It is well-known that tea is rich in antioxidants (substances that protect cells from the damage caused by unstable molecules known as free radicals). Because it is common in the UK to add milk to tea a recent study published in Nutrition Research analysed how the addition of whole, semi-skimmed and skimmed milk changes the antioxidant content of five brands of tea. All brands were found to be a good source of antioxidants but when the milk was added, the availability of antioxidants decreased. This effect was observed for all three sorts of milk and was strongest for the skimmed milk.
Ryan, Petit, 2010. Addition of whole, semi-skimmed, and skimmed bovine milk reduces the total antioxidant capacity of black tea. Nutrition Research. 30 (1) 14-20.