Writing therapy has been found to improve people's physical and mental health. A review of studies into its effectiveness has found that, although the benefits are modest in absolute terms they are still very impressive in terms of the short amount of time that writing therapy takes compared to other interventions. In the vast majority of research participants write for 15-20 minutes but this is a matter of convention rather than being based on any evidence and no studies have sought to identify the minimum dosage required to reap the benefits of writing. A U.S. study of 49 students looked into the benefits of a very short (2 minutes x 2 days) writing intervention in which participants were asked to write about something they had found traumatic, or a positive experience or a neutral subject. 4-6 weeks later the students who had written about a trauma or a positive experience reported fewer health complaints than those who had written about a neutral topic.
Burton, Chad M. and King, Laura A. - Effects of (very) brief writing on health: the two-minute miracle. British Journal of Health Psychology March 2008, 13(1), 9-14