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The Question of Iodine

Updated: Nov 9, 2022

By Dr. Timothy Trader, ND, PhD

Your thyroid gland needs iodine to produce thyroid hormones, which regulates your metabolic rate, which affects your heart, muscles, digestive function, brain maturation, and bone maintenance. In developing countries around the world, the number-one thyroid condition is hypothyroidism (1), caused by consuming foods grown in soils that are deficient in iodine (2). Because of the low iodine in their diets, the thyroid glands of people in developing countries tend to function below full capacity.

In western industrial countries, the problem of iodine deficiency was presumably solved by fortifying salt with iodine, beginning in the early 1920s. (3). Though, a new problem came about soon after the introduction of iodized salt, autoimmune thyroiditis, otherwise known as Hashimoto’s disease, which is the most common thyroid issue in industrial nations. Because of the ever-increasing use of iodized salt, there was also an increase of iodine in the diet. This overconsumption of iodine causes autoimmune thyroiditis (4, 5), at least in part. Ingesting gluten may also play a partial role in Hashimoto’s disease (6) as well as other issues, but the main problem is the excessive iodine consumption. Unlike the iodine deficiency causing hypothyroidism in the developing countries, the industrial nations most common thyroid issue is Hashimoto’s autoimmune thyroiditis due to excessive iodine intake (7).

What to do about iodized salt

Today, an ever-increasing part of the population is interested in being healthier. Many have decided to stop or at least decrease their salt intake. The reasons are numerous, as salt has been implicated in high blood pressure (8), edema (9), stroke (10), heart disease (11), osteoporosis (12, 13), stomach cancer (14), kidney disease (15), and renal stones (16, 17), to name a few. While this reduction in salt intake seems to be a good idea, it also reduces the iodine in the diet, and we see some of the problems with an insufficient iodine nutrient level creeping up on us. As in the developing countries, most fruits and vegetables are grown in iodine-deficient soils worldwide (2, 18).

In response, those who are choosing to do without salt are looking into ways to ensure they are getting enough of this vital nutrient. In the United States, the recommended daily allowance (RDA) for an adult is 150 micrograms of iodine a day. I know of no nutritional organization that recommends more than 600 micrograms a day of iodine, and the Food and Nutrition Board of the Institute of Medicine put an upper intake level at 1,100 micrograms for adults. In other words, they regard anything more than a milligram of iodine to be hazardous to your health (19). The bottom line to all of this is we don’t need much, and even without consuming iodized salt, it can be fairly easy to get too little or too much.

A new theory

A new trend has emerged, theorizing that we need more iodine than what is recommended, and it has caught the eye of many health seekers. The theory promises better health, more energy, better detoxification from modern-day toxins, prevention of breast cancer, and enhanced recovery from fibrocystic breast disease, Graves’ disease, Hashimoto’s disease, and other ailments.

What has been deemed “The Iodine Project” asserts that we need 12 to 50 milligrams of iodine a day. Note the unit: This is not micrograms; this is milligrams (some 10 to 45+ times more than the IOM’s upper recommended limit). As far as the basis behind this high iodine theory, we find it published only in non-peer-reviewed magazines. Nothing has been reported in mainstream medical journals, and yet this theory purports to be scientifically backed. Let’s see what the science really says about all of this …

Is more iodine an answer?

Too much iodine can be toxic (20). Excess iodine is classified as being anything above 1.1 milligrams a day (21). Again, this can be as little as just over two percent of what is suggested by The Iodine Project. Can you imagine what taking 45 times the toxic threshold can mean to your health? Some signs that you have taken too much iodine can be a brassy taste in the mouth, increased salivation, and gastrointestinal irritation, including diarrhea. Long-term iodine toxicity can lead to acneiform skin lesions, goiter, hair loss, thyroid diseases and cancer.

