Supplement
L-cysteine is an amino acid the body uses to build proteins such as keratin and to make glutathione, one of its main internal antioxidants. People mostly look at it for antioxidant status, and a few small human studies found it protected against oxidative stress from hard exercise, including less DNA oxidation and better-preserved red blood cell enzyme activity. Still, the evidence is limited, since only about 60 people took part in total, and the alcohol and hair findings come mostly from animal work.
Sources: PMID 16517176; PMID 16959232; PMID 17243918
- Updated
- How we grade
- 8 studies cited
- Best evidence
- Grade C
- Conditions studied
- 3
- Outcomes
- 5
- Graded outcomes
- 0023
Evidence by condition
- Strong
- Moderate
- Limited
- Very limited
| Grade | Outcome | Effect | Size | Studies | People | Studies list |
|---|---|---|---|---|---|---|
| Antioxidant Status Multiple human studies found that L-cysteine supplementation protected against exercise-induced oxidative stress, preventing DNA oxidation, preserving erythrocyte G6PD activity, and maintaining erythrocyte membrane ATPase activities during forced training. | Improves (the measure goes up) | Moderate effect | 3 studies | 60 people | ||
Studies that measured antioxidant status
| ||||||
| Grade | Outcome | Effect | Size | Studies | People | Studies list |
|---|---|---|---|---|---|---|
| Erythrocyte Membrane Integrity Human studies showed L-cysteine supplementation preserved erythrocyte membrane acetylcholinesterase and Na+,K+-ATPase activities and protected G6PD activity from reduction during exercise-induced oxidative stress. | Improves (the measure goes up) | Small effect | 2 studies | 40 people | ||
Studies that measured erythrocyte membrane integrity | ||||||
Alcohol Use Disorder
- Alcohol-Induced Oxidative Damage: improves
| Grade | Outcome | Effect | Size | Studies | People | Studies list |
|---|---|---|---|---|---|---|
| Alcohol-Induced Oxidative Damage In rodent models, L-cysteine (often combined with ascorbate and L-methionine) reduced alcohol-induced oxidative stress in the brain, stomach, testes, ovary, kidney, and lung of chronically alcohol-treated rats. | Improves (the measure goes down) | Moderate effect | 3 studies | |||
Studies that measured alcohol-induced oxidative damage
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General
- Skin Pigmentation: changes; see studies
- Hair and Nail Health: improves
| Grade | Outcome | Effect | Size | Studies | People | Studies list |
|---|---|---|---|---|---|---|
| Skin Pigmentation A single study found that simultaneous administration of vitamin C, L-cysteine, and vitamin E inhibited melanogenesis, suggesting a potential skin-lightening effect, though the contribution of L-cysteine alone is difficult to isolate from the combination. | Changes; see studies | Small effect | 1 study | |||
Studies that measured skin pigmentation | ||||||
| Hair and Nail Health An animal study in lambs showed that methionine/cysteine infusion influenced follicle protein synthesis rates and mRNA expression in skin, consistent with L-cysteine's known role as a structural component of keratin in hair and nails. | Improves (the measure goes up) | Small effect | 1 study | |||
Studies that measured hair and nail health | ||||||
Key findings
- Antioxidant StatusImproves (the measure goes up)
- Erythrocyte Membrane IntegrityImproves (the measure goes up)
- Alcohol-Induced Oxidative DamageImproves (the measure goes down)
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- Grade C
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Studies cited
8 studies from PubMed
- Protective effects of cysteine, methionine and vitamin C on the stomach in chronically alcohol treated rats.
- L-cysteine supplementation prevents exercise-induced alterations in human erythrocyte membrane acetylcholinesterase and Na+,K+-ATPase activities.
- The beneficial effect of L-cysteine supplementation on DNA oxidation induced by forced training.
- L-cysteine supplementation protects the erythrocyte glucose-6-phosphate dehydrogenase activity from reduction induced by forced training.
- Does ascorbate/L-Cys/L-Met mixture protect different parts of the rat brain against chronic alcohol toxicity?
- Alcohol-induced oxidative stress and reduction in oxidation by ascorbate/L-cys/L-met in the testis, ovary, kidney, and lung of rat.
- Effect of simultaneous administration of vitamin C, L-cysteine and vitamin E on the melanogenesis.
- Transsulfuration, protein synthesis rate and follicle mRNA in the skin of young Merino lambs in response to infusions of methionine and serine.