Vitamin C Gives Staying Power to Antioxidants

Those who take lemon juice in their tea may be getting far more of the health benefits.
Catechins are naturally occurring antioxidants found in tea; complementing green tea with either citrus juices or vitamin C increases the amount of catechins available for the body to absorb.

Catechins may be responsible for some of green tea's reported health benefits, such as a reduced risk of cancer, heart attack and stroke. But catechins are relatively unstable in the intestines meaning that less than 20 percent of the total generally remains after digestion.

Citrus juice increased available catechin levels by more than five times, and vitamin C increased recovered levels of the two most abundant catechins by six-fold and thirteen-fold.
Lemon juice caused 80 percent of tea's catechins to remain available.

Sources:
Science Blog November 13, 2007