Steeping green tea leaves - how many times can I steep them, and do they lose flavanoids over steeps?
Nutrition itself is off-topic.  However, keep in mind the following:

There are many compounds in tea leaves and some dissolve early, and some a little later.  At some point (around 5-10 minutes of steeping at ~95&deg;C), you will lose majority of the 'good stuff' and continue picking up less desirable compounds.  

You will notice that while colour might persist, the taste will be come less and less desirable.  In some cultures re-using tea leaves is considered a faux-pas because of this.

If you find your tea to be too strong after steeping, the best thing is to reduce the amount of leaves for the next time; as opposed to steeping them multiple times.