Iodine and Hair: The Thyroid Link, How Much You Need & Safety

Iodine isn't a hair nutrient on its own. It's an ingredient your body needs to make thyroid hormones, and thyroid hormones do act directly on hair follicles. Both too little and too much thyroid activity can show up as hair shedding.

Here's how iodine, thyroid hormones and hair connect, how much you need, and why taking extra isn't a hair strategy.

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Key Takeaways

• Iodine is essential for making thyroid hormones.
• In lab studies on human hair follicles, thyroid hormones prolonged the growth phase and boosted hair-cell proliferation and pigment production.
• Thyroid dysfunction, underactive or overactive, can cause widespread hair shedding.
• Recommended intake is 150 μg a day for adults. Above that is generally well tolerated, but some people can develop thyroid problems from excess iodine.

What Is Iodine?

Iodine is a micronutrient that the thyroid uses to make hormones. It comes mainly from the diet, through fortified foods and from foods that naturally contain it.

Iodine, Thyroid And Hair

Thyroid hormones act on the hair follicle directly. That's the real link between iodine and hair: iodine supports the hormones, and the hormones influence the follicle. It does not mean that more iodine means more hair.

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How To Get Enough

• From food. Seafood, and foods fortified with iodine such as salt, dairy products and bread.
• Don't megadose. Talk to your doctor before taking iodine supplements.
• See a doctor if you're losing hair. Thyroid problems are one of the causes a doctor can check with a blood test.

What The Research Shows

Thyroid Hormones Act On Hair Follicles

Researchers cultured human scalp hair follicles and treated them with thyroid hormones. T4 increased the proliferation of hair matrix cells, both T3 and T4 reduced cell death, and T4 prolonged the anagen (growth) phase in vitro. T3 and T4 also stimulated melanin synthesis in the follicle (van Beek et al., 2008). This is lab work on follicles from women undergoing facelifts, not a trial of iodine.

Thyroid Problems And Hair Shedding

A review reports that hyperthyroidism, hypothyroidism and drug-induced hypothyroidism can all cause widespread hair shedding, and that thyroid disorders' impact on hair is probably underestimated (Hussein et al., 2023).

Iodine Intake: Enough And Too Much

The recommended daily iodine intake is 150 μg for adults who are not pregnant or lactating. The main sources are iodine-fortified foods such as salt, dairy products and bread, and naturally rich foods such as seafood. Intakes above the threshold are generally well tolerated, but in susceptible people, including those with existing thyroid disease, older adults and neonates, excess iodine can cause hypothyroidism or hyperthyroidism (Leung & Braverman, 2014).

Kelp is often marketed as an iodine source; see our article on kelp and hair for what the research says about it.

See also: Boron for Hair: What the Research Actually Shows · Manganese for Hair: Benefits, Food Sources & How Much You Need

Frequently Asked Questions

Does iodine help hair growth?

Iodine supports thyroid hormone production, and thyroid hormones act on hair follicles in the lab. We found no trial showing that iodine supplements grow hair.

Can iodine deficiency cause hair loss?

Thyroid dysfunction can cause hair shedding. If you're losing hair, a doctor can check your thyroid.

Can you take too much iodine?

Yes, particularly if you have thyroid disease. Talk to your doctor before taking iodine supplements.

References

1. van Beek N, Bodó E, Kromminga A, et al. Thyroid hormones directly alter human hair follicle functions: anagen prolongation and stimulation of both hair matrix keratinocyte proliferation and hair pigmentation. J Clin Endocrinol Metab. 2008. PubMed
2. Hussein RS, Atia T, Bin Dayel S. Impact of Thyroid Dysfunction on Hair Disorders. Cureus. 2023. PubMed
3. Leung AM, Braverman LE. Consequences of excess iodine. Nat Rev Endocrinol. 2014. PubMed