Perich, T., et al. (2013). The association between meditation practice and treatment outcome in Mindfulness-based Cognitive Therapy for bipolar disorder. Behaviour Research and Therapy, 51 (7), 338–343.
From the Abstract: This study aimed to examine the impact of quantity of mindfulness meditation practice on the outcome of psychiatric symptoms following Mindfulness-based Cognitive Therapy (MBCT) for those diagnosed with bipolar disorder. Meditation homework was collected at the beginning of each session for the MBCT program to assess quantity of meditation practice.
… A greater number of days meditated during the 8-week MBCT program was related to lower depression scores at 12-month follow-up, and there was evidence to suggest that mindfulness meditation practice was associated with improvements in depression and anxiety symptoms if a certain minimum amount (3 times a week or more) was practiced weekly throughout the 8-week MBCT program.