As stated earlier, too much iodine can cause thyroid problems (22). Excess iodine can do one of two things. The first is to ramp up your thyroid production, like in Graves’ disease (23). This is hyperthyroidism, which is also called thyrotoxicosis (24), where the thyroid keeps accepting the iodine and puts out more thyroid hormone than is needed. This can show up as anxiety, hand tremor, heat sensitivity, weight loss, puffy eyes, enlarged thyroid (known as a goiter) and cognitive impairment. This is not a healthy reaction; this is a serious problem.

The second possibility is that high iodine can actually slow down the thyroid. High iodine is significantly responsible for the high rates of Hashimoto’s autoimmune thyroiditis (25). One study puts it rather bluntly, “More than adequate or excessive iodine intake may lead to hypothyroidism and autoimmune thyroiditis.” (26) The high iodine causes inflammation of the thyroid gland and what is known as programed cell death. In other words, with the inflamed thyroid, cells start putting out signs of mass collapse, to which the body responds by sending out, antibodies in an attempt to deal with the damaged cells (27). This triggers an autoimmune reaction where the antibodies overextend their work and attack healthy thyroid cells.

Long-term excess iodine can also lead to thyroid cancer (28, 29, 30). You may not see any manifestation for years, even a decade, of excess iodine consumption, though a goiter may be the first sign that you have a problem.

Testing to really know

The Iodine Project determines the need for iodine by using a test known as the 24-hour urine iodine load test. It involves taking a high dose of iodine (50 milligrams) then collecting your urine for the next 24 hours. According to the advocates, if everything is fine and you have no iodine deficiency, then you will have urinated out all of the excess iodine during the 24 hours into the collection container. The problem is it is not so simple. In fact, this method can actually show people with high iodine to be deficient. Advocates of this test assert that 90% of the population is iodine deficient, but in reality, the science shows 89% of the US population to be iodine sufficient (31). So, this test falsely creates a picture that everyone needs more iodine.

Here is how it really is. The iodine load test assumes that all of the ingested iodine is actually absorbed, and this is not true. Not everyone has great absorption, to start with. And then, 14% of the US population has renal disease (32, 33, 34), which would skew the test. But the real plight is that ingesting a high amount of iodine causes the body to block absorption, such that a considerable amount is excreted in the feces, where it never could reach the kidneys to be urinated out in the first place and invalidates the test (35). Not to mention sweating some of the iodine out in this 24-hour period could affect the outcome. The bottom line is that the 24-hour urine iodine loading test does not reflect true iodine status (36).

So, how do you find out if you are iodine deficient? Most doctors run a group of tests called a thyroid panel, which determines if your thyroid is working properly. The basic panel often includes thyroid stimulating hormone (TSH), free T4 and free T3. Chances are if you are getting enough nutrients, including iodine, your thyroid should be operating optimally. I would add a serum iodine test to the thyroid panel, which can determine your iodine status. And yes, it has been shown to be accurate (37). Now, the advocates of the Iodine Project will argue a serum iodine is not an accurate test, because it shows people on this regimen to actually be dangerously high in iodine.

Iodine and the gut

Let’s return to the issue of ingested iodine being only partially absorbed and later found in the stool. The fact is that the more iodine you ingest, the less iodine you absorb (38). This means it must go through your digestive tract, where it is in contact with your gut microbiome. The gut microbiome is the collection of bacteria, yeast and fungi that live in the digestive tract that influence our digestion and ultimately our health.

Hospitals use iodine as an antiseptic, because of its antibacterial properties (39). Thus, when you ingest excess iodine, your beneficial bacteria are subject to attack, which may lead to dysbiosis (an imbalance of your gut microbes). Or your gut can become vulnerable to opportunistic bacteria and pathogens because the beneficial bacteria are not there to ward off these attackers. We know that with excess iodine you can have gastrointestinal upset, and even diarrhea (20), which affects your gut microbiota and ultimately your health.

In the colon, most of our beneficial bacteria live in the mucosal lining. High amounts of iodine can irritate the mucosal lining, affecting both digestion and absorption (40). The irritation produces an abundance of thinner and more viscous mucus, diluting the existing mucus and, in this case, acting as an expectorant (41), which allows for unwanted elimination of the mucus. With a thinning and reduction in the mucosa layer of the intestines, it will allow items that would normally be kept out of our bodies to permeate the intestinal wall and cause problems. It can again affect the beneficial bacteria and the abundance of the microbiome. Iodine’s full effect on the gastrointestinal lining and the colon’s microbiome has yet to be seen.

