"Keeping a diary is bad for your health, say UK psychologists. They found that regular diarists were more likely than non-diarists to suffer from headaches, sleeplessness, digestive problems and social awkwardness."
This was taken from a 2004 article at NewScientist.com
Well, that must apply to blogging too because I have all those symptoms. Although a strong argument could be made that people with those symptoms are more likely to be come diarists or bloggers. Certianly the social awkwardness thing. " But she acknowledges that her experiment could not demonstrate which came first - the diary writing or the health problems."
The article also says that those who have had traumatic experiences in their life and write about it were even more likely to have health problems. Again, an argument can be made that people who have had traumatic experiences in their life are going to have stress and health problems and be more likey to write about traumatic experiences (...because they actually happened). Though I'll admit it says nothing about what percentage of people who have had traumatic experiences feel compelled to write it down.