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

Using the input-process-output (IPO) model as an organizing framework, this paper provides an overview of the literature on multiple dimensions of dietary supplement (DS) consumption. Based on a systematic review of 174 studies from different disciplines over two decades, we pinpointed the key topics that have been examined in this growing body of literature and identified the major themes within DS consumption. Moreover, we integrated the major themes in inputs, processes, and outputs to develop a comprehensive understanding of individuals' DS consumption behaviors, motivations, and social mechanisms underlying such behaviors. This research has implications for health consumption and promotion research. We identified DS consumption as a social-cultural process in which individuals practice lifelong self-learning and socialization activities through which lay health knowledge may be developed. Accordingly, their DS use motives may be related to health improvement or not (e.g. identity expressions), which are formed during interactions with various stakeholders in the health marketplace. When confronting the contemporary health promotion culture and self-care paradigm, it is important for researchers to deepen our knowledge of consumers' motives for DS consumption and the underlying social mechanisms to aid consumers' health consumption decisions and guide the multiple stakeholders in the health marketplace.