Iodine and hormones

One thing we are hearing more about these days is how some men seem to have less testosterone than they need. Excess iodine does not help in this regard, as it has been shown to reduce circulating testosterone (42). I have heard that one doctor calls iodine “the testosterone killer.” And high amounts of iodine can lower semen count as well (43), affecting both vitality and fertility (44). In women, iodine can adversely affect pregnancy, such that one study says, “even a little [iodine] excess is too much” (45). High iodine intake for health just doesn’t make sense.

We live in a “more is better” world. But in reality, too much of a good thing can be harmful, and in the case of iodine, there is a sweet spot. Too little is not a good thing, but neither is too much.

What to do…

While it’s important to get the iodine you need, I caution you not to overdo it. A little seaweed now and again will ensure iodine sufficiency, and even less kelp (which is very high in iodine). To give you a sense of it, just one gram of dulse seaweed or three-tenths of a gram of kelp per day give you all the iodine you need. That’s less than a teaspoon for dulse flakes, and even far less for the kelp … not very much at all. You can also have a little more, just not daily. Use it as a seasoning or as part of a weekly salad.

I don’t suggest consuming any iodized salt; it just isn’t good for you (4, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17). And you don’t need to take an iodine supplement; just get it from your food. Once again, too much iodine has been shown to be toxic, and it is easier to overdo it with just a pill (46, 47).

The chosen supplement of the Iodine Project is Lugol’s, and it has been shown to be toxic in excess (48). There may be some iodine in your foods, but the USDA and other nutrient trackers don’t assess iodine in foods, because they think everyone is ingesting iodized salt. This leaves us a little unsure. Just get a little seaweed now and again, and you should have no problem. Just don’t overdo it. This is where testing your thyroid function and testing for serum iodine levels to insure everything is optimal can really help.

Finally, don’t forget a good diet with lots of fresh fruits and veggies, which also provides all the other nutrient needs for good health. I think we can all agree that nutrient-deficient processed foods are not good for our health, and that goes for your thyroid health as well. Whole plant foods, on the other hand, give us a ton of nutrients far beyond iodine alone, which help maintain both thyroid health and general health.

The antioxidants in fruits and vegetables have been shown to increase thyroid health (49, 50, 51). The phytonutrients “(plant nutrients)” in fruits and vegetables also help thyroid function (52), including flavonoids which are particularly beneficial (53, 54). Then there are forgotten nutrients that the thyroid needs in addition to iodine, like sulfates (55, 56) and selenium (57, 58). You can find sulfates in several leafy green vegetables, especially the cruciferous ones, and selenium is abundant in Brazil nuts and sunflower seeds, just for starters.

All in all, a little common sense is in order. Neither excess vitamin supplements nor excess iodine accomplish what people hope they will, and in fact they can be quite harmful. Just focus on a plant-exclusive diet, which can create a far healthier thyroid than just overdoing one nutrient.


(2) Iodine Biofortification of Vegetables Could Improve Iodine Supplementation Status

(3) History of U.S. Iodine Fortification and Supplementation

(4) Increased Incidence Rate of Hypothyroidism After Iodine Fortification in Denmark: A 20-Year Perspective Population-Based Study

(5) Effect of Excess Iodine on Oxidative Stress Markers, Steroidogenic-Enzyme Activities, Testicular Morphology, and functions in Adult Male Rats

(6) The Relationship Between Thyroid Hormones, Antithyroid Antibodies, Anti-Tissue Transglutaminase and Anti-Gliadin Antibodies In Patients With Hashimoto’s Thyroiditis

(7) The Relationship Between Autoimmune Thyroid Disease and Iodine Intake: A Review

(9) Daily Salt Intake is Associated with Leg Edema and Nocturnal Urinary Volume in Elderly Men

