Iodine — An Essential Mineral, But How Much Do We Need?
Iodine doesn't get nearly as much attention as vitamin D, magnesium or omega-3s. Yet it is essential for one of the body's most important systems: the thyroid gland needs iodine to make thyroid hormones.
Too little iodine can cause hypothyroidism and enlargement of the thyroid, or goiter. But iodine is unusual among nutrients because too much can also interfere with thyroid function.
That makes the question more complicated than simply asking whether iodine is good for us.
Where Do We Get Iodine?
Major sources include iodized salt, seafood, dairy products and some breads.
One reason some functional-medicine doctors have become concerned about iodine is that many health-conscious people have reduced their use of salt—and specialty salts such as sea salt and Himalayan salt may not be iodized.
The recommended dietary allowance for most adults is 150 micrograms (mcg) a day.
William Davis — Are We Getting Enough?
Dr. William Davis, author of Wheat Belly, has argued for years that iodine deficiency is more common than generally recognized.
His reasoning is straightforward. Iodized salt dramatically reduced iodine deficiency in the United States, but many people subsequently reduced their salt intake or switched to non-iodized specialty salts.
Davis recommends iodine intakes above the standard 150 mcg RDA. His program describes 400–500 mcg daily as a typical target and cautions against exceeding 1,000 mcg.
Davis also cautions that people with Hashimoto's disease or certain thyroid nodules require special care with iodine.
I find his argument worth considering, particularly for people who eat little seafood or dairy and don't use iodized salt.
Functional Medicine Doesn't Have One View
Other functional and integrative practitioners also pay considerable attention to iodine, but they don't necessarily agree about supplementation.
Izabella Wentz, PharmD, who specializes in Hashimoto's disease, calls iodine something of a “Goldilocks” nutrient: too little can impair thyroid function, while too much can be harmful, particularly for susceptible people with autoimmune thyroid disease. She is considerably more cautious about higher-dose iodine supplementation than Davis.
This disagreement is important. It reminds us that recognizing iodine as essential doesn't automatically tell us how much is optimal for a particular person.
What Do Mainstream Thyroid Experts Recommend?
The American Thyroid Association recommends 150 mcg a day for most adults and says that the typical U.S. diet generally provides enough iodine.
It advises against routine iodine or kelp supplements containing more than 500 mcg per day, while the established tolerable upper intake level for adults is 1,100 mcg per day.
This doesn't mean that 501 mcg suddenly becomes toxic. Rather, it reflects concern that higher supplemental doses have not demonstrated routine thyroid benefits and may cause problems in susceptible people.
Who Should Be Particularly Careful?
Extra iodine deserves particular caution in people with Hashimoto's thyroiditis, Graves' disease, thyroid nodules or other existing thyroid disorders.
Age also matters. The American Thyroid Association identifies older adults as one of the groups that can be more susceptible to adverse effects from excess iodine.
Kelp supplements deserve special attention because the amount of iodine they contain can be high.
The Takeaways
Iodine is essential, and avoiding deficiency clearly matters.
I also think William Davis raises an interesting question: as people reduce iodized salt and change their diets, are some of us getting less iodine than we realize?
But like many supplements, more is not necessarily better. The difference between the standard recommendation of 150 mcg and the higher amounts advocated by Dr. Davis illustrates how much disagreement remains about optimal intake.
For someone considering an iodine supplement—particularly someone with a thyroid condition—it makes sense to look first at dietary iodine intake and thyroid health rather than simply starting a high-dose supplement.
Learn More
Dr. Davis discusses iodine's role in producing thyroid hormones and other factors that can affect thyroid function.
Izabella Wentz explains why both too little and too much iodine can be problematic, particularly for people with Hashimoto's disease.
A detailed evidence-based review of iodine requirements, food sources, deficiency, supplements and the risks of excessive intake.
Explains recommended iodine intake and why excessive supplementation can cause thyroid problems.
Videos
Dr. William Davis explains why he believes iodine deficiency may be more common than generally recognized and why he pays particular attention to iodine intake.
Dr. Angella Mazza discusses iodine supplementation and explains why both too little and too much iodine can affect thyroid health, particularly in people with Hashimoto's disease, thyroid nodules, or goiters.