The subject of caffeine in tea is an interesting one. Unfortunately, there is a lot of misinformation surrounding both (a) how much caffeine is in tea, and (b) the effect caffeine has on your body. I have written at length about the caffeine content of various teas, so this post explores the second question.
Public perception of caffeine:
There seems to be a widespread public perception that caffeine is "bad". One way you can tell that this is the case is that a number of tea companies market their teas as being "low in caffeine", whereas teas higher in caffeine are usually not labelled as such, and instead labelled with euphemisms or indirect statements such as "energizing" or "good for starting the day". People want to feel energized, but they don't want to consume much caffeine.
The success of decaffeinated tea, which is often highly inferior in taste to tea in its natural, caffeinated form, is also a testimony to this negative public perception. Some companies even sell decaffeinated green tea extracts, so that people can obtain the "health benefits" of the tea without the caffeine.
In this post I will argue that this attitude towards caffeine is irrational...it's a result of people taking an absolute "good / bad" view of a substance, rather than looking at a key concept: moderation.
People drink tea because of caffeine:
Granted, there are many reasons that people drink tea, inculding flavor, tradition, and expectations of certain health benefits. However, I do believe that, regardless of how many other factors come into play, caffeine is one of the primary reasons people drink tea, if not the primary reason. Tea does contain many other biologically active compounds, such as L-theanine; theanine in particular is known to interact with tea, so the topic becomes a bit complex, but the point is: tea contains caffeine, and people want to consume caffeine.
The evolution of caffeine:
Caffeine is an interesting chemical because it evolved in plants primarily as a biological defense. Caffeine is a poison, probably intended primarily to protect a plant against insects. This is why the caffeine tends to be concentrated in the tender new leaves, which are most in need of protection against being eaten.
Moderation is key:
The activity of caffeine in humans is in some sense a biological accident. A high enough dose of caffeine would kill a human, but a small dose provides a stimulating effect to the body and mind. Many chemicals are like this...nearly all drugs have a lethal dose and a therapeutic dose, and somewhere in between these there are middle doses where unpleasant side effects start to appear.
For caffeine, small quantities can provide a boost in alertness, improved concentration, and improved energy level. But higher amounts, or caffeine consumed at the wrong time, can cause a variety of unpleasant symptoms, both immediate and long-term, including jitters, feelings of malaise, weak and rapid heartbeat, anxiety, and insomnia. Some people are more sensitive to caffeine, either because of their own biology, or because of medications they are taking. But for the most part, the best way to approach caffeine is moderation. So, next time you hear or read someone explicitly or implicitly stating that caffeine is bad, respond by encouraging them to think about moderation rather than in strict good / bad terms.