An open-label dose-response study of lymphocyte glutathione levels in healthy men and women receiving pressurized whey protein isolate supplements.

Background: High-pressure treatment of whey protein may increase digestibility and bioavailability of cysteine. The purpose of the study was to determine whether total lymphocyte glutathione (gamma-glutamyl-cysteinyl-glycine [GSH]) levels (oxidized+reduced) can be augmented from three different doses of pressurized whey protein supplements in a dose-dependent manner over a 2-week period.

Methods: Eighteen healthy males and 18 healthy females were randomized into three different groups, with 31 finishing the study. Each group ingested 15, 30, or 45 g/day pressurized whey protein in the morning in bar format for 14 days. Each group was blinded to the amount of whey protein they were ingesting. Ten millilitres of blood was withdrawn before and after the 2-week period to assess blood lymphocyte levels pre and post supplementation.

Results: There was no change in body weight or reported physical activity levels pre and post supplementation. Pre-lymphocyte GSH levels were not significantly different between groups (3.7+/-0.7 micromol/l). Least-squares linear regression showed that the change in lymphocyte GSH levels from pre to post supplementation was affected by the amount of whey protein ingested daily (P=0.037). The group that ingested 45 g/day pressurized whey protein augmented GSH levels the most (by approximately 24%), and the group that ingested 15 g/day did not increase lymphocyte GSH levels.

Conclusions: We conclude that there is a significant relationship between the dosage of supplementation and the change in lymphocyte GSH levels. Furthermore, the increase in GSH was linear with the amount of whey protein ingested. Pressurized whey protein supplementation of 45 g/day for 2 weeks can increase lymphocyte GSH by 24%.