Glutathione

Glutathione is an endogenous tripeptide (cysteine + glutamate + glycine) that the body synthesises inside its cells. It is the main intracellular antioxidant, takes part in phase II hepatic detoxification and modulates immunity. Its oral bioavailability was debated for decades, but recent clinical trials show that sufficient doses raise tissue levels. This page covers its function, supplementation forms, studied doses and precursors.

What is glutathione?

Glutathione (γ-L-glutamyl-L-cysteinyl-glycine, abbreviated GSH for glutathione in its reduced form) is an endogenous tripeptide present at millimolar concentrations inside cells. It is the most abundant non-enzymatic antioxidant in the cellular cytoplasm and takes part in hundreds of biochemical reactions. Its synthesis occurs in two consecutive enzymatic steps: γ-glutamylcysteine synthetase joins glutamate and cysteine, and glutathione synthetase adds the glycine residue. Cysteine is the limiting amino acid because its plasma reserves are the lowest of the three precursors.

Chemical composition and redox forms: GSH ↔ GSSG

Glutathione exists in two interconvertible forms: the reduced form (GSH), functional as an antioxidant, and the oxidised form (GSSG), which is a dimer formed by two GSH molecules joined by a disulphide bridge. The GSH:GSSG ratio in a healthy cell is around 100:1, and this ratio is used as a biomarker of cellular redox status. When oxidative stress increases, the ratio falls because glutathione is oxidised faster than it is regenerated. The enzyme glutathione reductase, aided by the cofactor NADPH, recovers GSSG to GSH and maintains the cycle.

Endogenous synthesis and amino acid precursors

The body produces glutathione continuously from glutamate, cysteine and glycine. The three amino acids are available in a normal diet with sufficient protein, but cysteine is the most sensitive to deficiencies because its free form is chemically unstable. For this reason, supplementation with N-acetylcysteine (NAC) is a widely researched strategy to raise endogenous synthesis: NAC delivers cysteine to cells without the limitations of the free amino acid. Other studied precursors include cystine, methionine and L-2-oxothiazolidine-4-carboxylate.

For a more detailed review of NAC as a glutathione precursor, see the N-acetylcysteine (NAC) page.

Mechanism of action: how glutathione works at the cellular level

Glutathione exerts its biological activity through several simultaneous mechanisms that distinguish it from other antioxidants.

The GSH/GSSG redox cycle

Glutathione's direct antioxidant function consists of donating an electron to reactive oxygen species (ROS) such as hydrogen peroxide, the hydroxyl radical or lipid hydroperoxides. On donating the electron, two GSH molecules join to form GSSG. Subsequently, the enzyme glutathione reductase, using NADPH as an electron donor, reduces GSSG to 2 GSH and restarts the cycle. This system allows glutathione to function as a regenerative system that is not depleted as long as the NADPH supply is adequate.

Glutathione peroxidase and dependent enzymes

Glutathione acts as an essential substrate for several enzyme families. Glutathione peroxidase (GPx), a selenoprotein, neutralises hydrogen peroxide and lipid hydroperoxides using GSH as a cofactor — this enzyme is one of the main defence systems against oxidative damage in cell membranes. The glutathione-S-transferases (GST) catalyse the conjugation of glutathione with xenobiotics, endogenous electrophiles and reactive metabolites, marking them for excretion. The glutaredoxins take part in protein regulation through reversible glutathionylation.

Hepatic detoxification (phase II)

The liver uses glutathione in phase II of xenobiotic metabolism: many potentially toxic compounds generated by phase I (cytochrome P450) are conjugated with GSH before their urinary or biliary elimination. For this reason, hepatic glutathione concentrations are particularly high and its depletion is associated with hepatotoxicity — the paradigmatic case is paracetamol poisoning, where the depletion of hepatic glutathione is the central mechanism of damage and intravenous N-acetylcysteine is the standard antidote precisely because it restores the substrate for GSH synthesis.

Benefits of glutathione according to clinical evidence

Informational note: The information in this section is for educational purposes and is based on published scientific research. It does not constitute medical advice or a therapeutic recommendation. Always consult your doctor or pharmacist before starting any supplementation, especially if you have a health condition or take medication.

