ARS | Publication request: To err may be human, but IU calculations for provitamin A carotenoids in the USDA national nutrient database are not in error

Submitted to: American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 11, 2007
Publication Date: April 20, 2008
Citation: Yates, A.A., Holden, J.M., Gebhardt, S.E., Murphy, S.P. 2007. To err may be human, but IU calculations for provitamin A carotenoids in the USDA national nutrient database are not in error. American Journal of Clinical Nutrition. 87(4):1068.

Interpretive Summary: This article is an invited reply to a letter to the editor of the American Journal of Clinical Nutrition in which the authors allege that an error exists in the method used to calculate Vitamin A values in international units (IU) in the USDA National Nutrient Database for Standard Reference (SR). It urges that USDA decrease by a factor of six the IU values listed for plant sources of beta-carotene to take into account the relatively poor bioavailability of plant sources of vitamin A. The authors, however, have misunderstood both the definition and the appropriate use of this measure of vitamin A activity. The IU, used in the U.S. for vitamin A recommendations until 1974, was defined by the World Health Organization in the 1940s, and the IU values in the SR follow exactly this definition of an IU, and thus are not in error. Since the Food and Drug Administration (FDA) continues to use vitamin A in IUs as the unit of measure for nutrition and dietary supplement labeling, the database provides this information. However, it also provides the vitamin A activity in the current unit of activity, the retinol activity equivalent (RAE), which does take into account the most recent evaluation of the relative biological availability and activity of plant sources of vitamin A. Users of the database are urged to use this value when assessing diets of individuals and groups, as the only use of the information in IU as described in the documentation of the database is for nutrition labeling. Since the FDA is currently in the process of rulemaking to update the information on nutrition on the label, it is suggested that the concerns of scientists regarding the use of the IU be directed toward the FDA during its rule-making process.

Technical Abstract: This article is an invited reply to a letter to the editor of the American Journal of Clinical Nutrition in which the authors allege that an error exists in the method used to calculate Vitamin A values in international units (IU) in the USDA National Nutrient Database for Standard Reference (SR). It urges that USDA decrease by a factor of six the IU values listed for plant sources of beta-carotene to take into account the relatively poor bioavailability of plant sources of vitamin A. The authors, however, have misunderstood both the definition and the appropriate use of this measure of vitamin A activity. The IU, used in the U.S. for vitamin A recommendations until 1974, was defined by the World Health Organization (WHO) in the 1940s, and the IU values in the SR follow exactly this definition of an IU, and thus are not in error. The IU is defined by WHO as follows: 1 IU = 0.3 micrograms retinol, 0.6 micrograms beta-carotene, or 1.2 micrograms other provitamin carotenoids. Since the Food and Drug Administration (FDA) continues to use vitamin A in IUs as the unit of measure for nutrition and dietary supplement labeling, the database provides this information. However, it also provides the vitamin A activity in the current unit of activity, the retinol activity equivalent (RAE), which does take into account the most recent evaluation of the relative biological availability and activity of plant sources of vitamin A. The database also provides the content of retinol, beta-carotene, alpha-carotene, and beta-cryptoxanthin in micrograms. Users of the database are urged to use the RAE values when assessing diets of individuals and groups for vitamin A, as the only use of the information in IU as described in the documentation of the database is for nutrition labeling. Since the FDA is currently in the process of rulemaking to update the information on nutrition on the label, it is suggested that the concerns of scientists regarding the use of the IU be directed toward the FDA during its rule-making process.