Researchers from Carnegie Mellon University in Pittsburg, US, asked 73 students to write a short essay on subjects such as the importance of friends and family.
A group of students rated their levels of stress over last month, and half the group then performed the self-affirmation exercise.
While the stressed-out students had been found to have performed nearly 50 percent worse on a problem-solving test, after writing the essay their scores caught up.
David Creswell, assistant Professor in psychology at the university said: "A brief self-affirmation activity is sufficient to buffer the negative effects of chronic stress on task performance and can improve the ability to solve problems in a flexible manner during high stress periods."
"Our study suggests that self-affirmation may increase creativity and insight in stressed individuals."
Earlier studies had shown how self-affirmation exercises could reduce acute stress. But the link between these improvements and chronic stress-related effects was unknown.