Determinants of knowledge about dietary supplements among Polish Internet users with no medical education: a nationwide cross-sectional study

BACKGROUND: Having an accurate understanding of dietary supplements is a prerequisite for informed decision regarding their intake. However, there is a need for studies of such understanding among the public based on validated research tools. OBJECTIVE: To assess the knowledge about dietary supplements in Polish Internet users with no medical education, to identify its determinants and design an appropriate predictive model. METHODS: The study protocol with statistical analysis plan was prospectively registered. Polish users of an online health service and a social networking service were administered a survey consisting of the recently-developed Questionnaire on Knowledge about Dietary Supplements, Questionnaire on Trust in Advertising Dietary Supplements, Beliefs about Medicines Questionnaire, as well as several other health related single-item measures and sociodemographic questions. The results were subjected to general linear modeling. RESULTS: In total, 6273 participants were included. Out of 17 yes/no questions in the Questionnaire of Knowledge about Dietary Supplements, the mean number of correct responses was 9.0 (95% CI: 8.9 to 9.1). Health service users performed worse than social networking ones by 2.3 (95% CI: 2.1 to 2.5) points in an analysis adjusted for potential confounders. Internet users had less true beliefs about dietary supplements if they presented higher trust in their advertising (adjusted β: -.37, 95% CI: -.39 to -.34), used dietary supplements (adjusted β: -.14, 95% CI: -.17 to -.12), experienced their positive effect (adjusted β: -.16, 95% CI: -.18 to -.13), were older or younger than 35 (adjusted β: -.14, 95% CI: -.17 to -.12), expressed interest in the topic of dietary supplements (adjusted β: -.10, 95% CI: -.13 to -.08), reported getting information about the products from friends (adjusted β: -.13, 95% CI: -.15 to -.11), believed that medicines are harmful (adjusted β: -.12, 95% CI: -.15 to -.10). The proposed 5-predictor model could explain 31.2% of variance in knowledge about dietary supplements. The model appeared resistant to overfitting and was able to forecast the majority of the observed associations. CONCLUSIONS: Polish Internet users with no medical education exhibit some false beliefs regarding dietary supplements. Trusting in advertising dietary supplements appears in conflict with having knowledge about them. There is an urgent need for effective online educational campaigns about dietary supplements and promotion of advertising literacy. The proposed predictive model, after being externally validated, may help identify the least informed target audience. CLINICALTRIAL: Open Science Framework, https://osf.io/5e92d/