There is weak evidence of diuresis and proteinuria after high dose molybdenum intake in animals (Bompart et al., 1990). Asmangulyan (1965) evaluated the effects of molybdenum in rabbits receiving four different oral doses (0.025, 0.5, 5, and 50 mg/kg/day) for 6 months. At a dose of 5 mg/kg/day, histological changes were observed in kidney and liver along with body weight loss. No effects were observed at lower molybdenum dosage levels.

Increased Uric Acid in Plasma and Urine. Key human studies on this endpoint include Chappell and coworkers (1979), Deosthale and Gopalan (1974), and Kovalsky and coworkers (1961). Kovalsky and coworkers (1961) observed hyperuricemia and arthralgias in Armenians who consumed 10 to 15 mg/day of molybdenum from food. Serum molybdenum concentration was positively correlated with serum uric acid concentration. Elevations in blood molybdenum concentrations were accompanied by decreases in blood copper concentrations. However, serious methodological difficulties are noted with this particular study including possible analytical problems in the assessment of blood and urinary copper levels and the very small size of the control group in contrast to the molybdenum-exposed group.

Other studies in humans do not support the existence of this particular adverse manifestation in association with elevated dietary intakes of molybdenum. For example, Chappell and coworkers (1979) reported reduced uric acid concentrations in serum after molybdenum intakes of greater than 7 μg/kg/day from drinking water. Deosthale and Gopalan (1974) reported no change in uric acid excretion at intakes up to 1.5 mg/day in four volunteers.

Impaired Copper Utilization. Impaired utilization of copper has been observed in ruminants (Mills and Davis, 1987) and is based on an interaction between molybdenum, copper, and sulfur that occurs in ruminants but not in humans. A human study involving doses up to 1.5 mg/day showed no adverse effects on copper utilization (Turnlund and Keyes, 2000).

Reproductive Effects. The administration of supplemental dietary molybdenum was associated with a prolonged estrus cycle, decreased gestational weight gain of the pups, and several adverse effects on embryogenesis in female Sprague-Dawley rats (Fungwe et al., 1990). These effects were not observed at 0.9 mg/kg/day, but were observed at doses of 1.6 mg/kg/day (based on a gestational weight of 100 g). Schroeder and Mitchener (1971) evaluated the effect of