Objectives: In a trial completed in 2010, US patients with diabetes and depression were randomized to usual care or telephone cognitive behavioural therapy that emphasized physical activity. Twelve-month intervention effects were observed for blood pressure, depression, and pedometer-measured step-counts. This study examined variation in intervention effects across patient subgroups defined by a measure of clinical complexity.
Methods: Three groups of patients were identified at baseline using the Vector Model of Complexity that recognizes socioeconomic, biological, behavioural, and other determinants of treatment response. Complexity-by-intervention interactions were examined using regression models.
Results: Intervention effects for blood pressure, depression, and step-counts differed across complexity levels (each p < 0.01). Effects on Beck Depression Inventory scores were greater in the low-complexity group (-8.8) than in the medium- (-3.2) or high-complexity groups (-2.7). Physical activity effects also were greatest in the low-complexity group (increase of 1498 steps per day). In contrast, systolic blood pressure effects were greater among intervention patients with high complexity (-8.5 mmHg).
Conclusions: This intervention had varying impacts on physical and mental health depending on patients' clinical complexity. Physical activity and depressive symptom gains may be more likely among less complex patients, although more complex patients may achieve cardiovascular benefits through decreased blood pressures.
Trial registration: ClinicalTrials.gov NCT01106885.