Marked Heterogeneity in Micronutrient Composition of Multivitamin–Mineral Supplements

Background Dietary research frequently assesses multivitamin–mineral (MVI) supplement use through broad categorical questions without specifying formulation details. This approach assumes substantial homogeneity across MVI products. This study quantified variation in micronutrient composition across commercially available MVI formulations to assess whether generic “MVI use” categorization is scientifically defensible. Methods Fifty commercially available MVI formulations from major U.S. online retailers were analyzed. For each formulation, the percent daily value (%DV) for 25 micronutrients was recorded (absent nutrients coded as 0% DV). For each micronutrient, inclusion rates, medians with interquartile ranges (Q1–Q3), and minimum–maximum ranges were calculated. Results MVI formulations exhibited marked heterogeneity in nutrient inclusion and dosing. Only folate and vitamin B12 were present in all 50 formulations. Several nutrients were absent in most products (e.g., choline absent in 78%, iron in 68%, phosphorus in 64%). Among included nutrients, ranges were often very wide, from 0% DV in some products to very high values in others (e.g., vitamin B12 up to 27,792% DV; thiamin up to 6,250% DV; vitamin E up to 893% DV). Conclusions MVI formulations constitute a highly heterogeneous exposure. Research that treats “multivitamin use” as a homogeneous category risks substantial exposure misclassification and attenuation of formulation-specific associations. Studies examining the health effects of MVI supplementation should specify the exact formulations or stratify by nutrient composition. This work motivates formulation-specific exposure definitions and composition-stratified analyses in nutritional epidemiology.