Importance of iodine for thyroid and general health
Nov 30, 2025ir. Yvana van den HorkMood, Immunity & Wellness, Minerals, Inflammation, Cell replication, Nutrition, Anti-aging, Joints
Importance of iodine for thyroid and general health
In some ways, my partner and I are polar opposites. Until I became interested in fitness, it was easy for me to get so caught up in my activities that I regularly forgot to eat. Sometimes it would already be late at night.
This was often a big advantage during my more challenging bike rides, such as one across Cuba, because I could cover longer distances without having to lug cooking utensils around and worry about food.
How different the situation is for my partner. He practically faints if he doesn't eat a meal every 3-4 hours, which of course also means he'd spoon out half a container of soft cheese in the middle of the night.
In his case, there's a fairly logical explanation: his thyroid was overactive due to a hereditary autoimmune condition (Grave's), making it important to eat regularly. Ultimately, part of his thyroid was deactivated by means of radiation.
But he's maintained his regular eating habits ever since.
That's why a recent study published by Ergo-Log piqued my interest: Treatment of Graves' disease is more successful with an iodine-rich diet
A very strange conclusion, because people with an overactive thyroid are always told to avoid iodine, and suddenly (in a small study) it appears that a normal iodine intake actually produces better results!
That's why I thought it would be interesting to delve deeper into iodine-rich foods and thyroid function. Of course, almost all literature still recommends reducing iodine intake for overactive thyroids. In addition, more micronutrients are important for a healthy thyroid than I realized. Not only does vitamin D play a significant role, but even magnesium is essential for a healthy thyroid. You'll be able to read about that in a future article. In this article we focus exclusively on iodine as well as on the emergence of seaweed as a superfood.
How iodine deficiency increases your risk for chronic illnesses
Iodine is essential to your health. Unfortunately people don't consume nearly enough of it.
Many people don't know they need to consume a little iodine each day to maintain healthy levels of this essential micronutrient.
Unfortunately average iodine intake dropped in the past decades.
Your body uses iodine across several organ systems, but it is most commonly known to synthesize thyroid hormones that regulate nearly every bodily system. Several thyroid hormones secreted by your thyroid gland are transported throughout your body where they control your metabolism and energy production.
This means that every cell in your body depends on the production and function of thyroid hormones. Your thyroid gland is under the control of your pituitary gland that is located at the base of your brain. In turn, the pituitary gland is under the control of your hypothalamus. In other words, there are several steps needed to identify low thyroid hormone levels and to tell your thyroid gland to begin secreting more.
Milk substitutes are low in iodine
Iodine content was evaluated in 47 milk alternatives and compared to cow's milk. Researchers included almond, soy, coconut, rice and hazelnut milk alternatives, but excluded products marketed specifically for infant consumption.
They discovered the majority of brands did not have adequate levels of iodine as compared to cow's milk. Most contained only 2% of that found in cow's milk.
Only three milk alternatives were fortified with iodine. This means that opting for a milk alternative may increase your risk of developing an iodine deficiency, as the milk alternatives tested only provided 2 mcg per serving, while 2 glasses of cow's milk will cover your recommended dietary allowance (RDA) of iodine.
Statistically speaking, you may have difficulty absorbing milk products, which means you would have a negative reaction when you drink cow's milk. In the USA approximately 65% of all people have difficulty digesting lactose after infancy.
Lactose is the sugar found in cow's milk. This intolerance or allergic reaction to milk sugar is the reason some turn to milk alternatives.
However, many people are unaware of the need for this vital dietary mineral and it is important that people who consume milk-alternative drinks realize that they will not be replacing the iodine from cows’ milk which is the main UK source of iodine. This is particularly important for pregnant women and those planning a pregnancy.
A glass of a milk-alternative drink would only provide around 2 mcg of iodine which is a very small proportion of the adult recommended iodine intake of 150 mcg/day. In pregnancy, that recommendation goes up to 200 mcg/day.
Iodine, an essential micronutrient
Your thyroid hormones are essential for normal growth and development in children, neurological development in babies before birth and in the first year of life, and in regulating your metabolism.
Deficiency may be most damaging to the developing brain and could result in miscarriage, preterm birth or neurological impairment in a newborn.
Before moving forward, let's clarify the difference between iodine and iodide. Iodine is the molecule that is taken up by cells in the body. However, iodine is not very available in food and supplements.
Iodide, having greater stability, is the form typically found in supplements. In your body, the iodide molecule is converted into iodine, which is the active form needed by your thyroid gland.