Clinical research on glutathione has concentrated on several areas. The evidence is heterogeneous depending on the outcome studied, the form used and the population.

Oxidative stress and antioxidant capacity

This is the area with the most consistent evidence. Clinical trials that have supplemented glutathione orally in its different formulations have reproducibly shown increases in markers of antioxidant capacity in blood and reductions in markers of oxidative damage such as 8-isoprostane and lipid peroxidation products. The magnitude of the effect depends on the dose, the duration and the formulation used. Translating these biochemical changes into sustained clinical benefits in healthy people requires longer trials with defined clinical endpoints.

Immune function

Glutathione modulates the function of several components of the immune system, including T lymphocytes, dendritic cells and macrophages. Intracellular GSH concentrations influence Th1/Th2 differentiation and the cytotoxic capacity of natural killer cells. Small studies have documented increases in markers of immune function — lymphocyte proliferation, NK activity — after supplementation with liposomal glutathione. The samples are limited and the findings require confirmation with larger studies before they can be translated into general recommendations.

Liver and detoxification

The therapeutic use of intravenous N-acetylcysteine as an antidote in paracetamol poisoning is the most solid clinical evidence of glutathione's role in hepatic protection. In the context of oral supplementation in people without liver pathology, the evidence is much more limited and the results are heterogeneous. Claims of the "detoxifies the liver" type lack support in the peer-reviewed scientific literature.

Supplementation forms: oral, liposomal and intravenous

The oral bioavailability of glutathione has been the subject of scientific debate for decades. The evidence has evolved in recent years with the publication of clinical trials designed to answer this question specifically.

Oral GSH: the bioavailability debate

The classic objection to oral glutathione was that intestinal peptidases hydrolyse it into its constituent amino acids before it can be absorbed intact, so supplementation would be equivalent to providing cysteine, glutamate and glycine. A 6-month randomised, double-blind, placebo-controlled clinical trial in 54 non-smoking adults challenged this view: participants who received 1,000 mg/day of oral glutathione significantly raised their GSH levels in erythrocytes (≈30%), plasma (≈30%) and buccal mucosa cells (≈260%). The 250 mg/day group also showed increases, although smaller. The effects were dose- and time-dependent and reverted after a one-month washout.

Liposomal glutathione

Liposomal formulations encapsulate glutathione in lipid vesicles with the aim of protecting it from digestive degradation and improving absorption. A pilot clinical trial in 12 healthy adults that compared doses of 500 and 1,000 mg/day over 4 weeks documented increases in GSH in whole blood of up to 40%, in erythrocytes of 25%, in plasma of 28% and in peripheral blood mononuclear cells of 100%, together with reductions in the oxidative stress marker 8-isoprostane and improvements in markers of immune function. The sample is limited and the heterogeneity between commercial liposomal formulations means that these results are not automatically extrapolable to any product on the market.

Intravenous glutathione (medical use)

Important note: The intravenous administration of glutathione is a medical act that requires prescription and professional supervision. The information about this route is included for purely educational purposes to contextualise the evidence. It does not constitute a recommendation for use and cannot be replaced by oral supplementation.

Intravenous administration bypasses the digestive barrier and allows high plasma concentrations to be reached. It has been investigated in specific clinical contexts such as Parkinson's disease, cystic fibrosis and cisplatin chemotherapy. The clinical results have been heterogeneous and the protocols vary between studies. The oral and intravenous routes are not interchangeable: what the evidence documents for one does not carry over to the other.

Dietary sources and precursors

Glutathione is present in a variety of foods, although the amounts are modest in terms of the doses investigated in supplementation. More important than the direct intake is the supply of the amino acid precursors that sustain endogenous synthesis.

Foods rich in glutathione

• Fresh vegetables: asparagus, spinach, broccoli, kale, avocado, cucumber and tomato provide significant amounts in their reduced form when eaten raw or lightly cooked. Prolonged cooking degrades GSH.
• Fruit: watermelon, strawberries, peach, papaya and orange contain GSH in smaller but relevant amounts.
• Meat and fish: animal muscle contains glutathione, especially fresh offal. Industrial processing significantly reduces the content.
• Unprocessed dairy products: they contain glutathione, especially the unpasteurised versions, although their consumption in this format is not recommended due to microbiological risk.

