Evidence supporting the use of: L-cysteine
For the health condition: Convalescence

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Synopsis

Source of validity: Scientific
Rating (out of 5): 2

L-cysteine is an amino acid that plays a vital role in protein synthesis and the production of the antioxidant glutathione. Its use in convalescence—recovery after illness or surgery—is primarily based on its biochemical functions. During periods of recovery, the body's demand for amino acids increases to repair tissues, support immune function, and manage oxidative stress. L-cysteine, as a precursor to glutathione, helps replenish antioxidant defenses that may be depleted during illness.

Several studies have shown that glutathione levels can drop during severe illness or stress, leading to increased oxidative damage and delayed recovery. Supplementation with L-cysteine (or its more stable form, N-acetylcysteine, NAC) has been investigated in clinical settings, particularly for patients with chronic respiratory diseases, critical illness, or after surgery. Some randomized controlled trials suggest that NAC supplementation can reduce hospital stays, improve immune function, and support recovery, though the evidence is stronger for NAC than plain L-cysteine.

However, while there is a plausible scientific rationale and some supporting data, the evidence base for routine L-cysteine supplementation specifically for general convalescence is modest and not universally endorsed by guidelines. More robust clinical trials are needed to define optimal dosing, patient selection, and outcomes. Thus, the evidence rating is moderate (2/5): there is scientific basis and limited clinical evidence, but not strong or conclusive support.

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