The uniqueness of undenatured whey protein isolate Immunocal is that it delivers the crucial precursor cysteine into the cell in the form ready for glutathione production directly in the cell. Immunocal is clinically proven to raise AND maintain optimal glutathione levels in serum and tissue. It is made from milk and is as safe as food can be. Immunocal's effectiveness is backed by extensive medical research and clinical trials.
It has been shown that taking cysteine (L-cysteine) as a supplement may in fact raise glutathione to some degree. But synthetic cysteine taken this way is potentially toxic. Cysteine toxicity leads to a number of disorders in the body, from heart disease to renal (kidney) disease. Due to the potential for cysteine toxicity, excessive homocysteine and hypercysteinemia, it is not recommended to take L-cysteine supplements without strict supervision from your physician.
Oral glutathione is useless in raising plasma and tissue glutathione levels as most of it gets broken down in the digestive system and does not reach cells. Only very small amounts of glutathione make it into the bloodstream. One study showed an increase in plasma GSH after administering dietary glutathione to rats with chemically inhibited glutathione synthesis. However, no increase in liver was observed where it is most needed since liver is the largest and most important detoxifying organ. Researchers have proved that the bioavailability (usefulness) of oral glutathione is very low, and in this form it cannot seriously affect immune health.
NAC – N-acetyl-cysteine - is a potent glutathione precursor that has been available as a pharmaceutical drug and also can be found on the shelves of health supplement stores in less potent doses. Many people eating NAC report rash, wheezing, nausea, vomiting, cramps and diarrhea. NAC is widely used in hospital emergency rooms on patients suffering from severe acetaminophen toxicity due to overdose in order to quickly boost their glutathione levels and save their lives. These measures often lead to above-mentioned side effects. Also, raising glutathione levels with NAC has only temporary effect that lasts only several hours after which glutathione levels drop, sometimes below the original level. My advice is to stay away from NAC supplements.