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Is Iodine Deficiency a Bigger Problem Than We Think?

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Iodine is important for thyroid health, fetal growth, mental health, and more. However, iodine intake is decreasing, especially in certain populations. Read on to learn the impacts of low iodine intake, who is at risk, and how to treat iodine deficiency.

Iodine is required to synthesize the thyroid hormones T3 and T4. Because of iodized salt programs, the United States has been considered iodine-replete since around the 1920s. However, iodine intake has been decreasing since 1971, when the National Health and Nutrition Examination Surveys (NHANES) began monitoring iodine status. In 1971, iodine levels determined from urine tests were 320 mcg/L (1). By 2010, average iodine concentration dropped to 144 mcg/L. Below 100 ug/L is considered deficient for an adult, while anything below 150 mcg/L is below optimal for pregnant women.

Iodine deficiency affects more than 2.2 billion people worldwide. In the Western world, iodine deficiency affects multiple demographics more than many practitioners realize (2):

  • In the NHANES studies, pregnant women and women of childbearing age had the lowest median iodine levels (3, 4, 5)
  • In a study of Boston mothers, 47 percent of breast milk iodine samples were insufficient (6)
  • In Europe, it’s estimated that up to 44 percent of the population may be iodine deficient (7)
  • In school-aged children in New Zealand, a whopping 83 percent were iodine deficient (8)

Patients Are Not Consuming Enough Iodine-Rich Foods

Table salt is fortified with iodine, but this method of mass supplementing may no longer be sufficient. First, although the consumption of salty, processed food has skyrocketed over the past several decades, these products are generally not made with iodized salt. Second, sea salt, which is becoming more popular, doesn’t contain iodine either. Furthermore, due to fear of hypertension, many patients are instructed to severely restrict salt intake (which is somewhat misguided, anyway).

Most of the world’s iodine is found in the oceans. Therefore, the richest dietary sources are from the sea: sea vegetables like kombu, nori, and kelp and saltwater fish and fish heads. Regular consumption of these sources is rare in the United States.

Dairy products contain a little iodine, but most of it comes from iodophor, a cleanser used to sterilize milk tanks, and from cow feed, which is supplemented with iodine in the United States.  Eggs are another minor source of iodine.

Are you getting enough iodine on your Paleo diet?

Who Is at Risk for Iodine Deficiency?

Considering the best dietary sources of iodine, specific demographics are susceptible to iodine deficiency.

Vegans and Vegetarians

Veganism is increasingly popular, comprising 0.5 to 6 percent of the U.S. population, according to various estimates. Estimates of vegetarians range from 2 to 10 percent of the population. Some of the most nutrient-dense foods are properly sourced animal products, and so it should come as no surprise that vegetarians and vegans are at risk for a number of nutrient deficiencies, including vitamin B12, calcium, zinc, vitamin A, vitamin D, and iodine.

Vegans are especially susceptible to iodine deficiency. In the literature, vegans repeatedly have low iodine intake and/or iodine deficiency (9, 10, 11, 12, 13). The only exceptions were vegans who consumed seaweed, a very rich source of iodine (12).

Vegans and vegetarians may also consume relatively high quantities of vegetables from the genus Brassica, including broccoli, kale, Swiss chard, and Brussels sprouts. These vegetables contain goitrogens, which in large doses inhibit iodine uptake by the thyroid. Therefore, even above-adequate iodine intake may not be enough to counter the goitrogen effects.

Paleo Dieters

The ideal Paleo diet should include saltwater fish and sea vegetables, but if these aren’t consumed on a regular basis, Paleo dieters may be susceptible to iodine deficiency, especially if they aren’t consuming any dairy products. In one study that compared a Paleolithic diet to the Nordic nutrition recommendations for two years, the Paleo dieters had significantly lower iodine status (14). Patients on a Paleo diet should be sure they are consuming adequate iodine-rich foods.

