N-acetylcysteine (NAC)
Cysteine source that cells use to make glutathione, the antioxidant that declines with age.
Summary
Debbie presents NAC as a way to supply cysteine, one of the two limiting amino acids (with glycine) for glutathione, which falls with age as oxidative stress rises. She emphasizes that glycine and cysteine together, rather than either alone, restored glutathione in older adults and improved several aging measures in a 6-month trial. NAC was also one of four 'combined metabolic activators' in a positive phase II Alzheimer's trial, and animal and cell studies suggest it protects the brain against oxidative stress and amyloid-beta.
She fills her own gelatin capsules with NAC because "There's no disguising the taste of NAC."From Longevity Supplements: How Many Capsules Are You Swallowing?
The evidence
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Human trial
A randomized, placebo-controlled phase II trial in 69 Alzheimer's patients using a combination that included 2.55 g NAC (with L-serine, NR and L-carnitine) improved ADAS-Cog scores by day 84.
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Human trial
In a 6-month clinical trial in adults aged 70+, glycine plus NAC corrected glutathione deficiency and improved inflammation, insulin resistance, cognition, strength, walking speed and exercise capacity.
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Human trial
In elderly adults, supplementing glycine and cysteine raised glutathione by 94.6% within two weeks, back to levels seen in younger people.
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Human trial
In older adults with HIV, two weeks of cysteine plus glycine corrected glutathione deficiency and improved mitochondrial function.
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Animal
In very old mice, glycine plus NAC reversed cognitive decline, pointing to mitochondrial dysfunction and oxidative stress as root causes.
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Animal
In mouse Alzheimer's studies NAC raised brain glutathione and improved learning and memory; in brain cell cultures it protected against amyloid-beta and neuron death.
Doses used in studies
Amounts reported in the research, not dosing recommendations.
| Dose | Context |
|---|---|
| 0.81 mmol/kg/day (about 8 g/day for a 130 lb person, split into two doses) | 6-month glycine + NAC trial in adults aged 70+ |
| 2.55 g once daily for 28 days, then twice daily for two months | Combined metabolic activator phase II Alzheimer's trial |
Cautions
- NAC may interact with medications such as nitroglycerine and can lower blood pressure, a concern for people already on blood pressure medication.
- She notes the trial dose seems really high for NAC, though that trial ran for 6 months.
- Check drug interactions and talk with your doctor or pharmacist if you take medications; NAC powder has a strong sulfur-like aftertaste.