Adding milk to a cup of tea can destroy its ability to protect against heart disease, according to research.
A small German study found drinking black tea significantly improved the ability of arteries to relax and expand to keep blood pressure healthy.
But the European Heart Journal paper also found proteins in milk, called caseins, blocked this effect.
It is estimated as many as 98% of UK tea-drinkers prefer milk in their favourite cuppa.
The researchers tested the effects of tea in 16 humans and on rat tissue.
They showed molecules in the tea called catechins helped dilate the blood vessels by producing a chemical called nitric oxide. The caseins in milk prevented this effect by reducing the concentration of catechins in the tea.
Senior researcher Dr Verena Stangl, professor of cardiology at the Charite Hospital, in Berlin, said: "Our results thus 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."
Source - BBC