(10) Dietary Salt Intake and Stroke

(11) Sodium Intake and Heart Failure

(12) Salt Intake, Hypertension, and Osteoporosis

(13) Excessive Salt Consumption Causes Systematic Calcium Mishandling and Worsens Microarchitecture and Strength of Long Bones in Rats

(14) Review of Salt Consumption and Stomach Cancer Risk: Epidemiological and Biological Evidence

(15) Salt Intake and Kidney Disease

(16) The Potential Role of Salt Abuse on the Risk for Kidney Stone Formation

(19) Table 1 Dietary Reference Intakes for Iodine by Life Stage Group

(21) A Review of Iodine Toxicity Reports

(22) Iodine-induced Thyroid Dysfunction

(23) Iodine-induced Hyperthyroidism: Occurrence and Epidemiology

(24) Iodine Excess and Hyperthyroidism

(25) The Relationship Between Autoimmune Thyroid Disease and Iodine Intake: A Review

(26) Effect of Iodine Intake on Thyroid Diseases in China

(27) Excessive Iodine Promotes Pyroptosis of Thyroid Follicular Epithelial Cells in Hashimoto’s Thyroiditis Through the ROS-NF-kB-NLRP3 Pathway

(28) Strong Association of High Urinary Iodine with Thyroid Nodule and Pupillary Thyroid Cancer

(29) Changing Patterns of Thyroid Carcinoma

(30) Nutritional and Environmental Factors in Thyroid Carcinogenesis

(31) Iodine Deficiency in 2007: Global Progress Since 2003

(32) Kidney Disease Statistics for the United States

(33) The Urinary Excretion and Thyroid Uptake of Iodine in Renal Disease

(34) Reversable Primary Hypothyroidism and Elevated Serum Iodine Level in Patients with Renal Disfunction

(36) Evaluation of the Iodine Loading Test: Urine Iodine Excretion Kinetics after Consumption of 50 mg Iodine/Iodide

(37) Use of Plasma Iodine Assay for Diagnosing Thyroid Disorders

(38) Dietary Iodide Controls its Own Absorption Through Post-Transcriptional Regulation of the Intestinal Na+/I- Symporter

(39) Benefit and Harm of Iodine in Wound Care: a Systematic Review

(40) Gastric Mucosal Changes Caused by Lugol’s Iodine Solution Spray: Endoscopic Features of 64 Cases on Screening Esophagogastroduodenoscopy

(41) Iodine-Induced Hypothyroidism and its Effect on the Severity of Asthma

(42) Effect of Excess Iodine on Oxidative Stress Markers, Steroidogenic-Enzyme Activities, Testicular Morphology, and Functions in Adult Male Rats

(43) The Association Between Iodine Intake and Semen Quality Among Fertile Men in China

(44) Iodine and Fertility: Do We Know Enough?

(45) Iodine Intake in Pregnancy – Even a Little Excess is Too Much

(46) Consequences of Excess Iodine

(47) Effects of increased Iodine Intake on Thyroid Disorders

(49) Oxidative Stress in Hypothyroid Patients and the Role of Antioxidant Supplementation

(50) Thyroid Hormones, Oxidative Stress, and Inflammation

(51) The Effect of Raw Vegetable and Fruit intake on Thyroid Cancer Risk Among Women: A Case-Control Study in South Korea

(52) Effects of Phytochemicals on Thyroid Function and Their Possible Role in Thyroid Disease

(53) Impact of Flavonoids on Thyroid Function

(54) Flavonoids and Thyroid Function

(55) Role of Sulfation in Thyroid Hormone Metabolism

(56) Sulfonated Tyrosines of Thyroglobulin are Involved in Thyroid Hormone Synthesis

(57) The Role of Selenium in Thyroid Hormone Metabolism and the Effects of Selenium Deficiency on Thyroid Hormone and Iodine Metabolism,'%2D5%20triiodothyronine%20(T3).

(58) Selenium and Thyroid Disease: From Pathophysiology to Treatment

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