Practicalities of Glutathione Supplementation in Nutritional Support
Current Opinion In Clinical Nutrition And Metabolic Care 2002;5:321-326.
Erick Valencia; Gil Hardy.

Oral Glutathione (GSH) appears to be efficiently absorbed in rats [2,3], however, the same may not necessarily be true for GSH supplements in humans. For example, when seven healthy subjects were given a single oral dose of up to 3 g of GSH, there was no increase in blood GSH levels [4], the authors of the study concluded "it is not feasible to increase circulating GSH to a clinically beneficial extent by the oral administration of a single dose of 3000 mg of GSH." Absorption of GSH may be better in rats because the human gastrointestinal tract contains significant amounts of an enzyme -glutamyltranspeptidase that breaks down GSH [1 ]. Very preliminary evidence has suggested that absorption of GSH can occur in the mouth when GSH tablets are placed between the teeth and the inner cheek [5]. Although there have been several anecdotal reports on the possibility that oral administration of GSH may have beneficial effects against specific disease processes, relatively few scientific studies have been published.

References:

1. Valencia E, Marin A, Hardy G. Glutathione-nutritional and pharmacologic viewpoints: Part IV. Nutrition 2001; 17: 783-784.
   wThis is a comprehensive review of GSH in foods and its gastrointestinal absorption.
2. Hagen TM, Wierzbicka TG, Sillau AH, et al. Fate of dietary glutathione: disposition in the gastrointestinal tract. Am J Physiol 1990; 259: G524-G529.
3. Favilli F, Marraccini P, Lantomasis T, Vincenzini MT. Effect of orally administered glutathione on glutathione levels in some organs of rats: role of specific transporters. Br J Nutr 1997; 78: 293-300.
4. Witschi A, Reddy S, Stofer B, Lauterburg BH. The systemic availability of oral glutathione. Eur J Clin Pharmacol 1992; 43 (6): 667-669.
5. Hunjan MK, Evered DF. Absorption of glutathione from the gastrointestinal tract. Biochim Biophys Acta 1985; 815: 184-188.