Amino Acid
L-Cystine
Also known as: Cystine, L-Cystine
B
Evidence
Oxidized dimer form of cysteine, important for keratin production, hair/nail/skin health, and antioxidant support via glutathione synthesis.
Primary uses
- Hair health
- Nail strength
- Skin support
- Keratin synthesis
- Glutathione precursor
How it works
- Reduced to cysteine in the body
- Provides sulfur for keratin production
- Supports glutathione synthesis
- Structural component of hair and nails
Dosage
- Typical range
- 500-1500 mg daily
- Timing
- With meals
- With food
- Best with food
- Duration
- Safe long-term
- Special populations
- Hair/nail support
Forms
- Capsule
- Powder
Safety
Common side effects
- Well tolerated
Contraindications
- Cystinuria
Evidence notes
Established role in keratin synthesis and sulfur metabolism
Grade B: Some human trials support key claims; further confirmation needed.
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