, Peter Martus, Gert Baumann, Karl Stangl and Verena Stangl.
European Heart Journal, doi:10.1093/eurheartj/ehl442

Health benefits of tea (Wikipedia).

Written by: Catharine Paddock
Writer: Medical News Today