Long-term stability of blood glutathione and cysteine in humans.

Glutathione (GSH) availability is an important factor in the maintenance of health. Accordingly, blood GSH has been proposed as an indicator of health status. To validate the use of blood GSH in population studies, we investigated the long-term intraindividual variation of blood GSH and cyst(e)ine (Cys and cystine) concentrations in healthy adults. In a longitudinal study of 10 subjects, GSH and cyst(e)ine were measured in blood samples collected weekly over 8 months. The average within-person CV for GSH was only 9.1% compared with an observed interindividual CV of 20%. Blood cyst(e)ine was more variable within individuals (mean CV 14.7%) than GSH, whereas the interindividual CV for cyst(e)ine was lower (8.6%). The results demonstrate the stability of blood GSH in free-living subjects and the utility of GSH measurements as an indicator of long-term GSH status.