On Tea

In the excerpt from Empire of Tea, there is a list of all the health benefits thought of tea at the time it was beginning to catch on.  This may be missing the point of the whole article, but that list was something that really puzzled me.  How did they know those health benefits?  There can't have been that much study on tea itself, as it was relatively new, and they hadn't the means of technology to study such health benefits over such a period of time.  Also, nothing can possibly effect that many parts of the body, and blood can't really be purified in such a way.  But, I feel like it would have been immoral to make up such things just to sell something.  Gasp!