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assessment of status when typical amounts of manganese are consumed.

Arginase Activity

Arginase is depressed in the livers of manganese-deficient rats (Paynter, 1980). Brock and coworkers (1994) noted that manganese-deficient rats also had depressed plasma urea and elevated plasma ammonia concentrations. Arginase is affected by a variety of factors, however, including high protein diet and liver disease (Morris, 1992).

Manganese-Superoxide Dismutase Activity

Manganese-deficient animals have low manganese-superoxide dismutase (MnSOD) activity (Davis et al., 1992; Malecki et al., 1994; Zidenberg-Cherr et al., 1983). Davis and Greger (1992) demonstrated that lymphocyte MnSOD activity was elevated in 47 women supplemented with 15 mg/day of manganese for more than 90 days. However, other factors like ethanol (Dreosti et al., 1982) and dietary polyunsaturated fatty acids (Davis et al., 1990) may affect MnSOD activity. A fairly large blood sample is required to measure lymphocyte MnSOD.

FACTORS AFFECTING THE MANGANESE REQUIREMENT

Bioavailability

Prior intakes of manganese and of other elements, such as calcium, iron, and phosphorus, have been found by some investigators to affect manganese retention (Freeland-Graves and Lin, 1991; Greger, 1998; Lutz et al., 1993). Adding calcium to human milk significantly reduced the absorption of 54Mn from 4.9 to 3.0 percent (Davidsson et al., 1991). Low ferritin concentrations are associated with increased manganese absorption, therefore having a gender effect on manganese bioavailability (Finley, 1999).

Sandstrom and coworkers (1990) gave a multimineral supplement that included 18 mg of iron, 15 mg of zinc, and 2.5 mg of manganese for a minimum of 30 weeks. Neither whole blood manganese concentration nor superoxide dismutase activity was increased significantly from baseline with supplementation. Seven healthy volunteers subsequently consumed a tracer dose containing 54Mn, 75Se, and 65Zn. Manganese absorption was only 1 percent of the oral dose. Sandstrom and coworkers (1987) reported a higher rate of



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