A Telephone-Delivered Physical Activity and Dietary Intervention for Type 2 Diabetes and Hypertension: Does Intervention Dose Influence Outcomes?

PURPOSE: To examine associations of intervention dose with behavior change outcomes in a telephone counseling intervention for physical activity and dietary change. DESIGN: Secondary analysis of intervention participants from a cluster-randomized controlled trial. SETTING: Primary care practices in a disadvantaged community in Queensland, Australia. SUBJECTS: Adult patients with type 2 diabetes or hypertension. INTERVENTION: Patients (n = 228) received telephone counseling over a 12-month period. The initiation phase (1-4 months) consisted of up to 10 weekly or fortnightly calls; the maintenance-enhancement phase (5-12 months) consisted of up to eight monthly calls. MEASURES: Intervention dose was defined as the number of calls completed in total and during each phase and was categorized into tertiles. Diet and physical activity were measured using validated self-report instruments. ANALYSIS: Multivariate analyses of call completion and change in health behaviors. RESULTS: Those completing a high number of calls were more likely to be female, white, older than 60 years, retired, and earning less than an average weekly Australian wage. Relative to low call completion, high completion during the maintenance-enhancement phase was associated with significantly greater (least squares mean [SE]) behavioral improvement for the following: total fat intake as percentage of calories (-3.58% [.74%]), saturated fat intake (-2.51% [.51%]), fiber intake (4.23 [1.20] g), and moderate-to-vigorous physical activity (187.82 [44.78] minutes). CONCLUSION: Interventions of longer duration may be required to influence complex behaviors such as physical activity and fat and fiber intake.