LapLap

Already well known is that people with Japanese ancestry are more likely to develop gastric cancer than other Brasilians. But you haven't addressed this at all. Have your GI specialist friends discussed this aspect with you?

I cannot drink large quantities of matcha. I find it is way too strong and only need a small quantity to feel a "buzz". Doesn't surprise me that people who would choose to drink copious quantities (far more than what would be considered normal either in Japan or elsewhere) would suffer unexpected consequences. Also, it would be interesting to know what passes for Matcha in Southern Brazil.
Green tea used to be the tea of choice when it was originally introduced in Europe. Unfortunately, it developed a reputation for becoming meddled with (copper filings and other impurities were often mixed in to increase profit margins) and black fermented tea took over as the number one choice. Sealed bags eventually brought total confidence in tea.

I can't help but be suspicious of what people who aren't from one of the world's richest countries are actually drinking when they are taking such vast amounts of a famously expensive commodity.