Solubilized keratin is the protein of hair, nail and skin, taken apart so the gut can absorb it. Three months brings fewer hairs shed, harder nails, better-hydrated and smoother skin — cosmetic, not life-extending. Almost all trials were funded by the sellers and none reproduced independently. Harms recorded so far are minor; the biotin packaged with it distorts common blood tests. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Ferritin | 70–100 ng/mL | Low iron stores independently cause shedding |
| Thyroid-stimulating hormone (TSH) | 0.5–2.0 mIU/L | Both under- and overactive thyroid cause hair and nail change |
| Free T4 | 1.0–1.5 ng/dL | Confirms thyroid status when TSH is borderline |
| Serum zinc | 90–120 µg/dL | Deficiency causes shedding; excess from stacking depletes copper |
| Serum copper | 80–100 µg/dL | Detects copper depletion caused by stacked zinc |
| Serum selenium | 100–140 µg/L | Both deficiency and excess cause hair and nail loss |
| 25-hydroxyvitamin D | 40–60 ng/mL | Low status is associated with several hair loss patterns |
| Complete blood count | Haemoglobin 13.5–15.0 g/dL (women), 14.5–16.0 g/dL (men) | Detects anaemia driving diffuse shedding |
| Plasma homocysteine | 6–8 µmol/L | Reflects sulfur amino acid handling at protein-supplement doses |
| Estimated glomerular filtration rate (eGFR) | Above 90 mL/min/1.73m² | Sets whether a protein-level dose is appropriate |
| Hair pull test | No established target; track change from own baseline count | The endpoint that trials actually moved |
Cadence: Baseline before starting; photographs and nail count repeated at 45 and 90 days; thyroid function and ferritin rechecked at three months if either was borderline; six to twelve months thereafter for anyone continuing long term.