Background：Glutathione (GSH) is produced in every cell in the body, where it acts as an antioxidant to neutralize free radicals and prevent oxidative cellular damage. Alterations in GSH levels are reported in neurological, inflammatory diseases as well as immune dysfunction. Several studies in animals and humans involving supplementation with whey protein or whey protein isolates from milk have documented increases in plasma and tissue glutathione concentrations along with reductions in oxidative stress, while the effects of casein on GSH are as yet not clear. One of the major components of the casein family is beta-casein and evolutionarily there are two major type of beta-casein: A1 and A2. The presence of histidine at position 67 allows a protein fragment of seven amino acids, known as beta-casomorphin-7 (BCM-7), to be produced on enzymatic digestion only from A1 but not from A2 beta-casein. BCM7 is an opioid peptide and can act on mu-opioid receptor similar to morphine. We have previously reported that BCM-7 can reduce cysteine uptake in cultured human neuronal and gastrointestinal epithelial cells by activating opioid receptors, inducing oxidative stress by decreasing the levels of GSH.