It would be unfair of me to only highlight the negative side effects of caffeine consumption. Obviously, moderation is probably advised for most people to prevent negative side effects, but I want to point out that studies have proven that there are positive side effects to drinking tea or coffee. I like the latter only occasionally when I go out, but I preferably drink tea. I used to drink caffeinated tea throughout the day in Canada when I was writing my cookbooks, but now that I live in the tropics in the mountains, tea loses its appeal past morning and only at night when it is cooler will I indulge in my Rooibos (decaf) tea or hot chocolate.
Although the article I will direct people to speaks about substantial (8 cups) of tea and coffee consumption (a bit crazy really for most of us), one has to realize that perhaps tea and coffee are not all bad. That said, I sometimes would call coffee, "beetle juice"! "Why?", someone may ask? Well, because my husband would get low blood sugar an hour or two after strong coffee and act like a Jekyll and Hyde around me (the bad one!). He can have mild coffee usually, but he seems to have more stable blood sugar when he drinks tea. Perhaps coffee and tea can raise blood pressure temporarily? This is another point brought up by someone who commented below the article. Everyone will decide, in any case, what is best for them. I just think it is interesting that for every subject on the internet, there seems to be at least two opposing views of thought, and one really has to use one's own head and experience to figure our what is the best advice to follow. I do enjoy the internet as it really does help in the long run for a person to do the research and become more pro-active in one's own health affairs.
Here is a great article that talks about the benefits of tea and coffee drinking and how it might help prevent strokes and cardiovascular disease: Dr. Briffa's article