Marked Heterogeneity in Micronutrient Composition of Multivitamin Supplements [Dataset]

Background: Dietary research commonly assesses multivitamin (MVI) supplement use through broad categorical questions that assume products are compositionally similar. This study quantified how much the micronutrient composition of best-selling MVI products varies, to assess whether treating “multivitamin use” as a single exposure category is defensible. Methods: The 100 best-selling multivitamin products on Amazon, the dominant U.S. online supplement retailer, were screened on July 24, 2026. After excluding children’s, adolescent, prenatal, single-nutrient, and condition-specific products and duplicate listings, 64 adult general multivitamins remained. For each product, the labeled percent Daily Value (%DV) of 25 micronutrients was recorded directly from the Supplement Facts panel. Heterogeneity was characterized along three axes: composition breadth (number of nutrients included), per-nutrient content (inclusion rate, median, interquartile range, and range), and megadosing (defined a priori as ≥1000% DV). Results: Composition breadth ranged from 7 to 24 of 25 nutrients (median 20). Only vitamin D, folate, and vitamin B12 were present in all 64 products, whereas choline, phosphorus, and iron were present in 22% or fewer. Labeled content varied widely; vitamin B12 ranged from 100% to 33,333% DV (median 408%). Thirty products (47%) contained at least one megadosed nutrient, concentrated in the B-complex vitamins and biotin. Conclusion: Best-selling multivitamins vary markedly in which nutrients they contain, in how much, and in whether they megadose. “Multivitamin use” is a compositionally heterogeneous exposure; studies should specify formulations or stratify by composition.