Effect of prolonged supplementation with daily supplements of selenomethionine and sodium selenite on glutathione peroxidase activity in blood of New Zealand residents.

Glutathione peroxidase (EC 1.11.1.9, GSH-Px) activities and selenium (Se) concentrations in blood of 12 New Zealand residents were followed during prolonged supplementation with physiological doses (100 microgram Se) of sodium selenite (selenite-Se) or selenomethionine (Semet-Se). GSH-Px activities increased in all subjects but at 17 wk the mean increase was not significantly greater for Semet-Se (6.2 +/- SD 3.2 units/g Hb) than for selenite-Se (3.7 +/- 1.8 units/g Hb). After dosing ceased, GSH-Px activities for most subjects returned to predosing values in 17 to 40 wk, but in some subjects activities remained high. Increases in Se concentrations in whole blood, erythrocytes, and plasma were greater after Semet-Se than after selenite-se. Se concentrations tended to plateau after selenite-Se while after Semet-Se they continued to rise as long as dosing continued. Enzyme activity of one of four subjects supplemented daily with 500 microgram selenite-Se was unchanged, despite a great increase in plasma Se. Blood Se and GSH-Px of 23 New Zealand residents who ingest regular large doses (0.5 to 3 mg Se) mainly of selenite-Se showed that those who dosed weekly had greater values than the less frequent dosers. Three subjects showed extremely high values. It is suggested that each individual might have an optimal level of GSH-Px activity, so that the level reached is a balance between Se intake and other factors, including possible stressor effect of selenite.