Pregnant Women

During pregnancy, iodine requirements increase by 50 percent, due to an increased glomerular filtration rate and the needs of the fetus. If women aren’t consciously making an effort to consume iodine-rich foods, their diets may fall short. Between 1971 and 2008, the percentage of pregnant women with severely deficient urinary iodine levels (<50 mcg/L) increased from 4 to 15 percent (15).

A fetus’s thyroid isn’t developed until after the first trimester, and so he is completely dependent upon the mother’s properly working thyroid, including replete iodine. Iodine is especially important for fetal brain development and proper myelination of the central nervous system.

Those with High Exposure to and/or Suboptimal Detoxification of Environmental Toxins

Environmental toxins may contribute to iodine deficiency in Western populations. Perchlorates, thiocyanates, and nitrates all compete with iodine in the sodium-iodine symporter present in thyroid and lactating breast tissue (16). Therefore, people with high exposure to these toxins or people who have trouble properly detoxing these substances may have trouble incorporating iodine into the thyroid.

Perchlorate is used as an oxidizer for rocket fuels and a propellant in explosives. In the NHANES 2001–2002 study, perchlorates were present in all 2,820 urine samples (17). Several studies have found no association with perchlorate levels and thyroid function (18, 19), except when also in the context of iodine deficiency (20).

Thiocyanates are found in vegetables in the genus Brassica, as discussed above, but they are also present in cigarette smoke. Nitrates are found in drinking water, processed meats, and some leafy and root vegetables.

Risks of Iodine Deficiency

Iodine deficiency disrupts thyroid function and inhibits proper production of T3 and T4, which can lead to a variety of health problems.

Subclinical Hypothyroidism

Subclinical hypothyroidism (SCH) is generally diagnosed from high levels of thyroid-stimulating hormone (TSH) but normal T3 and T4 levels. Symptoms of this condition are varied and can include mental slowing, depression, dementia, weight gain, dry skin, hair loss, cold intolerance, hoarse voice, irregular menstruation, infertility, muscle stiffness, and pain. Untreated SCH can lead to clinical hypothyroidism and swelling of the thyroid (goiter).

SCH during pregnancy increases the risk of miscarriage, gestational diabetes, and preterm delivery (21, 22, 23). The prevalence of SCH during pregnancy may be as high as 15 percent (24), but proper diagnosis is challenging. Appropriate levels of TSH during different trimesters are not well established. Due to the suppressed immune system that accompanies pregnancy, thyroid antibodies, which may actually indicate an autoimmune thyroid disease versus iodine deficiency, may not be detectable.

Brain/Cognitive Problems

Especially important for developing brains, iodine is critical for babies in utero and young children. Mild iodine deficiency during pregnancy is associated with decreased IQ and increased risk of attention deficit disorder in the children (25, 26). Severe iodine deficiency can result in cretinism, which is characterized by mental retardation, dwarfed state, bone dystrophy, and low basal metabolism. Iodine supplementation during pregnancy has been shown to reduce neonatal mortality and improve IQ scores (27, 28).

Breast Cancer

Iodine concentrations are higher in breast tissue even than in the thyroid, to provide plenty of iodine for the breastfeeding infant (29). There is some evidence in animals that iodine-deficient breast tissue is more susceptible to the effect of carcinogens and therefore increased risk of cancer (30). The Japanese, who probably have the highest consumption of iodine in the world, have less than one-third the incidence of breast cancer than do Americans (31). When these women emigrate to the United States and adopt the Standard American Diet, their breast cancer risk rises to that of other American women.

Testing for Low Iodine

Many conventional doctors measure iodine using a spot urine check. However, this won’t give an accurate picture of iodine levels. One study reported that 12 or more spot urine checks are needed to achieve precision within 20 percent (32).

I prefer to test for iodine levels using a combination of three tests:

  • First, a 24-hour urine iodine test involves collecting and then testing entire urine output for 24 hours.
  • Second, a hair iodine test is a good marker for long-term iodine status (33).
  • Last, serum thyroglobulin (not the antibody), reversely correlates well with iodine levels.

Treatment for Low Iodine

Patients who are iodine-deficient need to increase both iodine and selenium intake, preferably from foods.

