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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
VAST Study Team, 1993; Loyd-Puryear et al., 1991; Rahmathullah et al., 1990; Salazar-Lindo et al., 1993; West et al., 1991).
An EAR of 300 μg RAE/day can be calculated based on the dark adaptation data obtained from 13 individuals from four studies on adults (Table 4-4). The duration of depletion and repletion varied among these four studies and the majority of the studies were conducted on men. Interpolation of the level of vitamin A at which dark adaptation of each individual was corrected in these four studies results in a median intake of 300 μg RAE/day, which can be used to set an EAR based on dark adaptation for adults. Using this method, there was insufficient evidence to support setting a different EAR for men and for women, as there were too few women studied. EARs using dark adaptation as the indicator for children (1–3 years, 112 μg RAE/day; 4–8 years, 150 μg RAE/day; 9–13 years, 230 μg RAE/day) and adolescents (14–18 years, 300 μg RAE/day) are based on extrapolation from the adult EAR as described in Chapter 2.
INTAKE OF VITAMIN A
Common dietary sources of preformed vitamin A in the United States and Canada include liver, dairy products, and fish. Chug-Ahuja et al. (1993) reported that carrots were the major contributor of β-carotene (25 percent). Other major contributors to β-carotene intakes included cantaloupe, broccoli, squash, peas, and spinach. Carrots were also the major contributor (51 percent) of α-carotene. Fruits were the sole contributors of β-cryptoxanthin. According to data collected from the 1994–1996 Continuing Survey of Food Intakes by Individuals (CFSII), the major contributors of vitamin A from foods were grains and vegetables (approximately 55 percent), followed by dairy and meat products (approximately 30 percent).
The Third National Health and Nutrition Examination Survey (NHANES III) (Appendix Table C-8) estimated that the median dietary intake of vitamin A is 744 to 811 μg/day for men and 530 to 716 μg/day for women using the new provitamin A carotenoid conversion factors for calculating retinol activity equivalents (RAE) (see Table 4-3). When one examines Appendix Table C-8 to determine the proportion of individuals with intakes that were less than the EAR (500 μg RAE/day for women and 625 μg RAE/day for men), it