by john.b » Feb 22nd, '17, 23:46
Health benefits are a controversial subject related to tea. A lot of people that are really into tea just dismiss it as unresolvable because the claims are almost always based on hearsay (background like Chinese folk wisdom), and researched support of that is limited, with some research seeming biased (supported by tea producers). Of course some of the claimed health benefits could still be real; lack of proof and evidence isn't negative evidence on it's own. The background for research on both benefits and risks includes the normal problems with limited range studies. For example, correlation doesn't equal causation, so lots of real trends related to parallels in tea intake and benefits / health problems could be caused by other factors that pair with trends among people that drink more tea.
Health risks are also problematic to define. The consensus is that moderate tea input poses essentially no risk. Discussion of the potential for some tea being contaminated by pesticides or containing traces of chemicals from fertilizers comes up but again it's hard to assess real risks, and it seems like those are no higher than for those from foods if tea is consumed in moderation. It's hard to know what types of organic sourcing offsets risks, given the risks themselves are hard to define, and organic claims may be based on varying validity.
Caffeine input--perhaps the main risk--is only a concern for higher than average consumption, so probably not a factor for most when consuming even a half dozen cups of tea a day. At a rough estimate teas are said to contain 30 to 40 mg. of caffeine per cup (although that does vary quite a bit) and the normal daily limit is 400 mg. (although that varies quite a bit too; people have different sensitivity to caffeine), so 8 cups of tea is probably still fine, for most people, if that's the only caffeine input. For many it doesn't work well to consume much of that in the evenings for the obvious reason.
It doesn't come up much in discussion compared to those factors but in my opinion tea shouldn't be used as a complete replacement for drinking water. All that is a long story too, about whether or not tea (caffeine) really is a diuretic, if it causes people to expel more fluids. It probably varies by individual more than anything, but some evidence suggests the level of effect varies by how much tea is consumed, so for 3 to 4 cups worth maybe not (150 mg. caffeine dosage range), but for 8 or more cups per day maybe much more so. Based on personal experience mixing in some water consumption with drinking tea resolves that.