Submitted to: Analytical and Bioanalytical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2007
Publication Date: 9/20/2007
Citation: Andrews, K., Schweitzer, A., Zhao, C., Holden, J.M., Roseland, J.M., Brandt, M., Dwyer, J., Picciano, M., Saldanha, L., Fisher, K., Yetley, E., Betz, J., Douglass, L. 2007. The caffeine content of dietary supplements commonly purchased in the U.S.: Analysis of 53 products having caffeine-containing ingredients. Analytical and Bioanalytical Chemistry. 389(1): 231-239.
Interpretive Summary: While many people may know that foods and beverages such as coffee, tea, cola, and chocolate contain caffeine, they may not be aware that some dietary supplement ingredients contain caffeine (e.g., guarana, yerba mate, kola nut, and green tea extract). This manuscript documents the process used to identify representative caffeine-containing dietary supplements commonly purchased in the U.S and analyze these products for their caffeine level. Two or 3 lots of each representative product were purchased and analyzed using high pressure liquid chromatography (HPLC) in a commercial laboratory. Each analytical run included 1 or 2 National Institute of Standards and Technology (NIST) Standard Reference Materials (SRMs) with known levels of caffeine and two products in duplicate. The SRM results combined with consistent results from the analysis of the duplicated products indicate that the method of analysis used was accurate and precise and gives confidence in the product results obtained in this study. Caffeine intakes per serving and per day were calculated using the maximum recommendations for use on each product label. For the 53 products analyzed in this study, a wide range of caffeine levels (resulting in intakes of 1 to >800 mg/day) was documented. For products having a label amount for comparison (n=28), 89% had analytically based caffeine levels/day within 20% of the amount indicated on the package. This manuscript describes sample handling procedures for dietary supplements sold as tablets, capsules, and soft-gels. It also documents an important use for NIST SRM 3244, Ephedra-Containing Protein Powder and NIST SRM 3243, Ephedra-Containing Solid Oral Dosage Form. The matrices for these SRMs are common dietary supplement matrices and the caffeine levels are representative of the levels in products commonly sold in the U.S. These materials are excellent tools for the development of accurate methods of analysis and for method validation for caffeine in dietary supplements.
Technical Abstract: As part of a study initiating the development of an analytically validated Dietary Supplement Ingredient Database (DSID) in the United States (U.S.), a selection of dietary supplement products were analyzed for their caffeine content. Products sold as tablets, caplets, or capsules and listing at least one caffeine-containing ingredient (including botanicals such as guarana, yerba mate, kola nut, and green tea extract) on the label were selected for analysis based on market share information. Two or 3 lots of each product were purchased and analyzed using high pressure liquid chromatography (HPLC). Each analytical run included 1 or 2 National Institute of Standards and Technology (NIST) Standard Reference Materials (SRMs) and two products in duplicate. Caffeine intake per serving and per day was calculated using the maximum recommendation for use on each product label. Laboratory analysis for 53 products showed product means ranging from 1 to 829 mg caffeine/day. For products having a label amount for comparison (n=28), 89% (n=25) of the products had analytically based caffeine levels/day between -16% and +16% of the claimed levels. Lot-to-lot variability (n=2 or 3) for caffeine in most products (72%) was less than 10 percent.