Abstract The in vivo effects of drinking a water product, which had been confirmed to have antioxidant activities in vitro, were preliminarily studied by monitoring the blood concentrations of oxidative stress marker substances in the two group subjects who ingested the same quantity of the water product and a tap water solution during the same time. The results indicated that hydrogen gas and reductive vanadium ions as the components responsible for the antioxidant activities in vitro cannot enhance the scavenging ability for reactive oxygen species in vivo after being drunk and absorbed into the human body, although it was suggested that an ingestion of a greater quantity of water than usual gives a slight reduction, overall, in the oxidative stress. (Author abst.)
