6 min read
A lot of kitchens made the same quiet swap over the last decade: the old cylinder of iodized table salt went out, and a grinder of pink Himalayan or flaky sea salt came in. It looks nicer and tastes great. What most people do not realize is that the switch may have removed one of the main sources of iodine in their diet.
That small change is a good way into a bigger topic: iodine and selenium for thyroid health. These two minerals do much of the behind-the-scenes work that lets your thyroid make and manage its hormones. Both are easy to get too little of, and just as easy to overdo.
Quick answer: Your thyroid needs iodine to make thyroid hormones, and selenium is concentrated in the thyroid, where it supports the enzymes that handle those hormones. Most adults can meet their needs with iodized salt, dairy, seafood, eggs, and a varied diet. Both minerals have upper limits, and too much of either can cause problems, so more is not better, and anyone with a thyroid condition should talk with their clinician before supplementing.
[IMAGE: Iodized salt, a small bowl of Brazil nuts, eggs, and a piece of cod arranged on a kitchen counter | alt: food sources of iodine and selenium for thyroid health]
Iodine and Selenium for Thyroid Health: How They Work Together
Think of iodine as the raw material. Your thyroid uses it to build its hormones, which help regulate metabolism throughout your body. Without enough iodine, the thyroid cannot make enough hormone, and over time it may enlarge (a goiter) as it tries to keep up.
Selenium is more like the maintenance crew. According to the NIH Office of Dietary Supplements, the thyroid holds more selenium than any other organ in the body. It is part of enzymes that help activate thyroid hormones and protect the gland from damage during hormone production. The two minerals are linked, which is why it makes sense to think about them together.
Iodine: Where Americans Actually Get It
Adults need 150 mcg of iodine a day, according to the NIH iodine fact sheet. In the U.S., iodized salt contains 45 mcg of iodine per gram, and a quarter teaspoon provides roughly 78 mcg. Seaweed, cod, dairy, and eggs are other good sources.
Here is the catch. The NIH notes that specialty salts, such as sea salt, kosher salt, Himalayan salt, and fleur de sel, are not usually iodized. And a 2017 review in the Cleveland Clinic Journal of Medicine points out that nearly 70% of the salt we eat comes from processed food, which is typically made with non-iodized salt. So you can eat plenty of salt and still get very little iodine from it.
The same review notes that the share of women of childbearing age with moderate iodine deficiency rose from 4% to 15% between the 1970s and the 1990s. Groups more likely to fall short include:
- People who skip dairy, seafood, and eggs, including many vegans. Our guide to nutrients worth watching on a plant-based diet covers practical fixes.
- People who use only specialty salts at home and rarely eat seafood or dairy.
- Pregnant and breastfeeding women, whose needs rise sharply.
Pregnancy and Breastfeeding: The Time Iodine Matters Most
Iodine needs climb to 220 mcg a day during pregnancy and 290 mcg while breastfeeding. Yet in a 2018 analysis in Nutrients, only 17.8% of pregnant women in the U.S. used a dietary supplement containing iodine. Many prenatal vitamins do not help, either: the NIH reports that only 34 of 59 top-selling prenatal supplements contained iodine.
If you are pregnant, planning to be, or breastfeeding, check your prenatal label and ask your provider about iodine. We cover more on this stage of life in Postpartum Nutrition: What New Moms Need While Breastfeeding.
Selenium: A Little Goes a Long Way
Adults need 55 mcg of selenium a day. The NIH lists tuna at 92 mcg per 3-ounce serving, sardines at 45 mcg, ham at 24 mcg, and a large egg at 15 mcg, so a typical mixed diet often covers it without much effort.
Then there are Brazil nuts. The NIH reports an average of 544 mcg of selenium per ounce, which is about 6 to 8 nuts, although actual amounts vary widely from nut to nut. That single ounce is well above the adult upper limit of 400 mcg a day. A Brazil nut here and there is a fine way to get selenium, but eating a handful every day is not a good habit.
Why More Is Not Better for Your Thyroid
This is the part supplement marketing rarely mentions. With both minerals, the safe range is narrower than people assume.
Too much iodine
The adult upper limit for iodine is 1,100 mcg a day. The NIH explains that high intakes can cause some of the same problems as low intakes, including goiter, elevated TSH, and hypothyroidism. Kelp and seaweed supplements deserve extra caution, since it is easy to take far more iodine than you intended.
Too much selenium
Selenium toxicity, called selenosis, can cause hair loss, brittle nails, garlic-smelling breath, a metallic taste, skin rash, nausea, and fatigue. It is not just theoretical. In 2008, according to the NIH, 201 people had severe reactions after taking a liquid supplement that contained 200 times the amount of selenium listed on the label.
That is a big reason to be wary of stacking products. A multivitamin, a “thyroid support” blend, and daily Brazil nuts can add up quickly. We explain the broader problem in why most multivitamins have too much.
What If You Already Have a Thyroid Condition?
If you have hypothyroidism, Hashimoto’s, Graves’ disease, or another thyroid condition, talk with your clinician or endocrinologist before adding iodine or selenium. Research on selenium for autoimmune thyroid disease is mixed. The NIH notes that selenium lowered thyroid antibody levels in some trials, but the American Thyroid Association recommends against selenium supplements for pregnant women with thyroid autoimmunity.
Some medications also interact with these minerals. Our post on medications that can lower vitamin levels explains why it pays to review your full list with your pharmacist.
For healthy adults who want a steady baseline, a multivitamin near the Daily Value is usually enough. Vitamin100, for example, provides 150 mcg of iodine and 55 mcg of selenium, both at 100% of the Daily Value, with no extra thyroid “support” blends. If you already eat Brazil nuts daily or take kelp, count those too.
Frequently Asked Questions
Does sea salt or Himalayan salt have iodine?
Usually not in meaningful amounts. The NIH notes that specialty salts such as sea salt, kosher salt, and Himalayan salt are not usually iodized. If you love them for flavor, consider keeping iodized salt for everyday cooking or make sure you get iodine from dairy, eggs, or seafood.
How many Brazil nuts a day is safe?
Because one ounce (about 6 to 8 nuts) averages 544 mcg of selenium, well above the 400 mcg upper limit, most people are better off with just one or two nuts, and not necessarily every day. Selenium content varies a lot from nut to nut, so moderation is the safest approach.
Should I take iodine for my thyroid?
Not without a reason. Most adults get enough iodine from food and iodized salt, and too much can harm the thyroid. If you have a thyroid condition, or are pregnant or breastfeeding, ask your clinician what makes sense for you.
Can I get too much iodine from a multivitamin and food?
For most people, no. A multivitamin with 150 mcg plus a normal diet stays well under the 1,100 mcg upper limit. The risk comes from adding kelp or high-dose iodine supplements on top.
The Bottom Line
Iodine and selenium are small nutrients with a big job, and your thyroid depends on both. For most people, the fix is simple: keep some iodized salt in the kitchen, eat dairy, eggs, and seafood if you can, enjoy the occasional Brazil nut, and skip mega-dose “thyroid support” products. If you have a thyroid condition or are pregnant, your clinician should be part of the plan.
Sources
- Iodine Fact Sheet for Health Professionals, NIH Office of Dietary Supplements, 2024
- Selenium Fact Sheet for Health Professionals, NIH Office of Dietary Supplements, 2025
- Iodine deficiency: Clinical implications, Cleveland Clinic Journal of Medicine, 2017
- Use of Iodine-Containing Dietary Supplements Remains Low among Women of Reproductive Age in the United States: NHANES 2011 to 2014, Nutrients, 2018
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This article is for general education and is not a substitute for advice from your healthcare provider.