Background & aims: A potential downside of colorectal cancer screening is that a "health certificate effect" might have negative effects on lifestyle. The aim of the present randomized controlled trial was to evaluate lifestyle changes in a group of individuals offered flexible sigmoidoscopy screening compared with a control group and also in relation to screening outcome.
Methods: Men and women aged 50-55 years were drawn by randomization from the population registry to be invited for flexible sigmoidoscopy screening (n = 6961) or not to be invited (n = 7000). Both groups were asked to fill in a questionnaire on selected lifestyle indicators at baseline and 3 years later. From both rounds, 3598 pairs of completed questionnaires were available for analysis from the screening group and 3462 from the control group.
Results: Both groups revealed a desirable change in most lifestyle indicators. A weight gain in the screening group was, on average, 0.24 kg higher than in the control group (P = .023). The screening group had poorer improvement in score for smoking (mean difference, 0.05; P = .013) and exercise habits (mean difference, -0.12; P = .001) and a lower increase in servings/day of fruit, berries, and vegetables (mean difference, -0.10; P = .001) compared with controls. The weight gain in screen-negative individuals (ie, no neoplasia) was, on average, 0.5 kg (P = .020) more than for screen positives.
Conclusions: The present study has demonstrated a possible health certificate effect of flexible sigmoidoscopy screening and screening outcome on lifestyle. Although modest, these findings indicate a potential need for patient education in screening programs.