mineral · for brittle nails
Iron
Nail cells need oxygen to grow, and low iron starves them of it.
Say that in clinical terms
Iron is essential for hemoglobin production and oxygen delivery to nail matrix cells. Iron deficiency causes nail bed hypoxia, resulting in thin, concave (koilonychia), and brittle nails due to impaired keratin synthesis.
How strong is the research?
3 papers read.
Who was studied: People turning up at a clinic with visible nail abnormalities, mostly iron-deficient.
PubMed returns zero results for iron bisglycinate combined with nails. The 74-paper iron bisglycinate literature in humans covers exclusively anemia, iron status in pregnancy, and gastrointestinal tolerability. The 2024 Karger nail supplements review (already in the known papers) explicitly enumerates the four compounds with nail-specific evidence and does not include iron. No RCT of any iron form — including ferrous sulfate — was found that used brittle nails or nail quality as a primary outcome. Iron deficiency is associated with nail changes (koilonychia) in case literature, but that association has not been tested in an interventional trial.
How much to take
daily on empty stomach
18–36 mg
Iron deficiency is a common cause of koilonychia (spoon nails) and nail brittleness. Test ferritin levels.
Before you take it
- NIH ODS Tolerable Upper Intake Level (UL) for iron is 45 mg/day for adults (all sources combined: food and supplements).
- Levothyroxine interaction: concurrent ingestion significantly reduces levothyroxine efficacy; separate iron and levothyroxine by at least 4 hours.
- Tetracycline and fluoroquinolone antibiotic interaction is asymmetric: take the antibiotic at least 2 hours BEFORE iron, or at least 4–6 hours AFTER iron — not a simple equal-interval separation.
- Levodopa interaction: iron may reduce levodopa absorption via chelation; separate administration times (specific interval not fixed in NIH ODS guidance).
- Proton pump inhibitors (e.g., omeprazole, lansoprazole) reduce gastric acid and may impair non-heme iron absorption, potentially reducing efficacy of oral iron supplementation.
- Hereditary hemochromatosis (HFE gene mutation): iron supplementation is contraindicated; risk of iron overload, organ damage.
- GI side effects (constipation, nausea, abdominal discomfort) are common with oral iron; iron bisglycinate is better tolerated than ferrous sulfate in comparative trials but is not side-effect-free.
- Accidental ingestion by children can be fatal; child-resistant storage is essential.
- Iron supplementation without confirmed deficiency (serum ferritin or CBC) has no established benefit for symptom relief and risks cumulative toxicity approaching or exceeding the 45 mg/day UL when combined with dietary iron.
When to take it
Best taken: empty stomach
What we make of it
The strong evidence is for spoon-shaped nails in outright anaemia, which is a different problem.
The detail
The iron and nail link is well established for koilonychia — spoon-shaped nails in iron-deficiency anaemia. That is a specific structural change, not the splitting and peeling most people mean by brittle nails.