Norwegian Mental Illness Heart Health Study

People with severe mental illness (SMI) such as schizophrenia spectrum- or bipolar disorder face a markedly increased risk of early death compared to the general population, with cardiovascular disease (CVD) as the leading cause. This excess risk is partly explained by modifiable lifestyle-related risk factors such as physical inactivity, poor diet quality, and the metabolic side effects of antipsychotic medication. Despite this, people with SMI often receive less preventive somatic care and limited support to adopt healthier habits.

The scientific evidence for the effectiveness of lifestyle interventions in this population is still limited, and previous trials have yielded mixed results. The most promising studies have combined professional dietary counselling with physical activity at moderate to high intensity. This study builds on previous research and clinical experience with the patient group, and responds to a documented need for targeted, feasible interventions in mental health services.

The study aims to contribute to the evidence base by testing a feasible, multidisciplinary intervention integrated in routine mental health care. This randomized controlled trial (RCT) will evaluate the impact of a structured lifestyle program on the estimated CVD risk and associated metabolic and lifestyle outcomes in Norwegian adults with an SMI.

Participants will be randomized in a 1:1 ratio to either a 6-month lifestyle intervention or a control group receiving treatment as usual (TAU) in mental health care. The study will include approximately 70 overweight adults with schizophrenia spectrum (ICD-10 F20-29) or bipolar disorder (ICD-10 F31). For ethical reasons, the control group will be offered the same lifestyle program after the 6-month trial period, without accompanying data collection.

The intervention period lasts six months and consists of:

* Monthly one-on-one sessions with a registered clinical dietitian, focused on cardioprotective dietary changes, practical food strategies, and weight reduction. * Monthly group-based physical activity sessions led by an instructor, tailored to the participants' physical capacity. * Support to follow a personalized training plan meeting the recommended amount of physical activity on moderate-high intensity.

The intervention is designed to integrate into existing mental health services and accommodate the needs and challenges specific to people with SMI, such as medication side effects, low energy levels, and cognitive symptoms. User panels including patients with lived experiences are involved in tailoring the intervention. Fidelity and feasibility will be evaluated through structured feedback and attendance records.

The study will assess whether adherence to a healthy lifestyle, measured with the DIGIKOST Lifestyle Index, affects estimated 10-year CVD risk, using a validated risk prediction tool. Weight monitoring, blood pressure recordings and blood test results are incorporated in the risk prediction, and this data will be assessed regularly throughout the study period. Secondary outcomes include changes in objectively measured physical activity (accelerometer), adherence to national lifestyle recommendations and diet quality (measured with a validated food frequency questionnaire, DIGIKOST), body composition (Bioelectrical impedance), waist circumference, body weight, and relevant biomarkers including blood lipids and glucose, in the intervention group compared to TAU. The presence of metabolic syndrome will also be evaluated using IDF and ATP III criteria. Health-related quality of life will be measured using a simple and validated questionnaire (PROMIS-29).

Statistical analysis will follow the intention-to-treat principle and use linear mixed-effects models to evaluate between-group changes from baseline to 6 months. In addition, interim measurements at 3 months will be used for secondary analyses to assess early changes, explore the trajectory of intervention effects, and monitor adherence and retention. This mid-intervention timepoint is also collected in the control group to enable temporal comparisons and better understand the dynamics of lifestyle change in both groups. Exploratory analyses will investigate predictors of adherence, effect heterogeneity, and timing of response.

The trial is part of a PhD project and will contribute to improved understanding of how lifestyle interventions can be tailored and implemented to improve physical health in people with SMI. The findings may help inform future clinical practice and reduce somatic health disparities in this underserved population.

• Change in Objectively Measured Physical Activity (Accelerometer) [Time frame: From baseline to 6 months]
• Change in lifestyle adherence score (DIGIKOST Lifestyle Index) [Time frame: Baseline and 6 months]
• Change in Diet Quality (DIGIKOST Diet Index and 24-Hour Dietary Recall) [Time frame: From baseline to 6 months]
• Presence and Change in Metabolic Syndrome (IDF and ATP-III Criteria) [Time frame: Baseline, 3 months and 6 months]
• Change in Blood Biomarkers Related to Cardiometabolic Health [Time frame: From baseline, at 3 months and after 6 months]
• Change in Body Weight [Time frame: Baseline, 3 months, and 6 months]
• Change in Waist Circumference [Time frame: Baseline, 3 months and 6 months]
• Change in Blood Pressure [Time frame: Baseline, 3 months, and 6 months]
• Change in Body Composition (BIA) [Time frame: Baseline, 3 months and 6 months]