Testing the effects of an expectancy-based intervention among adolescents: Can placebos be used to enhance physical health?

Abstract

It has been suggested that the well-known health benefits associated with exercise can be explained by a placebo effect, and that greater effort should be given to convince people that their current behaviors have desirable health consequences. The overall purpose of this study was to test the efficacy of this “mind-set matters” hypothesis through the use of an expectancy-based intervention with adolescents. The study involved a four week randomized controlled trial with 348 Grade 9 adolescents (M _age = 14.07 yrs, SD = 0.30), from four high schools, taking part in either a placebo-intervention condition (n = 188) or a control condition (n = 160). Participants in the placebo-intervention condition were informed that what they are already doing in school physical education lessons fulfills current recommendations for an active lifestyle. Participants in the control condition were not given this information. Four weeks after the intervention, adolescents in the placebo-intervention condition did not demonstrate significant changes in physiological health-related measures (diet, weight, body mass index, percentage body fat, heart rate, mean arterial pressure). The findings question the external validity of the “mind-set matters” hypothesis with adolescents, and suggest that simply encouraging adolescents to believe that they are healthy may not enable them to respond with improved indicators of physical health.

Keywords:

• physical activity
• placebo
• intervention

Acknowledgements

This research was supported by the Canadian Foundation for Innovation and the Peter Wall Institute for Advanced Studies. Mark Beauchamp was supported by a career investigator award from the Michael Smith Foundation for Health Research (MSFHR). Ryan Rhodes and William Sheel were supported by New Investigator Awards from the Canadian Institutes of Health Research. Megan Sherman was supported by graduate scholarships from Natural Sciences and Engineering Research Council of Canada and MSFHR. William Dunlop was supported by graduate scholarships from the Social Sciences and Humanities Research Council of Canada and MSFHR.