Evidence supporting the use of: Cysteine
For the body system: Nails

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Table of Contents

Synopsis

Source of validity: Scientific
Rating (out of 5): 3

Cysteine is an amino acid that serves as a building block for the synthesis of keratin, the primary structural protein in nails. Its role in supporting nail health is supported by basic biochemical and physiological research: keratin contains a high proportion of cysteine residues, which form disulfide bonds that provide strength and rigidity to the nail plate. Deficiency in cysteine or its precursor, methionine, has been associated with brittle nails in some observational studies and animal models. Oral cysteine supplementation (often as N-acetylcysteine or L-cysteine) is commonly included in dietary supplements marketed for nail health, and some small studies and clinical reports suggest that supplementation may improve nail strength and reduce brittleness, particularly in individuals with poor dietary intake.

However, robust clinical trials in healthy populations are limited, and the overall quality of evidence is moderate. The biological rationale is strong given cysteine’s structural role in keratin, but direct evidence for substantial benefit from supplementation in individuals with otherwise adequate protein intake is not conclusive. In summary, the use of cysteine to support the nail body system is justified by scientific understanding of nail biology and some supportive, though not definitive, human data.

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