WASHINGTON – In many parts of the world, it’s customary to add milk to tea.

But that addition could reduce many of the health benefits associated with drinking tea, the most consumed beverage in the world next to water.

A new study published in The European Heart Journal found that adding milk may strip tea of antioxidants and vitamins. It could also reduce its ability to promote a strong immune system and reduce cell damage. Cavity prevention and improved blood sugar levels could also suffer by adding dairy.

The New York Times reports that even a small amount of skim milk can blunt the effects of tea.

Researchers tested both people and mice. The 16 humans drank black tea, black tea with milk or boiled water. Those who consumed black tea experienced improved arterial function, but those effects diminished when milk was added.

In mice, milk counteracted the favorable health effects of the drink on cardiovascular function.

It wasn’t just an issue with dairy, either. Proteins in soy milk also had the same effect as regular milk.

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