Development and Validation of Questionnaires for Quantifying Intake from Dietary Supplements: A Scoping Review

Dietary supplements (DSs) contribute substantially to total nutrient intake. However, DS questionnaires differ in format and development practices, which can introduce distinct patterns of measurement error and complicate accurate estimation of both intake and prevalence.

This study aimed to scope and describe questionnaires that quantify nutrient intake from DS, describing questionnaire formats (closed-ended, mixed-type), development procedures (DS classification, composition sources, default-value rules, and missing-data handling), and their validity and reproducibility.

PubMed and Web of Science databases were searched. Eligible questionnaires were those that could independently quantify DS intake and for which development and/or validation compared with a reference (inventory, 24-h recalls/dietary records, and biomarkers) were reported. Open-ended (record-like) questionnaires were excluded. We extracted development procedures and presented them descriptively. Validation results were summarized by nutrient/DS type, intake type (DS-only; total from foods/beverages plus DS), and questionnaire format-using relative differences (intake, prevalence) and correlation coefficients. Results of reproducibility were extracted when reported.

Of 14,529 records, 15 eligible questionnaires (6 closed-ended and 9 mixed-type) were included, and 13 were validated. Reference methods included 24-h recalls/dietary records (n = 9), biomarkers (n = 6), and inventory (n = 4). On average, the questionnaires tended to overestimate DS-only and total (mixed-type only) intake. Correlation coefficients with intake-based references (24-h recalls/dietary records) were generally moderate to high for both DS-only and total intake, except for iron, which was negligible. However, for mixed-type questionnaires, correlations for total intake were lower than for DS-only. Closed-ended questionnaires more often overestimated the prevalence of DS users relative to reference methods, whereas mixed-type questionnaires showed the opposite pattern-slightly underestimating compared with inventory and overestimating compared with 24-h recalls/dietary records. Development procedures were frequently incompletely reported.

Overall performance varied by format, nutrient, intake type, and reference method. To improve comparability and policy utility, standardized DS classification and transparent reporting of development procedures are needed.