Chemistry Reference
In-Depth Information
phosphoenolpyruvate carboxykinase. The few manganese enzymes in higher
animals and humans include arginase, pyruvate carboxylase and manganese
superoxide dismutase. Manganese deficiency has been difficult to induce or
identify in humans, and thus is generally not considered to be of much nutri-
tional concern. The most likely case of manganese deficiency is that of a child
on long-term parenteral nutrition who exhibited diffuse bone demineralization
and poor growth that were corrected by manganese supplementation. Other
probable signs of manganese deficiency are a finely scaling, minimally erythe-
matous rash, decreased plasma cholesterol concentration and increased serum
alkaline phosphatase activity. Low dietary manganese or low blood and tissue
manganese have been associated with osteoporosis, diabetes, epilepsy, athero-
sclerosis, impaired wound healing and cataracts (Wedler, 1994). Findings from
animal experiments have provided some support for these associations. In the
past, manganese was considered to be one of the least toxic of the essential
mineral elements (Food and Nutrition Board: Institute of Medicine, 2001;
Nielsen, 2006). Recently, however, magnetic resonance imaging has shown
that signals for manganese in brain are strongly associated with neurological
symptoms (e.g., sleep disturbances) exhibited by patients with chronic liver
disease. Such findings suggest that high intakes of manganese are ill-advised
because of potential neurotoxicological effects, especially in people with com-
promised homeostatic mechanisms or infants whose homeostatic control of
manganese is not fully developed.
The FNB (Food and Nutrition Board: Institute of Medicine, 2001)
found no functional criteria of manganese status to use for establishing an
RDA for manganese for infants. Thus, they set AIs for manganese that
reflected the mean intake of infants fed principally human milk; these AIs
were 0.003 mg/d for age 0-6 months and 0.6 mg/d for age 6-12 months. Intake
data were used to determine AIs for other age groups (Table 10.2).
Manganese is fairly uniformly distributed in soft tissues at concentra-
tions generally less than 3 mg/g (Leach and Harris, 1997; Committee on
Minerals and Toxic Substances in Diets and Water for Animals, 2005).
Bone contains a substantial amount of manganese but should not be con-
sidered a reservoir. Serum or plasma manganese concentrations apparently
are somewhat sensitive to large variations in manganese intake, with normal
values near 1 mg/l (Food and Nutrition Board: Institute of Medicine, 2001).
Mean concentrations of manganese in human milk were found to be highest
during the first few days postpartum (6-12 mg/l); at 1 month it was found to be
approximately 4.0 mg/l, and apparently declined to near 2.0 mg/l by 3 months
postpartum (Food and Nutrition Board: Institute of Medicine, 2001). A
correlation between dietary intake and human milk concentration has been
reported (Vuori et al., 1980). The mean concentration of manganese in
mature bovine milk is 30 mg/l (Lonnerdal et al., 1981). The concentration in
