absorption from this dose in subjects without prior consumption of a supplement, but high interindividual variability of manganese absorption and other potential confounders would require a study specifically designed to test the effect of prior supplementation on 54Mn absorption.
Davidsson and coworkers (1995) administered 54Mn in either a soy-based infant formula or a similar dephytinized formula to eight men and women. The geometric mean manganese absorption was 0.7 percent for the native formula and 1.6 percent for the dephytinized formula. Therefore, the presence of phytate reduced the efficiency of absorption of manganese.
Johnson and colleagues (1991) reported that manganese absorption did not significantly differ between plant foods that were extrinsically or intrinsically labeled with 54MnCl2. Absorption of 54Mn from a meal, extrinsically labeled with 54MnCl2, was significantly higher (8.9 percent) than the absorption of 54Mn from lettuce (5.2 percent), spinach (3.8 percent), wheat (2.2 percent), or sunflower seeds (1.7 percent). Absorption of 54MnCl2 did not differ whether the dose was 0.53 or 1.24 mg (7 to 10 percent).
Finley and coworkers (1994) reported that men absorbed significantly less manganese than women and that this difference may be related to iron status. A subsequent study specifically demonstrated that high ferritin concentrations were associated with reduced 54Mn absorption (Finley, 1999). Serum ferritin concentrations are higher in men (Appendix Table G-3) and therefore may affect, in part, the lower bioavailability of manganese observed in men.
No functional criteria of manganese status have been demonstrated that reflect response to dietary intake in infants. Thus, recommended intakes of manganese are based on an Adequate Intake (AI) that reflects the observed mean manganese intake of infants principally fed human milk.