Molybdenum

BACKGROUND

Molybdenum acts as a cofactor for the enzymes sulphite oxidase, xanthine oxidase and aldehyde oxidase. These enzymes are involved in catabolism of sulphur amino acids and heterocyclic compounds including purines and pyridines. No clear deficiency syndrome has been seen in animals even with major reductions in molybdoenzymes. Molybdenum is absorbed very efficiently over a wide range of intakes by passive transport and urinary excretion reflects intake (Turnlund et al 1995a,b).

Molybdenum is found in plant foods and reflects the soil content in which they grow. Legumes are major contributors of molybdenum in the western diet, as are grain products and nuts (Pennington & Jones 1987, Tsongas et al 1980). Animal foods, fruits and vegetables are low in molybdenum. Little is known about bioavailability from various foods. There are no data for Australia or New Zealand either for dietary or supplemental intake. One US study reports dietary intakes from 120–240 µg/day, averaging 180 µg/day (Tsongas et al 1980). The US Total Diet study showed dietary intakes of 76 µg/day for women and 109 µg/day men (Pennington & Jones 1987).

Deficiency has not been seen in otherwise healthy people. Evidence of essentiality relates to a specific genetic defect that prevents the synthesis of sulphite oxidase and can lead to severe neurological damage and to the demonstration of amino acid intolerance in a long-term parenterally fed patient where molybdenum was omitted from the feed (Abrumrad et al 1981, Johnson 1993). There is some limited and inconclusive epidemiological data that low intakes may be associated with increased incidence of oesophageal cancer (WHO 1996).

Plasma, serum or urinary concentrations of molybdenum or indicators can be used to assess requirements, as plasma levels are generally low and difficult to measure, and urinary measures alone do not reflect status. Molybdenum balance studies are therefore used to establish homeostasis and changes in body stores. Two such studies have been done in men (Turnlund et al 1995a,b), and one in pre-adolescent girls (Engel et al 1967).