Iodine
Real iodine deficiency does affect hair via thyroid — but in iodized-salt populations, supplementing extra iodine is unnecessary and can harm.
How Iodine works — and how well we know it
Iodine is required for thyroid hormone synthesis. Thyroid dysfunction (both hyper- and hypothyroidism) causes hair loss — but supplementing iodine in iodine-replete adults will not improve thyroid hormone production and can trigger thyroid dysfunction.
oral
150 mcg/day (RDA). Iodized salt provides adequate intake in most developed countries.
Trace mineral; RDA 150 mcg/day. Critical for thyroid hormone synthesis.
Patients in genuinely iodine-deficient regions.
Evidence distribution across 1 claims
Why the grade is F. Iodine deficiency is rare in iodized-salt populations. Supplementation in iodine-replete adults can paradoxically cause thyroid dysfunction.
Every claim, traced back to its source
We took every major claim made about Iodine and matched it to the specific experimental model behind it. Click a claim to see the model, the finding, and our assessment of how much weight it deserves.
1 claims · evidence-by-evidence breakdown
1Open-LabelWeight: HighIodine excess can trigger thyroid dysfunctionIodine has a narrow therapeutic window. Bundling it in hair supplements without measurement is risky.
Established endocrinology — Wolff-Chaikoff effect and iodine-induced hyperthyroidism.
Chronic supplementation in iodine-replete adults can trigger autoimmune thyroiditis and hyperthyroidism in susceptible individuals.
Hair-supplement bundling of iodine without regard to dietary intake is the same overzealous logic as the iron and selenium examples. There's a sweet spot, not a 'more is better' relationship.
- Leung AM, Braverman LE (2014). Nat Rev Endocrinol PMID 24342882
What's still missing from the science
- RCT of iodine supplementation for AGA in non-deficient adults.
Our verdict on Iodine
Not in our formulary yet
We don't carry this ingredient. We only formulate around actives where the evidence — and the safety profile — is strong enough to recommend with confidence. As the data matures, we may revisit.
Related treatments
How does Iodine stack up against its closest peers?
A genuine cause of reversible hair shedding in iron-deficient patients — but useless and potentially harmful if your iron stores are normal.
Read the breakdown →A botanical 5-alpha reductase inhibitor whose only high-quality trials (in BPH) showed no benefit over placebo; the positive AGA data are small and low-quality.
Read the breakdown →One small Malaysian RCT showed a hair-count increase. Never replicated. Used by Nutrafol to justify its tocotrienol content.
Read the breakdown →