Background: The aim of this study was to screen the prevalence of supplement use in Swiss fitness center users and what information sources they consulted. Methods: Customers of 10 fitness centers were screened with a quantitative questionnaire. Results: Eighty two percent of the 417 fitness center users consumed at least one supplement per week. Supplement intake correlated with training frequency (rs = 0.253, p
< 0.001). The most prevalent products were protein supplements (used by 49% of the study population), magnesium (34%), and multi-micronutrient supplements (31%). The average number of supplement servings per week among consumers was 17.1 (SD: 16.1, median: 11.0) and the average number of different products used was 6.9 (SD: 4.4, median: 6.0). The most frequently used information sources were the coach/trainer (28%), the website of the supplement seller (26%), and training peers (24%). Thirty seven percent were informed or informed themselves about potential risks associated with the supplement used. The leading reasons for selecting the information source were the desire for scientific-based information followed by the education level of the informing person. Conclusions: A high prevalence of supplement intake among Swiss fitness center users was associated with a low level of information quality and a low prevalence of risk information. A discrepancy between a desire for high quality evidence-based information and a contrasting behavior was detected.
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