Amino acid precursors

Rather than the direct intake of glutathione, what is physiologically relevant is having the amino acids needed to synthesise it available. Cysteine is the limiting factor. The usual dietary sources of cysteine and its precursor methionine include eggs, dairy products, meat, fish, legumes, whole grains and nuts. Supplements based on N-acetylcysteine and, to a lesser extent, on free L-cysteine, are strategies studied to raise the cellular availability of cysteine and, with it, the endogenous synthesis of glutathione.

Doses studied in clinical trials

The doses used in the published clinical trials vary according to the form and the objective of the study. The documented ranges are set out below for informational purposes.

Table of oral doses documented in clinical research

Intravenous route (supervised medical use): hospital protocols for Parkinson's disease, cystic fibrosis and other clinical contexts have used doses between 600 and 1,400 mg administered several times per week. This route is not comparable to oral supplementation.

Considerations on oral bioavailability: there is significant inter-individual variability in the response to oral supplementation. Factors such as baseline nutritional status, age and the presence of polymorphisms in synthesis enzymes (γ-glutamylcysteine synthetase) may modulate the magnitude of the effect. Taking it on an empty stomach appears to favour absorption.

Important note: The doses mentioned correspond to those used in clinical research. They do not constitute a dose recommendation. Consult your doctor or pharmacist before starting any supplementation.

Safety, side effects and interactions

Glutathione presents a favourable safety profile within the dose ranges investigated as a food supplement. As with any bioactive compound, its consumption is not free of considerations.

Adverse effects

At the usual oral supplementation doses (250-1,000 mg/day), the adverse effects reported are scarce and mild in nature. The most frequent include occasional gastrointestinal discomfort (nausea, bloating, occasional diarrhoea), mild alterations of body odour or breath due to sulphur compounds, and rare skin reactions. The incidence remained similar to placebo in the published clinical trials.

Contraindications and special populations

• Pregnancy and breastfeeding: the safety data are insufficient to recommend supplementation. It is advised against except on express medical indication.
• Children and adolescents: there are insufficient data to establish safe doses in these populations.
• Asthma: there is debate about the safety of supplementation with sulphur compounds in people with sulphite-sensitive asthma. Consult a specialist.
• Organ transplant or immunosuppressive therapy: consult the treating doctor; glutathione modulates immune function and the interaction is not well characterised.

Relevant drug interactions

• Chemotherapy (cisplatin and derivatives): glutathione may modulate the toxicity and efficacy of some chemotherapeutic agents. People undergoing oncological treatment should consult their oncologist before any supplementation.
• Anticoagulants and antiplatelet agents: no relevant drug interactions have been documented at the usual doses, but it is recommended to always inform the doctor.

How to choose a glutathione supplement

The glutathione supplement market is heterogeneous. The following technical criteria help to evaluate a product with judgement:

• Chemical form: check whether the product contains reduced glutathione (GSH) or a liposomal formulation. Authentic liposomal formulations (not simple mixtures with lecithin) usually indicate the encapsulation method.
• Dose per serving: clinical trials have typically used 500-1,000 mg/day. Significantly lower doses may offer marginal or no benefits.
• Origin of the glutathione: the glutathione used in supplements usually comes from fermentation with strains of Saccharomyces cerevisiae (yeast). This biotechnological origin offers superior purity and traceability to the chemically synthesised one.
• Formulated synergies: products that combine GSH with its precursors (NAC, cysteine) or cofactors such as selenium (substrate of glutathione peroxidase) may enhance the systemic effect on the redox balance.
• Absence of unnecessary additives: avoid formulations with titanium dioxide, excess magnesium stearate, artificial colourings or an excess of excipients.
• Traceability and certifications: the manufacturer should offer batch traceability, certificates of analysis and, ideally, GMP certifications.

Glutathione in the Pleniage portfolio

In the PLENIAGE® ANTIOX PRO formulation, glutathione (120 mg) is incorporated together with its most studied precursor, N-acetylcysteine (300 mg). This combination responds to a documented biochemical rationale: providing simultaneously preformed glutathione and the cysteine needed to sustain endogenous synthesis. The product also includes other components of the antioxidant system (CoQ10, turmeric, pomegranate, astaxanthin, lutein and lycopene) that act in different cellular compartments.

