Why and how do consumers use dietary supplements? A systematic review and thematic analysis.

This article systematically reviews 174 interdisciplinary studies on dietary supplement (DS) consumption using the input-process-output (IPO) model to organize key themes related to individuals’ DS behaviors, motivations, and social mechanisms. It identifies inputs such as individual health knowledge, marketplace influences, social networks, and government regulation; processes including purchase decisions, actual use, and socialization within families and communities; and outputs encompassing perceived health improvements, health motivation, and identity expression. The review highlights DS consumption as a dynamic, context-dependent sociocultural practice shaped by multiple stakeholders and emphasizes the need for improved consumer health literacy, ethical marketing, and regulatory oversight. It also calls for future research to explore the socialization processes and diverse outcomes of DS use to better inform health promotion and consumer decision-making.