Synopsis

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

L-cysteine is an amino acid involved in various metabolic pathways, notably as a precursor to glutathione, a critical intracellular antioxidant. Its use for fatigue is primarily based on its role in supporting glutathione synthesis, which is essential for combating oxidative stress and maintaining mitochondrial function. Some scientific studies suggest that oxidative stress and mitochondrial dysfunction can contribute to fatigue, particularly in chronic fatigue syndrome (CFS) and related conditions.

Supplementation with N-acetylcysteine (NAC), a derivative of L-cysteine, has been more widely studied than L-cysteine itself. NAC has demonstrated some promise in reducing fatigue in certain populations, such as individuals with multiple sclerosis or CFS, due to its ability to boost glutathione levels. However, direct evidence supporting the use of plain L-cysteine for fatigue is limited, and most clinical data is extrapolated from studies with NAC.

Overall, while there is a plausible biochemical rationale and some preliminary clinical evidence (mainly using NAC), robust clinical trials specifically evaluating L-cysteine for fatigue are lacking. Therefore, the scientific evidence is modest (rated 2/5), and more research is needed to confirm its efficacy for this purpose.

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