GGT
Gamma-glutamyl transferase — a liver and bile duct enzyme that also reflects oxidative stress.
Optimal Range
< 25 U/L (optimal) · < 50 U/L (lab range)
Risk-Stratified Targets
| Population / Context | Target |
|---|---|
| Optimal (low oxidative stress) | < 25 U/L |
| Normal lab range | < 50 U/L (men) · < 32 U/L (women) |
| Mildly elevatedInvestigate metabolic syndrome, alcohol, medications | 50–100 U/L |
| Significantly elevatedConsider bile duct obstruction, chronic liver disease | > 100 U/L |
Why It Matters
GGT is a marker of oxidative stress and glutathione depletion beyond just liver health. Elevated GGT independently predicts cardiovascular disease, diabetes, and all-cause mortality.
Understanding GGT
GGT (gamma-glutamyl transferase) is an enzyme found on the surface of liver cells, bile duct cells, and several other tissues. While traditionally viewed as a marker of liver and bile duct disease (and alcohol consumption), research over the past two decades has revealed GGT to be a far more powerful biomarker than previously appreciated — it independently predicts cardiovascular disease, diabetes, metabolic syndrome, and all-cause mortality.
The key insight is that GGT plays a central role in glutathione metabolism. Glutathione is the body's most important intracellular antioxidant, and GGT is involved in breaking down extracellular glutathione to recycle its amino acid components for intracellular glutathione synthesis. Elevated GGT reflects increased oxidative stress and glutathione demand — a state that drives aging and chronic disease at the cellular level.
In practical terms, GGT elevation should prompt investigation beyond liver disease. While alcohol use and bile duct obstruction are classic causes, metabolic syndrome, NAFLD, oxidative stress from environmental toxins, and even chronic medication use can elevate GGT. A GGT below 25 U/L is a strong signal of low oxidative stress and good metabolic health. Like ALT, GGT responds well to lifestyle interventions — particularly reduced alcohol, weight loss, and increased intake of cruciferous vegetables (which support glutathione production).
Key Research
Gamma glutamyltransferase and risk of future dementia in middle-aged to older Finnish men
Kunutsor SK et al. · Alzheimers Dement (2015)
Key finding: Elevated GGT was independently associated with increased risk of dementia, supporting its role as a marker of oxidative stress and systemic inflammation beyond liver disease.