dietary supplement for 5 days were 27 nmol/L (1.48 μg/L), whereas unsupplemented control subjects had a mean serum concentration of 20 nmol/L (1.1 μg/L).

Serum or plasma manganese concentrations appear to be somewhat sensitive to large variations in manganese intake, but longer studies are needed to evaluate the usefulness of serum manganese concentrations as indicators of manganese status.

An advantage of whole blood manganese concentration over plasma or serum manganese concentration as an indicator is that slight hemolysis of samples can markedly increase plasma or serum manganese concentrations. Whole blood manganese seems to be extremely variable, however, which may preclude it as a viable status indicator. In a manganese depletion study, manganese concentration in whole blood was 9.57 μg/L (range 5.40 to 17.1) at the end of the baseline period and 6.01 μg/L (4.43 to 7.57) at the end of the 39-day depletion period, but there was not a significant difference between these values (Friedman et al., 1987). With 10 days of manganese repletion, whole blood manganese concentration increased to 6.99 μg/L (3.93 to 18.3).

Urinary manganese is responsive to severe manganese depletion. After a patient spent 7 days on a depletion diet containing 0.11 mg/ day of manganese, the patient’s urinary manganese excretion significantly decreased from 8.64 to 2.45 μg/day, and it continued to decrease to as low as 0.39 μg/day after 35 days (Friedman et al., 1987). In a second manganese depletion trial, urinary manganese decreased significantly as manganese intake decreased from 2.9 to 2.1 to 1.2 mg/day (Freeland-Graves et al., 1988). After repletion with 3.8 mg/day, urinary manganese excretion increased then decreased following an intake of 2.65 mg/day.

In contrast to the above findings, when ten men consumed 0.52 to 5.33 mg/day, urinary excretion of manganese did not correspond with manganese intake (Greger et al., 1990). Urinary losses of manganese averaged 0.38 μg/g creatinine. Also, Davis and Greger (1992) could not demonstrate that women given 15 mg/day of manganese during a 125-day supplementation period excreted more manganese in urine than women consuming 1.7 mg/day in food. Thus, there is controversy on the use of urinary manganese for