This page is part of the Antioxidants and defences cluster, where the molecules involved in cellular redox balance are explored in an integrated way. To go deeper into the most relevant precursor, see the N-acetylcysteine (NAC) page.

Frequently asked questions about glutathione

What exactly is glutathione and what is it for?

Glutathione is a tripeptide (formed by three amino acids: glutamate, cysteine and glycine) that the body synthesises inside its cells. It functions as the most abundant intracellular antioxidant, takes part in phase II hepatic detoxification and is a cofactor of several key enzymes of the endogenous antioxidant system, such as glutathione peroxidase.

Does glutathione work orally or is it destroyed in digestion?

The classic objection to oral glutathione was its intestinal hydrolysis. Clinical trials published since 2015, with doses of 250-1,000 mg/day, have documented significant increases of GSH in blood and tissues after sustained oral supplementation (weeks or months). The effect is dose-dependent and reversible upon stopping intake.

Is liposomal glutathione better than the normal reduced one?

Liposomal glutathione is designed to protect the molecule from digestive degradation. The small studies available show increases of GSH and improvements in antioxidant markers at doses similar to those of non-liposomal GSH. The heterogeneity between market formulations makes a universal comparison difficult: the quality of the liposome matters as much as the declared dose.

What is the relationship between N-acetylcysteine and glutathione?

N-acetylcysteine (NAC) is a precursor of glutathione: it provides the cysteine needed for endogenous synthesis. NAC has a long history of clinical use, especially as an antidote in paracetamol poisoning and as a mucolytic medication. Combining both compounds is a common formulation strategy.

Does glutathione have any health claim approved by EFSA?

At present, glutathione does not have health claims approved by the European Food Safety Authority (EFSA) under Regulation (EC) 1924/2006. This means that manufacturers cannot attribute disease prevention or treatment properties to it on the label. Scientific research documents effects on biochemical markers, but the regulatory approval of claims requires a specific level of evidence that glutathione, to date, has not formally reached.

Which foods provide the most glutathione?

Asparagus, spinach, broccoli, avocado, watermelon and strawberries contain the largest amounts in their reduced form. Prolonged cooking degrades glutathione, so consuming it raw or lightly cooked better preserves the content. More relevant than the direct intake is having the precursor amino acids (cysteine, glutamate, glycine) available through a diet with quality protein.

Glutathione is one of the most studied components of the endogenous antioxidant machinery. The clinical evidence consistently documents that oral supplementation, in sufficient doses and in a sustained way, raises tissue GSH concentrations and improves biochemical markers of redox status. Translating these biochemical changes into broad clinical benefits in healthy people requires longer trials with defined clinical endpoints. If you are interested in going deeper into strategies to sustain cellular redox balance, consult your doctor or pharmacist to assess whether supplementation is appropriate for your personal situation.

At PLENIAGE® we publish scientific content on evidence-based supplementation. You can explore the Antioxidants and defences cluster for more pages and related articles.

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References

The statements in the article are based on available scientific literature. The key verified references that support the main claims of the page are listed below.

• Wu G, Fang YZ, Yang S, Lupton JR, Turner ND. Glutathione metabolism and its implications for health. J Nutr. 2004;134(3):489-92. PMID: 14988435.
• Perricone C, De Carolis C, Perricone R. Glutathione: a key player in autoimmunity. Autoimmun Rev. 2009;8(8):697-701. PMID: 19393193.
• Morris D, Khurasany M, Nguyen T, et al. Glutathione and infection. Biochim Biophys Acta. 2013;1830(5):3329-49. PMID: 23089304.
• Richie JP Jr, Nichenametla S, Neidig W, et al. Randomized controlled trial of oral glutathione supplementation on body stores of glutathione. Eur J Nutr. 2015;54(2):251-63. PMID: 24791752.
• Sinha R, Sinha I, Calcagnotto A, et al. Oral supplementation with liposomal glutathione elevates body stores of glutathione and markers of immune function. Eur J Clin Nutr. 2018;72(1):105-111. PMID: 28853742.
• Murphy MP. How mitochondria produce reactive oxygen species. Biochem J. 2009;417(1):1-13. PMID: 19061483.