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Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc
TABLE 4-1 Relative Absorption of Vitamin A and Supplemental β-Carotene
Depletion/repletion study; depletion phase ranged from 18 to 22 mo and the repletion phase ranged from 3 wk to 6 mo
Sauberlich et al., 1974
2 or 4 men per treatment group, United States
Depletion/repletion study; depletion phase ranged from 361 to 771 d and the repletion phase ranged from 2 to 455 d
a Treatment group received supplemental vitamin A or β-carotene.
b Based on the assumption that 1 IU is equivalent to 0.3 μg of vitamin A (WHO, 1950).
c One IU is equivalent to 0.6 μg of β-carotene (Hume and Krebs, 1949).
in oil, in individual foods, and as part of a mixed vegetable and fruit diet. Many of the earlier studies analyzed the fecal content of β-carotene after the consumption of a supplement, fruit, or vegetable. Data from these studies were not considered because the portion of unabsorbed β-carotene that is degraded by the intestinal microflora is not known. The efficiency of absorption of β-carotene in food is lower than the absorption of β-carotene in oil by a representative factor of a. Assuming that after absorption of β-carotene, whether from oil or food, the metabolism of the molecule is similar and that the retinol equivalency ratio of β-carotene in oil is 2:1, the vitamin A activity of β-carotene from food can be derived by multiplying a by 2:1.
Until recently it was thought that 3 μg of dietary β-carotene was equivalent to 1 μg of purified β-carotene in oil (NRC, 1989) due to a relative absorption efficiency of about 33 percent of β-carotene from food sources. Only one study has compared the relative absorption of β-carotene in oil versus its absorption in a principally mixed vegetable diet in healthy and nutritionally adequate individuals (Van het Hof et al., 1999). This study concluded that the relative absorption of β-carotene from the mixed vegetable diet compared to β-carotene in oil is only 14 percent, as assessed by the increase in plasma β-carotene concentration after dietary interven-
