One of the more powerful compounds in green tea is the antioxidant Epigallocatechin Gallate (EGCG), which has been studied to treat various diseases and may be one of the main reasons green tea has such powerful medicinal properties.
Green tea also has small amounts of minerals that are important for health.
Try to choose a higher quality brand of green tea, because some of the lower quality brands can contain excessive levels of fluoride (2).
That being said, even if you choose a lower quality brand, the benefits still far outweigh any risk.