Selenium helps protect against iodine toxicity by ensuring that glutathione peroxidase activity in the thyroid is adequate to avoid cytotoxicity of hydrogen peroxide (34). Selenium is also required for the deiodinase enzymes that convert T4 to T3. Good dietary sources of selenium include Brazil nuts, crimini mushrooms, cod, shrimp, tuna, halibut, salmon, scallops, chicken, eggs, shiitake mushrooms, lamb, and turkey.

To increase iodine intake, kelp flakes can be used in place of salt, while other forms of seaweed can be used for flavoring foods.

Over-supplementing with iodine can contribute to Hashimoto’s disease or hyperthyroidism, especially when accompanied by selenium deficiency. Long-term supplementation with selenium is also not advisable, since it leads to fatigue, GI upsets, mild nerve damage, and more (35).

If supplementation is necessary, start with a small dose of iodine, one 325 mcg kelp tablet per day. Increase the dose by one tablet every three weeks up to 3 tablets a day, unless hyperthyroid-like or detox symptoms occur. Once the patient improves, the dose can slowly be scaled down again. Very short-term supplementation of selenium, 200 mcg per day for a couple months, can be safe but requires extra precaution.

Frequently Asked Questions:

How common is iodine deficiency?

Iodine deficiency affects more than 2.2 billion people worldwide. In the Western world, iodine deficiency affects multiple demographics more than many practitioners realize


  1. Hi Chris:
    Do you run the 24 hr urine through a specialty lab or standard lab (?Labcorp, etc) would suffice?
    And please clarify trusted sources of Kelp (brands?)

    Many thanks

  2. Low nocturnal basal temperatures is a good way to measure sub clinical hyopothyroid. Also fibercystic beast diseases and loss of outer third of eyebrow. I think most all aging adults suffer with lowbasal temperatures so you find room thermostat set at 79 while they wear sweaters year round. I now take 2 mg daily with selenium.

  3. I wonder about supplementation for someone with Hashimoto’s for 45 years. It seems like this is more complicated than a simple deficiency?

  4. Dr Sherri Tenpenny, DO, says in her Youtube video that thyroid normalizes after about 48 hours of upping iodine. Check it out.
    I know of at least one woman who had a miscarriage BECAUSE of low thyroid levels that made it impossible for her to carry. Low thyroid and low iodine are frequent partners.

    There is NO wolff-chaikoff (sp?) effect.

  5. Thanks for bringing this up.
    Would be nice to have some good seaweed recipes to go along with this article. This is something really lacking from my diet.

  6. After a couple of years of doing a paleoish diet I realized I probably wasn’t getting any iodine. So now my salt contains 25% iodized salt and 75% Himalayan and I take 1 capsule of Now full spectrum minerals every night. I didn’t want to over do it, but I didn’t want to worry that I was getting close to nothing as well so this seemed like a pretty good balance.

  7. Good article! I see Functional Medicine as the medicine of the future. I have had a fellowship in biochemistry and nutrition is really applied biochemistry. The only thing you omited was to mention that selenium is necessary for activity of the glutathione enzymes.

  8. i have an Rx for LDN, but i don’t seem to be doing much better. Losing weight. MD hasn’t bothered to look at my diet or supplements – after 6 months still not up to normal 4.5 mg dose… worried & can’t afford to keep experimenting with medical professionals. Sad this one hasn’t bothered to explain what or why he’s doing &/or not doing & of course my medical insurance is a waste of time as the protocol only test TSH – totally inadequate. i guess i’m not important enough or rich enough to get help. very frustrated. As your article points out the info is contradictory.

  9. Great article, Chris!

    Pretty sure I’m lower in iodine, as I don’t consume dairy & am spotty in my seaweed consumption. Will get on the kelp flakes train! QUESTION: you say supplementing selenium long-term can be a problem…. but what about long-term consumption of selenium-rich foods like Brazil nuts? Curious if you’re just referring to actual supplemental forms of these nutrients with that caution …