My parents were right...about tea, that is. I just read this:

"People who drank 5 cups a day of black tea for 2 weeks had 10 times more virus-fighting interferon in their blood than others who drank a placebo hot drink, in a Harvard study. The amino acid that's responsible for this immune boost, L-theanine, is abundant in both black and green tea--decaf versions have it, too. "

I'm afraid 5 cups a day would give you some pretty nasty looking teeth, though!!