Chemistry Reference
In-Depth Information
(0.02%) (Wheeler et al., 1983). The concentration of iodine is higher in whey
cheeses than in casein cheeses (Dahl et al., 2003).
10.12.
Molybdenum
Molybdenum is essential for the synthesis of a molybdenum co-factor
containing a pterin nucleus that is required for the activity of sulfite oxidase,
xanthine dehydrogenase and aldehyde oxidase in higher animals and
humans (Nielsen, 2006). These enzymes catalyze the conversion of sulfite
to sulfate, the transformation of hypoxanthine to xanthine and the oxida-
tion and detoxification of various pyrimidines, purines and pteridines.
Nutritional molybdenum deficiency has not been identified unequivocally
in humans other than in one individual nourished by total parenteral nutri-
tion (Abumrad et al., 1981). Thus, molybdenum generally is considered to
be of no practical nutritional concern for humans. The individual fed by
parenteral nutrition and individuals with genetic molybdoenzyme deficien-
cies (Johnson, 1997) have enabled the description of signs and symptoms of
molybdenum deficiency; these include hypermethioninemia, hypouricemia,
hyperoxypurinemia, hypouricosuria, low sulfate excretion and mental dis-
turbances. Inadequate data exist to identify any adverse health outcomes
caused by excessive molybdenum intake by normal, apparently healthy
individuals.
The FNB (Food and Nutrition Board: Institute of Medicine, 2001)
found no functional criteria on which to base a RDA for infants. Thus,
they set AIs for molybdenum that reflected the mean intake of infants fed
principally human milk; these AIs were 2 mg/d for age 0-6 months and 3 mg/d
for age 7-12 months. Extrapolation from the RDA for adults was the basis
for setting RDAs for children (Table 10.2).
Concentrations of molybdenum in tissues, blood and milk vary with
molybdenum intake (Committee on Minerals and Toxic Substances in Diets
and Water for Animals, 2005). Highest concentrations of molybdenum are
found in liver, kidney and bone (normally
>
1 mg/kg dry weight) (Johnson,
1997). The concentration of molybdenum in other tissues usually is between
0.14 and 0.20 mg/kg dry weight (Committee on Minerals and Toxic Sub-
stances in Diets and Water for Animals, 2005). Molybdenum concentration
decreases rapidly in human milk with stage of lactation; for example, in a
study of full-term infants, the median concentration of molybdenum in
mothers' milk fell from 4 mg/l at 1 week postpartum to nearly undectable
levels by 12 weeks postpartum (Friel et al., 1999). Another study found
postpartum concentrations (mg/l) of 15 on day 1, 2.8 at 7-10 d and 2.6 by
