Applications of the Theory of Planned Behavior to Consumption of Dietary Supplements and Other Health-related Behaviors
The purpose of this study was to review applications of Ajzen's Theory of Planned Behavior (TPB) to health behaviors, and to examine the efficacy of the TPB in predicting health-related behaviors. Further, the authors attempted to determine the usefulness of using the TPB to predict dietary supplement consumption. Other health behaviors reviewed included addictive behaviors, automobile-related behavior, clinical screening behavior, exercising behavior, HIV/AIDS-related behavior, oral hygiene behavior, and eating behavior. To date, several studies have used the TPB to predict eating behavior, but few have focused on consumption of dietary supplements. Peer-reviewed literature from 1980 to 2005 was attained using on-line search engines (MEDLINE, ERIC, PsycINFO, and PsycLIT). Articles using additional constructs (i.e. past behavior, self-esteem, etc) to explain variance in behavior or behavioral intention were not included. Average variance explained by the TPB was approximately 41% for behavioral intention and 27% for behavior. Attitude toward the behavior and perceived behavioral control were most often the primary constructs responsible for explained variance in behavioral intention. Perceived behavioral control independently predicted an average of 11% of behavioral variance. Overall, subjective norm was found to be a weak predictor of behavioral intention and behavior. Research suggests better measurement techniques and an expansion of the normative component is required to improve the predictive ability of the subjective norm construct. Research has demonstrated that the TPB is quite effective at predicting behavioral intention across health-related behaviors with attitude and perceived behavioral control being equally important. However, the TPB's predictions of behavioral intention do not always correlate to behavior. Additionally, the efficacy of the TPB varies between health-related behavioral categories. Suggestions will be made regarding further exploration and application of the TPB related to eating behaviors including dietary supplement consumption.