Supplement analysis backed by scientific evidence · PT

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Limited evidenceJoints & skin

Keratin

Oral keratin (usually solubilized wool keratin, sold as Cynatine HNS) rests on a single small manufacturer-funded trial; the intuitive idea that eating hair protein makes hair is not how protein digestion works.

What the science says

  • Reduces hair loss and improves hair strength Limited evidence

    The one placebo-controlled trial commonly cited enrolled 50 women on 500 mg/day of solubilized keratin for 90 days and reported improvements in hair loss, hair strength, luster and nail appearance. It is small, short, industry-sponsored and has not been independently replicated — the definition of a limited evidence base.

  • Improves nail hardness and growth Limited evidence

    Nail outcomes in that same 50-person trial were secondary and largely subjective or investigator-rated. A 2023 systematic review of nutritional supplements for hair complaints found the field dominated by small, low-quality, sponsor-funded studies, and keratin was not among the ingredients with reproducible support.

  • Eating keratin delivers keratin to your hair Limited evidence

    Ingested keratin is digested to amino acids and small peptides like any other protein; it is not routed preferentially to follicles. Keratin is cysteine-rich, so a plausible framing is that it supplies sulfur amino acids — but adequate dietary protein already does this, and cysteine supplementation alone has not been shown to improve hair in well-nourished people.

Dosage & safety

Studied dose500 mg/day of solubilized keratin for 90 days is the dose used in the published trial. Products commonly supply 250-500 mg, usually bundled with biotin, zinc, copper and vitamin C, which makes attributing any effect to keratin itself impossible. Give any hair supplement at least 3-6 months before judging it — the hair cycle is that slow.
SafetyNo serious adverse effects reported at 500 mg/day; mild GI upset is the usual complaint. Sourced from sheep's wool, so it is not vegetarian and is a theoretical concern for wool/lanolin-sensitive individuals. The bigger practical risk is the high-dose biotin (often 5,000-10,000 mcg) packaged alongside it, which interferes with immunoassays and has caused falsely low troponin results and missed myocardial infarctions — stop biotin-containing products several days before blood testing. Sudden or patchy hair loss warrants a medical workup (iron deficiency, thyroid disease, androgenetic alopecia) rather than a supplement.

Scientific references

Where to buy

Double Wood Supplements, Keratin, 120 Capsules (250 mg per Capsule)

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