The study examines the efficacy of a stepped care approach for depressed diabetes patients (first study objective). 256 patients with diabetes and comorbid subthreshold or clinical depression will be randomly assigned to either a stepped care approach or a treatment-as-usual condition. The stepped care approach consists of three treatment steps comprising diabetes-specific cognitive-behavioral therapy (CBT) (group), depression-specific CBT (single), and psychotherapeutic and/or psychiatric treatment (single). Patients assigned to the stepped care approach will be treated stepwise until a clinically significant reduction of depressive symptoms is attained or all three treatment steps are passed.

The primary outcome of the first study objective is a clinically significant reduction of depressive symptoms in the 12-month follow-up. Secondary outcomes are reduction of diabetes-related distress and improvement of well-being, health-related quality of life, diabetes acceptance, diabetes self-care, and glycaemic control. Additionally, cost-benefit analyses will be performed.

The second study objective is to analyse associations between diabetes, depression, and the serum levels of inflammatory markers.

The third study objective is to analyse the courses of depressive conditions in diabetes with regard to recovery rates and incidence of major depression.

Compared to persons without diabetes, rates of depressive disorders and mood are doubled in diabetes patients. Epidemiologic studies have shown point prevalence rates of 10 - 14% for major depressive disorder and an additional proportion of almost 20% with subthreshold depression (defined as elevated depressive symptoms without meeting criteria for a specified clinical disorder). Depression and subthreshold depression in diabetes are associated with reduced quality of life, increased diabetes-related distress, and elevated health care costs. Furthermore, depression as well as subthreshold depression seem to be major barriers to an effective self-management of the disease and have been associated with reduced glycaemic control and hyperglycaemia. Both conditions seem to be independent prognostic factors for subsequent morbidity and mortality in diabetes.

Depressive conditions are commonly treated with psychotherapeutic or pharmacologic antidepressive therapies. Since the majority of diabetes patients is suffering from subthreshold depression, evaluated and suitable specific intervention concepts are rare. Moreover, the large variation of symptom levels of depressive patient groups suggests that different types of treatment with different treatment intensities may be required to match individual demands. The issue of 'optimal' treatment also regards concerns about overtreatment and undertreatment of particular patient groups with depressive conditions. Thus, an successive order of treatment steps of increasing intensity appears useful. Since depression in diabetes often is associated with high diabetes-related problems and distress, diabetes-specific as well as depression-specific interventions may be required.

We developed a stepped care approach with three treatment steps comprising diabetes-specific CBT (group), depression-specific CBT (single), and psychotherapeutic and/or psychiatric treatment (single).

The study is a randomized efficacy trial in which the efficacy of the stepped care approach is compared to a treatment-as-usual condition (standard diabetes education). 256 patients with diabetes and comorbid subthreshold or clinical depression will be randomly assigned to either the stepped care approach or the treatment-as-usual condition. Patients assigned to the stepped care approach will be treated stepwise until a clinically significant reduction of depressive symptoms is attained or all three treatment steps are passed.

The primary outcome is a clinically significant reduction of depressive symptoms in the 12-month follow-up. Secondary outcomes are reduction of diabetes-related distress and improvement of well-being, health-related quality of life, diabetes acceptance, diabetes self-care, and glycaemic control. The decisive measurement of this outcomes are conducted 12 months after the treatment (12 month follow up). Additionally, cost-benefit analyses will be performed.

Besides testing the efficacy of the stepped care approach (first objective), there are two additional study objectives:

The second study objective is to analyse associations between diabetes, depression, and the serum levels of inflammatory markers (C-reactive protein (CRP), Interleukin (IL)-6, IL-18, IL-1Ra, Adiponectin, Monocyte chemoattractant protein (MCP)-1). Additionally, the impact of depression treatment on the levels of these markers will be examined.

The third study objective is to analyse the courses of depressive conditions in diabetes with regard to recovery rates and incidence of major depression in subclinically or clinically depressed diabetes patients treated as usual vs. given an intervention.

Inclusion Criteria:

• Age >=18 and <=70
• Diabetes mellitus
• Elevated depressive symptoms (CES-D score >=16) and/or elevated diabetes-related distress (PAID score >=40)
• Sufficient language skills (German)
• Written informed consent

Exclusion Criteria:

• Severe depressive episode (F32.2/ F32.3)
• Current psychotherapeutic/ psychiatric treatment
• Current antidepressive medication
• Suicidal intention
• Current schizophrenia/ psychotic disorder, specified eating disorder, bipolar disorder, addictive disorder, personality disorder
• Severe physical illness (i.e. cancer, multiple sclerosis, dementia)
• Terminal illness
• Bedriddenness
• Guardianship