Nationwide Online Survey Method to Estimate Ongoing Adverse Events Caused by Supplement Use: Application to Diarrhea

The current adverse event reporting systems are inadequate to prevent potential health damage caused by dietary supplement use, and a better case-collecting system is needed. The aim of this study was to examine whether online surveys would be a useful methodology for estimating ongoing adverse events, focusing on diarrhea as a model symptom. We used four online survey companies and requested that they administer the same questionnaire to their registrants regarding experiences of adverse events associated with supplement use and details of diarrhea symptoms, as well as the product and ingredient names of suspected supplements. Of 78,220 dietary supplement users, 9% to 25% reported experiencing adverse events in the previous year. A total of 723 participants who answered affirmatively about a putative causal relationship between supplement use and the onset of diarrhea and who clearly identified the product and/or ingredient were eligible for final analysis. Comparisons among the survey companies showed differences in the proportions of reported symptoms; however, the rank orders were consistent in the preliminary survey. Also, when analysis was limited to specific participants from a full-scale survey, even the numerical values of the proportions were consistent among the four companies. Herbal/botanical ingredients, specifically Coleus forskohlii, were the ingredients most frequently reported to be associated with diarrhea. These results indicate that online survey can be a useful method to complement the current system for estimating ongoing adverse events and identifying the responsible supplements.