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An error in the US Department of Agriculture nutrient database results in vitamin A values that are 6 times too high

Linus Pauling Institute
Oregon State University
571 Weniger Hall
Corvallis, OR 97331
E-mail: balz.frei{at}oregonstate.edu

Lisa M Bouley

Nutritionist (private practice)
Medford, MA

Dear Sir:

We wish to inform the readership of the Journal of a serious error in the vitamin A values listed in the US Department of Agriculture (USDA) National Nutrient Database for Standard Reference (1). These values not only are used by scientists, educators, and the general public, but also are the foundation of other nutrient databases and of information listed on the Nutrition Facts panel of food labels (2). Therefore, the accuracy of the data in the USDA nutrient database has important implications for nutritional epidemiology, national food policies, and public health.

The listings in the USDA nutrient database for international units (IU) of vitamin A for carotenoid-containing foods are 6 times too high because bioavailability was not taken into account. For these foods, the USDA is using a conversion factor of 0.6 µg β-carotene = 1 IU vitamin A, which should be used only for oil-based supplements (3). The correct conversion factor should be 3.6 because, in 2001, the Institute of Medicine stated that 12 µg dietary β-carotene = 1 µg retinol, and 0.3 µg retinol = 1 IU vitamin A [see Table 4-3 (3)]. Therefore, 3.6 µg β-carotene in foods = 1 IU vitamin A.

Using the entry in the USDA nutrient database for cantaloupe as an example (NDB No. 09181; values are for 100 g), 2020 µg β-carotene ÷ 0.6 = 3367 IU vitamin A, and the sum of β-carotene and other carotenoids is listed as 3382 IU vitamin A (1). Using the correct conversion factor—ie, 3.6—instead of a factor of 0.6 gives 2020 µg β-carotene ÷ 3.6 = 561 IU vitamin A.

Another method to derive the number of IU of vitamin A is to convert the retinol activity equivalents (RAE) to IU. For example, in the USDA nutrient database, the RAE for 100 g cantaloupe is 169 µg RAE, and 169 x 3.33 IU/RAE = 563 IU vitamin A [see Table 4-3 (3): 1 µg all-trans retinol = 1 µg RAE = 3.33 IU vitamin A]. Thus, approximately the same number (561 or 563, respectively) of vitamin A IU is obtained by either calculating it directly from µg dietary β-carotene or first converting µg dietary β-carotene to RAE and then to IU of vitamin A. Using either method, the IU values obtained for vitamin A are one-sixth of those listed in the USDA nutrient database (1).

This error has serious consequences for vitamin A values listed on Nutrition Facts panels. For example, a Nutrition Facts panel for carrots states that one serving (128 g) provides 430% of the daily value (DV) for vitamin A. In fact, one serving provides only one-sixth of that—ie, 72% of the DV—for vitamin A. It is interesting that 430% of the DV for vitamin A would be more than twice the tolerable upper intake level (UL) of vitamin A (3). We recognize that the UL refers to preformed vitamin A (retinol) and not to carotenoids, but the consumer, for whom the Nutrition Facts panels are intended, may not readily make this distinction and may be confused by a vitamin A value that exceeds the UL.

In summary, the vitamin A IU values for carotenoid-containing foods listed in the USDA National Nutrient Database for Standard Reference (1) are incorrect because an incorrect conversion factor was used to calculate these values. The currently listed data use a conversion factor that treats β-carotene from foods as if it were from oil-based supplements and use the assumption that 2 µg β-carotene = 1 µg retinol. However, current knowledge is that 12 µg β-carotene in foods = 1 µg retinol (3). Thus, the conversion factor should be 3.6 µg dietary β-carotene = 1 IU vitamin A. We have notified the USDA of this error in its nutrient database and have urged the USDA to correct the error as soon as possible.

ACKNOWLEDGMENTS

None of the authors had a personal or financial conflict of interest.

REFERENCES

1. US Department of Agriculture, Agricultural Research Service. USDA nutrient database for standard reference, release 20. Internet: http://www.nal.usda.gov/fnic/foodcomp/search (accessed 23 October 2007).
2. Holden JM, Harnly JM, Beecher GR. Food composition. 9th ed. In: Bowman BA, Russell RM, eds. Present knowledge in nutrition, vol 2. Washington, DC: ILSI Press, 2006:781–94.
3. Food and Nutrition Board, Institute of Medicine. Dietary reference intakes for vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc. Washington, DC: National Academy Press, 2001.

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