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Such mechanisms may stimulate the psychological state known as Fear of Missing
Out, defined as the apprehension that others might be experiencing rewarding
opportunities that one is absent from (Przybylski et al., 2013). In social commerce
environments, features such as real-time interaction indicators, viral content, and limited-
time promotions can intensify urgency and encourage faster purchasing decisions
(Mustikasari et al., 2025; Zhang et al., 2025). For health-related products like dietary
supplements, purchasing decisions may therefore be influenced not only by health needs
but also by social and psychological pressures created by digital consumption
environments. This phenomenon is particularly relevant for Generation Z, a cohort
characterized by intensive social media usage and strong engagement with digital
platforms. Previous research shows that 97.2% of participants use the Internet to search
for health information, and 72.6% have practiced self-medication based on online
information (Doan Anh Dung et al., 2024). However, online purchasing of dietary
supplements also presents risks such as counterfeit products, misleading information, and
limited regulatory oversight in digital markets.
Although previous studies have explored FOMO in social commerce, most have
focused on general consumer goods such as fashion or electronics. Research applying
health behavior theories to explain online purchasing of health-related products
remains limited, particularly in emerging markets like Vietnam. Therefore, this study
examines how FOMO influences Vietnamese Gen Z’s intention to purchase dietary
supplements online by integrating FOMO into the extended Health Belief Model within
the social commerce context.
2. Theoretical framework and research model
2.1. Theoretical framework
2.1.1. Health belief model (HBM) and extended health belief model (eHBM)
The Health Belief Model (HBM) (Rosenstock, 1966) explains health-related
behaviors based on individuals’ cognitive evaluations of several key perceptions, including
perceived susceptibility, perceived severity, perceived benefits, and perceived barriers.
Purchasing dietary supplements can be conceptualized as a preventive health behavior
aimed at reducing potential health risks and improving physical well-being (Siro et al.,
2008). Therefore, HBM provides a suitable theoretical framework for examining how
health beliefs among Generation Z shape their intention to purchase dietary supplements
online.
However, the traditional HBM has certain limitations in explaining complex and
sustained behaviors, particularly in digitally mediated consumption environments where
individuals actively seek information and interact with multiple online stimuli. To address
this limitation, Strecher and Becker (1988) extended the model by incorporating self-
efficacy, a concept derived from Social Cognitive Theory. Self-efficacy refers to an
individual’s confidence in their ability to perform a specific behavior. In the context of
online dietary supplement purchasing, this includes confidence in searching for health
information, evaluating product credibility, and completing online transactions. By
integrating self-efficacy, the extended Health Belief Model (eHBM) enhances the
explanatory power of HBM in understanding health-related decision-making in digital
environments. Therefore, this study adopts eHBM as the primary cognitive framework to
explain online purchase intention.
2.1.2. Self - determination Theory (SDT)
Self-Determination Theory (SDT) (Ryan & Deci, 1985, 2000) explains human

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