> I drink black tea rest of the day

Black tea contains a considerable amount of caffeine too. Aside from that, I know of two people whose years-long mysterious health effects disappeared (one with stomach troubles and the other with bad muscle cramps) after stopping their all-day >1L black tea consumption. The tannins in tea bind to iron, so it might cause iron deficiency anemia (although studies yield conflicting results), which especially woman are already predisposed to, and for which iron deficiency tests are often calibrated towards men .

Let me clarify some of the points you have rightfully brought up.

As a disclosure, I hail from Turkey. We consume most tea per capita by a large margin, so we might have adapted to this. I don't know. I'm drinking tea regularly since I'm six, and my family is drinking considerable amount every day, too.

Let's start with iron deficiency which is the most widely touted side-effect. Regardless of the amount of the tea, I have never had iron deficiency or low-iron case in my life. On the contrary, I'm a type of person who wears t-shirt all year long, and generally pretty warm all-over. I mean, the room has AC on, and I also add a small desk fan to keep my cool right now. I'm not overweight either. Nobody from my immediate or larger family has low-iron case either (regardless of gender), and we all drink lots of tea, all day long. So there might be some genetics here.

Mayo clinic suggests that tea has "half the caffeine" of tea (I brew both) [0], however their effects on my body is wildly different. If I overshoot my daily coffee consumption, my heart rate increases and I feel the usual "tension" from high caffeine consumption. However, drinking ~2L of brewed tea doesn't do anything to me. Does not affect my sleep, anxiety levels or anything. It helps me concentrate, sure, but without all the bad side effects of coffee over-consumption. There's a paper about it, but it's sponsored by Unilever IIRC, so I won't share that.

Badly brewed, overly dark or stale black tea brews are not kind to the stomach. That's true. There's a kind of finesse to do it properly. From dosage to waiting times. Even if you do everything right, some people's body doesn't like tea, and that's alright.

Cramps? Now I'm hearing it for the first time, but I don't discount or dismiss it. It's just I never heard it from anyone around.

So while these effects might be true, these are not universal. I was sipping tea by 11PM yesterday and I was dead asleep at midnight, for example. If I have drank another half mug of coffee, I'd be watching sunrise probably.

Addenda: Human body can silently signal what it wants and what it doesn't. Sometimes I automatically stop drinking tea/coffee and switch to water for example. Listening to the body is essential to preserve its balance. Forcing it never ends well. Body is wiser than the mind.

[0]: https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-h...