This study examined the relationship between not self-determined / self-determined solitude and stress responses, as well as the effect of supporting / thwarting of basic psychological needs. The sample consisted of 606 Japanese people aged 20 years and older. We used a cross-sectional survey to measure their motivations for solitude, supporting / thwarting of basic psychological needs, and stress responses. Not self-determined solitude was negatively correlated with supporting of basic psychological needs and positively correlated with thwarting of basic psychological needs. In addition, a cutoff score of 16 for not self-determined solitude was found to be optimal for identifying individuals with a high stress response. Mediation analysis revealed that supporting / thwarting of basic psychological needs has direct effects on stress responses and indirect effects mediated by not self-determined solitude. These findings suggest that fostering environments that support basic psychological needs of autonomy, competence, and relatedness can alleviate not self-determined solitude and reduce stress responses.
