Green tea this, and green tea that, but black still accounts for 90 percent of tea sold in Western countries. Is it doing anything for us?
PROBLEM: Green tea has a lot of simple flavonoids called catechins. They're what's most implicated when we read about green tea improving/preventing diseases. When tea oxidizes and becomes black, the types of flavonoids change. There are fewer simple catechins and more complex theaflavins and thearubigins. (Real words, I promise. I think the people who came up with them read a lot of Tolkien.) These complex flavonoids haven't been studied as much.
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METHODOLOGY: Researchers in Geneva, London, and Paris compared black tea consumption with data from the World Health Survey on respiratory and infectious diseases, cancer, cardiovascular disease, and type 2 diabetes in 50 countries.
RESULTS: "The black tea vector was negatively correlated with the diabetes vector -- and was not correlated with any of the other four health indicators."
CONCLUSION: Places where people drink more black tea have significantly lower rates of type 2 diabetes.
Is it because of the black tea? Given the biochemical effects of flavonoids on the pancreas suggested by previous research (protecting/regenerating pancreatic beta cells, which can be depleted in type 2 diabetes), it could be. Other research hasn't found flavonoids to be protective against insulin resistance, though. So, we need more info.