Research in this field has been proceeding since the mid 1980s, and a ponderous body of results are now available. These benefits are both physical and emotional. Evidence has been gathered in at least three threads: "soft" behavioral research, "hard" brain imaging research, and anecdotal evidence from therapists of various sorts as well as writers themselves.
This is a multi-faceted field of discovery. Some health benefits such as lowered blood pressure, increased immune and cardio-vascular function or relief of symptoms like asthma or arthritis pain are physical. Emotional health benefits like relief from depression or enhanced sense of satisfaction and happiness are emotional. Stress reduction bridges the physical and emotional realms.
A major body of behavioral research has been patterned after the original work of James Pennebaker, using spontaneous, unstructured freewriting, not intended for sharing with anyone but researchers. Another line of research addressed journaling. Much less research has been devoted to the more public forms of writing, but many inferences are easily drawn.
The results are clear: expressive writing is good for you, however you go about it. The challenge is finding a way to reap the maximum benefits within the bounds of your available time and interest. Posts on this blog explore how to select an appropriate expressive writing form and apply relevant writing techniques to get healthful results from writing you do for other reasons.