The purpose of this study is to determine whether mindfulness-based cognitive therapy (MBCT)and cognitive behavioral therapy (CBT)are effective in reducing depressive symptoms in patients with diabetes.

Depression is a common co-morbidity of diabetes, negatively affecting physical performance, glycemic control, adherence to medication, and dietary, and exercise recommendations. Modalities of psychotherapy like cognitive behavioral therapy (CBT) and mindfulness-based cognitive therapy (MBCT) can reduce depressive symptoms in patients with medical conditions. However, proper designed randomized trials assessing and comparing effectiveness of these psychological interventions are rare.

This longitudinal study aims to investigate the effectiveness of CBT and MBCT in reducing depressive symptoms in diabetes patients. Furthermore, potential moderators and mediators of treatment effect will be explored, as well as the role of common factors and treatment integrity.

Inclusion Criteria:

• Diabetes mellitus Type 1 or 2 for at least three months prior to inclusion
• Written informed consent
• Age ≥ 18 and ≤ 70
• Depressive symptoms as assessed by BDI-II score ≥ 14 (cut-off score indicating the presence of at least mild symptoms of depression)

Exclusion Criteria:

• Not being able to read and write Dutch
• Severe (psychiatric) co-morbidity
• Acute suicidal ideations or behavior
• Pregnancy
• Receiving an alternative psychological treatment during or less than two months prior to starting the participation in the study

Using an antidepressant drug during participation in the present study is allowed, on condition that a patient has been on stable medication regimen for at least two months prior to inclusion in the study, and that no new treatment with an antidepressant is initiated during the course of the study