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With the increasing awareness of health and the widespread adoption of social media advertising, health food advertising has become an important source of information influencing consumer decision-making. However, existing studies have primarily focused on the effects of attitudes or behaviors, with limited attention to the underlying psychological mechanisms. Therefore, this study applies optimal arousal theory to examine how expertise and trustworthiness in health food advertising influence consumers’ purchase intention through perceived information relevance. The findings indicate that both expertise and trustworthiness positively affect perceived information relevance, which in turn significantly enhances purchase intention. These results suggest that individuals tend to pursue an optimal level of stimulation, and when advertising information evokes an appropriate level of psychological arousal and aligns with personal needs, it is more likely to facilitate positive behavioral responses. In addition to confirming the importance of perceived information relevance, this study extends optimal arousal theory from the level of sensory stimulation to the cognitive level, thereby advancing the development of optimal arousal theory research.

This article investigates the impact of social influence on online food delivery (OFD) purchase behavior in Vietnam, specifically examining the moderating role of trust and physical obstacles during the COVID-19 pandemic. A total of 378 respondents participated in the research, and the findings highlight the significance of social networks and interpersonal relationships in the OFD market. Regarding the role of trust as a moderator, the findings highlighting the importance of building trustworthiness and credibility in the OFD industry. The findings suggest that physical obstacles, such as the closure of non-essential stores and social distancing measures, weaken the influence of social factors on consumers' behavior. These changes in individuals' lifestyles have introduced physical barriers to traditional dining experiences, consequently increasing reliance on online food delivery (OFD) services. Overall, this study contributes to the existing literature on consumer behavior and provides insights for industry practitioners and policymakers to develop effective marketing and communication strategies and support mechanisms to facilitate the growth and sustainability of the online food delivery industry in Vietnam.