Analytical ingredient content and variability of adult multivitamin/mineral products: national estimates for the Dietary Supplement Ingredient Database

Abstract

Background: Multivitamin/mineral products (MVMs) are the dietary supplements most commonly used by US adults. During manufacturing, some ingredients are added in amounts exceeding the label claims to compensate for expected losses during the shelf life. Establishing the health benefits and harms of MVMs requires accurate estimates of nutrient intake from MVMs based on measures of actual rather than labeled ingredient amounts.

Objectives: Our goals were to determine relations between analytically measured and labeled ingredient content and to compare adult MVM composition with Recommended Dietary Allowances (RDAs) and Tolerable Upper Intake Levels.

Design: Adult MVMs were purchased while following a national sampling plan and chemically analyzed for vitamin and mineral content with certified reference materials in qualified laboratories. For each ingredient, predicted mean percentage differences between analytically obtained and labeled amounts were calculated with the use of regression equations.

Results: For 12 of 18 nutrients, most products had labeled amounts at or above RDAs. The mean measured content of all ingredients (except thiamin) exceeded labeled amounts (overages). Predicted mean percentage differences exceeded labeled amounts by 1.5-13% for copper, manganese, magnesium, niacin, phosphorus, potassium, folic acid, riboflavin, and vitamins B-12, C, and E, and by ∼25% for selenium and iodine, regardless of labeled amount. In contrast, thiamin, vitamin B-6, calcium, iron, and zinc had linear or quadratic relations between the labeled and percentage differences, with ranges from -6.5% to 8.6%, -3.5% to 21%, 7.1% to 29.3%, -0.5% to 16.4%, and -1.9% to 8.1%, respectively. Analytically adjusted ingredient amounts are linked to adult MVMs reported in the NHANES 2003-2008 via the Dietary Supplement Ingredient Database (http://dsid.usda.nih.gov) to facilitate more accurate intake quantification.

Conclusions: Vitamin and mineral overages were measured in adult MVMs, most of which already meet RDAs. Therefore, nutrient overexposures from supplements combined with typical food intake may have unintended health consequences, although this would require further examination.

Keywords: NHANES; Recommended Dietary Allowance (RDA); US Pharmacopeia; dietary supplement; multivitamins; overage; quality control; reference material; sampling plan; upper limit.

FIGURE 1

Adult multivitamin/mineral products were ordered by measured content of folic acid (A) and zinc (B) for intake per day (as recommended on product labels). A majority of products had overages in folic acid content and provided a daily intake above the RDA, but below the folic acid UL [as DFEs; 1 DFE = 1 μg food folate = 0.6 μg of folate from dietary supplements consumed with food (14)]. One-half of the products labeled above the folic acid UL also had measured overages, whereas the rest had measured folic acid below the label amount. Note that products with the same labeled amount of folic acid differ greatly in their actual content. A majority of products were labeled above the zinc RDA but significantly below the zinc UL, and the measured overages were very small. DFE, dietary folate equivalent; RDA, Recommended Dietary Allowance; UL, Tolerable Upper Intake Level.

FIGURE 2

Distributions of percentage differences between analytic and label ingredient amounts for minerals (A) and vitamins (B). The box plots show the 5th (lower circle), 10th (lower whisker), 25th (box bottom boundary), 50th (median, solid line), mean (dashed line), 75th (box top boundary), 90th (upper whisker), and 95th (upper circle) percentiles. Observations: calcium, n = 295; copper, n = 284; iodine, n = 250; iron, n = 200; magnesium, n = 280; manganese, n = 281; phosphorus, n = 188; potassium, n = 192; selenium, n = 282; zinc, n = 300; folic acid, n = 342; niacin, n = 338; riboflavin, n = 339; thiamin, n = 339; vitamin B-12, n = 337; vitamin B-6, n = 347; vitamin C, n = 329; and vitamin E, n = 320.

FIGURE 3

Regression plots showing relations between label ingredient amounts and percentage differences from label for analytically measured mineral(A) and vitamin (B) content. Solid lines indicate the mean predicted percentage differences. Dark-gray belts represent 95% CIs for the predicted meanpercentage differences. Light-gray belts represent 95% CIs for the predicted individual observation percentage differences from label. Relations between thelabel and percentage difference from label were estimated by regression with the SAS mixed-model procedure (SAS software version 9.3, SAS Institute, Inc.Cary, NC). The selected regression equations were used to predict mean analytic concentrations for each ingredient in adult multivitamin/mineral products:label value 3 (1 + predicted percentage difference/100). See detailed statistical methods in the Supplemental Methods.

FIGURE 3

Regression plots showing relations between label ingredient amounts and percentage differences from label for analytically measured mineral(A) and vitamin (B) content. Solid lines indicate the mean predicted percentage differences. Dark-gray belts represent 95% CIs for the predicted meanpercentage differences. Light-gray belts represent 95% CIs for the predicted individual observation percentage differences from label. Relations between thelabel and percentage difference from label were estimated by regression with the SAS mixed-model procedure (SAS software version 9.3, SAS Institute, Inc.Cary, NC). The selected regression equations were used to predict mean analytic concentrations for each ingredient in adult multivitamin/mineral products:label value 3 (1 + predicted percentage difference/100). See detailed statistical methods in the Supplemental Methods.