THE EFFECTIVENESS OF ADHERENCE INTERVENTION IN A COLON CANCER PREVENTION FIELD TRIAL

Background. Adherence interventions were implemented in a 1-year community-based colon cancer prevention clinical trial (n = 110) using wheat bran fiber and calcium dietary supplements. The adherence promotion strategy was guided by a theoretical model. Methods. The adherence intervention contains both a generalized portion given to all participants and an individualized portion given to marginal (50-74% intake) and low (under 50% intake) adherers. A regression model was employed to assess the effectiveness of the interventions both at the first intervention and at subsequent times. Results. The Health Behavior in Cancer Prevention Model-based adherence promotion intervention was associated with retention of participants, both during the run-in period and after randomization (P = 0.05); and maximization of the percentage of the 13.5-g recommended fiber supplement consumed during the trial (92.5%). The positive effects of the adherence intervention were greater with first-time nonadherers and the control group than with the experimental group. The high-fiber group had notably more biological GI effects from the increased fiber intake, more preexisting comorbidities, and lower perceived cognitive and physical health status. Conclusions. Randomized participants had excellent adherence overall. Retention rates in the trial were better than would be expected without the adherence intervention, especially among those participants who may have been at higher risk for dropping out of the study. This suggests that a systematic, theoretically based adherence strategy should be further tested in clinical trial settings in which lower adherence is a problem. © 1992.