Indeed, but you would really need to drink a lot of green tea to get the same amount of L-theanine you would in a supplement: "2.5 litres of brewed green tea would be needed to get 200mg of L-theanine". Also a question of how much dose you want of course...
Will we discover one day that we shouldnt have consumed the equivalent of jugs of green tea in a pill? I'm having trouble braining the internet saying short term L Theanine consumption "generally recognized as safe" but green tea (with all its chemicals) and supplements have been harmful.
This is a good and fair question (although noting that the doses in the second study seem extremely large compared to supplement values). I think the solution is to test, test, and test on as many things as possible which is not being done at the moment. Most supplements will probably not have any notable effect, like L-theanine in my case, so a precautionary principle would lead one to discontinue use.
High doses of green tea extract is not the same as isolated L-theanine. You'd have to show research on the latter here.
The writing in that first paper is so poor that it's hard to take it too seriously, but it's a narrative review, not a study. The second link is a study on a few rats.
Another study: "According to Kaneko et al., the content of l-theanine in matcha tea infusions amounts to 6.1 mg/L [50], while Unno et al. [9] found as much as 44.65 mg/g of that compound in matcha tea samples." Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7796401/
I'm not sure, but I guess one would use around 4 grams of matcha in a cup? So then at the upper bound you would come close to 200mg. But matcha has a lot of caffeine so probably not suitable to improve sleep.
