Haworth et al., 2016: Performing acts of kindness and writing gratitude letters improved well-being and decreased depression and anxiety among twin pairs over ten weeks
Twin pairs were asked to complete two activities per week for 6 weeks. On the first three weeks, the activities were neutral controls (e.g., describe a room in their house). On weeks 4-7, they involved performing acts of kindness and writing gratitude letters. Well-being improved and symptoms of anxiety and depression declined over the treatment weeks, and this pattern continued at week 10.