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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
Identification of a No-Observed-Adverse-Effect Level (NOAEL) and a Lowest-Observed-Adverse-Effect Level (LOAEL). A LOAEL of 60 mg/day of supplemental iron salts was identified on the basis of a controlled, double-blind study by Frykman and coworkers (1994). They evaluated GI effects in 97 Swedish adult men and women after intake of either a nonheme iron supplement (60 mg/day as iron fumarate), a supplement containing both heme iron and nonheme iron (18 mg/ day, 2 mg from porcine blood and 16 mg as iron fumarate), or a placebo. The groups were similar with respect to gender, age, and basic iron status. The frequency of constipation and the total incidence of all side effects were significantly higher among those receiving nonheme iron than among those receiving either the combination of heme and nonheme iron or the placebo (Table 9-18). Although most of the reported GI effects were minor, five individuals found them to be severe enough to stop taking the medication. Four of these withdrawals occurred during the nonheme-containing iron treatment and one occurred just after changing from the nonheme-containing iron treatment to the placebo.
To estimate a LOAEL for total iron intake, the LOAEL for supplemental ferrous fumarate intake of 60 mg/day for Swedish men and women was added to 11 mg/day, the estimated mean iron intake from food in women from six European countries (Van de Vijver et al., 1999) and in men from Denmark (Bro et al., 1990). The LOAEL for total intake is therefore approximately 70 mg/day (11 + 60). It was not possible to identify a NOAEL based on the data on GI effects. Therefore, the LOAEL of 70 mg/day was used to derive a UL. There is supportive evidence for a LOAEL of 50 to 120 mg/day of supplemental iron salts from several other prospective studies (Brock et al., 1985; Coplin et al., 1991; Liguori, 1993; Lokken and Birkeland, 1979). However, these studies either failed to include a placebo control or contained fewer subjects than the study by Frykman and coworkers (1994).
Uncertainty Assessment. An uncertainty factor (UF) of 1.5 was selected to account for extrapolation from a LOAEL to a NOAEL. Because of the self-limiting nature of the observed GI effects, a higher UF was not justified.
Derivation of a UL. The LOAEL of 70 mg/day was divided by a UF of 1.5 to obtain a LOAEL and UL value of 45 mg/day of iron, after rounding.