Exercise and the Placebo Effect

In a study testing whether the relationship between exercise and health is moderated by one’s mindset, 84 female room attendants working in seven different hotels were measured on physiological health variables affected by exercise. Those in the informed condition were told that the work they do (cleaning hotel rooms) is good exercise and satisfies the Surgeon General’s recommendations for an active lifestyle. Examples of how their work was exercise were provided. Subjects in the control group were not given this information. Although actual behavior did not change, 4 weeks after the intervention, the informed group perceived themselves to be getting significantly more exercise than before. As a result, compared with the control group, they showed a decrease in weight, blood pressure, body fat, waist-to-hip ratio, and body mass index. These results support the hypothesis that exercise affects health in part or in whole via the placebo effect. The placebo effect is any effect that is not attributed to an actual pharmaceutical drug or remedy, but rather is attributed to the individual’s mind-set (mindless beliefs and expectations). The therapeutic benefit of the placebo effect is so widely accepted that accounting for it has become a standard in clinical drug trials to distinguish pharmaceutical effects from the placebo effect and the placebo effect from other possible confounding factors, including spontaneous remission and the natural history of the condition (Benson & McCallie, 1979; Brody, 1980; Nesbitt Shanor, 1999; Spiro, 1986). Kirsh and Sapirstein (1998), in a meta-analysis of 2,318 clinical drug trials for antidepressant medication, found that a quarter (25.16%) of the patients’ responses were due to the actual drug effect, another quarter (23.87%) were due to the natural history of depression, and half (50.97%) were due to the placebo effect. The placebo effect extends much further than medications or therapy: Subjects exposed to fake poison ivy developed real rashes (Blakeslee, 1998), people imbibing placebo caffeine experienced increased motor performance and heart rate (and other effects congruent with the subjects’ beliefs and not with the pharmacological effects of caffeine; Kirsch & Sapirstein, 1998), and patients given anesthesia and a fake knee operation experienced reduced pain and swelling in their ‘‘healed’’ tendons and ligaments (Blakeslee, 1998). More generally, studies suggest that 60 to 90% of drugs and other therapies prescribed by physicians depend on the placebo effect for their effectiveness (Benson & Freedman, 1996; Nesbitt Shanor, 1999). The placebo effect does not have to involve inert pills or sham procedures. Symbols, beliefs, and expectations can elicit powerful physiological occurrences, both positive and negative (Hahn & Kleinman, 1983; Roberts, Kewman, & Mercie, 1993). For example, the mere presence of a doctor increases patients’ blood pressure (the ‘‘white coat effect’’), reinterpreting pain in nonthreatening ways (e.g., as sensations) prompts patients to take fewer sedatives and leave the hospital sooner; and the health decline of cancer patients often has less to do with the actual course of the illness and more to do with their negative expectations regarding the disease (Langer, 1989). EXERCISE AND THE PLACEBO EFFECT As the most common health threats are now infectious rather than chronic, remedies have also changed. Doctors now prescribe behavioral changes such as exercise for chronic diseases like diabetes, heart disease, and even cancer. We wondered whether the well-known benefits of exercise are in whole or in part the result of the placebo effect. A positive finding would speak to the potentially powerful psychological control people have over their health. There is evidence supporting the idea that the placebo effect plays a role in occasioning the psychological benefits associated with exercise (Desharnais, Jobin, Cote, Levesque, & Godin, Address correspondence to Alia Crum or Ellen Langer, Department of Psychology, Harvard University, 1330 William James Hall, 33 Kirkland St., Cambridge, MA 02138, e-mail: [email protected] or [email protected]. When negative expectations are met with negative results, the placebo effect is often called the nocebo effect (Hahn, 1997). PSYCHOLOGICAL SCIENCE Volume 18—Number 2 165 Copyright r 2007 Association for Psychological Science 1993; Plante, Lantis, & Checa, 1998; Plante & Rodin, 1990). Desharnais et al. conducted an experiment on 48 healthy young adults engaged in a supervised 10-week exercise program. Half of the subjects (the experimental condition) were led to believe that the program was specifically designed to improve psychological well-being. The other half were not told anything about these benefits; instead, the emphasis was on the biological aspect of the program. Although the results showed similar increases in fitness in the two conditions, the subjects in the experimental condition showed a significant increase in selfesteem. Although studies have yet to investigate whether the perception of physical activity and resulting beliefs about one’s health have effects on the physiological benefits associated with physical activity, several studies allude to the possibility. Health perceptions have been related to actual health. For example, Kaplan and Camacho (1983), in a cohort study of 6,928 adults, found that perceived health was a better predictor of mortality than actual health. Idler and Kasl (1991) concluded that elderly persons who perceive their health as poor are 6 times more likely to die than those who perceive their health as excellent, regardless of actual health status. Further support for the possibility of the placebo effect in the benefits of exercise comes from the fact that the numerous studies linking exercise to health have generally relied on selfreported information to measure physical activity (Plante & Rodin, 1990); the results of these studies therefore reflect the relationship between health and perceived levels of physical activity, rather than actual levels. This raises the question of whether some of the positive gains of physical activity are due more to the perception of exercise and its association with health than to the actual performance of exercise. In the study we report here, we investigated the role of the placebo effect (the moderating role of mind-set) in the relationship between exercise and health. We hypothesized that the placebo effect plays a role in the health benefits of exercise: that one’s mind-set mediates the connection between exercise and one’s health. If this hypothesis is true, increasing perceived exercise, independent of actual exercise, would be expected to result in subsequent health benefits (a placebo effect).