Caffeine reduces the risk of women with diabetes dying prematurely by 51% for those who drank 100mg caffeine / day (1-3 cups tea per 2dl depending on the type of tea) and 66% for those who drank 200mg caffeine / day
In the case of men, caffeine did not have the same effect
https://www.dagensmedicin.se/artiklar/2017/09/14/kaffe-kan-fa-diabetessjuka-att-leva-langre/
http://www.abstractsonline.com/pp8/#!/4294/presentation/5356
If there is caffeine you are looking for when drinking your tea then matcha is your best choice. There you get most caffeine as you drink the whole leaf (on picture, matcha midori)