The RDA is 150 mcg per day for adults, 220 mcg/day for pregnant women and 290 mcg/day for women who are breastfeeding.
However, most adults are not consuming enough iodine each day to meet the minimum levels required for health.
The World Health Organization (WHO) defined iodine deficiency in large populations as median urinary concentrations of 99 mcg/L or less.
These low levels of iodine would likely result in visible symptoms, such as a goiter (swelling of the thyroid gland), hypothyroidism or pregnancy-related problems.
More insidious are problems with subclinical deficiency, or levels that can't support optimal health but are not low enough to create immediate life-threatening problems.
Your risks of subclinical iodine deficiency
Risks of subclinical iodine deficiency are not limited to pregnancy and infant neurological development or weight gain. Nearly 2 billion people worldwide don't get enough iodine in their diet, and 50 million suffer from brain damage caused by the deficiency.
This may very well be the most preventable cause of brain damage in infants and children, and yet 36.5% of children are estimated to have an iodine deficiency.
Even a small deficiency in an adult's iodine level may reduce your IQ by up to 15 points,15 which may affect your ability to get a job and keep it. Subclinical iodine deficiency, also known as iodine deficiency disorder, is subtler than a goiter and may be more dangerous.
Iodine helps lower the risk for reductive stress that may lead to chronic diseases, such as diabetes, atherosclerosis and arthritis. When your thyroid is not fully functional it can also lead to heart disease. Other tissues in your body also use iodine in appreciable amounts, including:
Salivary glands : low levels of iodine may lead to dry mouth.
Skin : your body uses iodine in the development of skin, teeth, nails and bones. Low levels of iodine may lead to acne.
Eyes:iodine is an antioxidant that naturally protects your eyes against ultraviolet radiation.
Immune system : iodine is a scavenger of free hydroxyl radicals and stimulates the activity of other antioxidants.
Muscles: iodine deficiency may lead to pain, fibromyalgia and muscle weakness.
Pancreas: radioactive iodine therapy is a common therapy in thyroid cancer. Studies demonstrate that radioactive iodine is absorbed by the pancreas and predisposes you to glucose intolerance.
Stomach: iodine is used by the cells lining your stomach to concentrate chloride to produce hydrochloric acid used in the digestion of your food.
Iodine protects you against cancer
Iodine functions in a protective role against the growth of cancer cells. Although the exact mechanism is unknown, researchers have found that cancer cells shrink after injection with iodine and some die and are then replaced with healthy cells.
Iodine is also involved in apoptosis, or programmed cell death necessary for the development of new cells and removal of malignant or diseased cells.
The incidence of thyroid cancer has increased worldwide, driven in part by better screening that may pick up small benign tumors, which otherwise would not have caused a medical problem. However, this has also coincided in the USA with a reduction of iodine intake.
Some studies have suggested that prophylactic iodine in deficient populations may reduce the diagnosis of more aggressive forms of thyroid cancer.
Iodine is also vital to breast health in women who are breastfeeding and in older women. A deficiency may lead to fibrocystic disease or breast cancer. Human breast tissue and breast milk contain higher concentrations of iodine than your thyroid gland, as iodine is essential to the development of a newborn's brain.
However, it also plays an important role in the health of the breast tissue as it exerts a powerful antioxidant effect. Breast tissue deficient in iodine has elevated markers of lipid peroxidation, one of the early signs of cancer development.
Breast tissue that is iodine-deficient also demonstrates increases in estrogen receptor proteins and alterations in DNA.
When a woman's iodine levels are low, it stimulates the ovaries to produce more estrogen, which stimulates growth in breast tissue. Iodine also helps regulate cortisol, which is associated with a higher risk of breast cancer.
When you compare Japanese and Western diets against the incidence of cancers, these differences become even more apparent.
Breast cancer rates for women living in Japan and eating a diet high in iodine are 66% lower than for American women. However, once a Japanese woman moves to the USA, her breast cancer rate rises to the level of American women. Cells that line your stomach also capitalize on the antioxidant effects of iodine.
Those living in iodine-deficient populations have a higher incidence of goiters and stomach cancers. An increase in iodine intake has been strongly correlated with a reduction in the incidence of stomach cancer.
Iodine deficiency affects more women than men
Women are much more likely to develop symptoms of hypothyroidism.
According to different research, women are having problems with thyroid gland three to 10 times more than men. This also applies to toxic goiter and insufficiency of thyroid hormones.
In the USA, hypothyroidism disproportionately affects women more than men, likely because the female hormone estrogen inhibits the absorption of iodine, while testosterone may promote the absorption of iodine. Therefore, what little iodine you consume from your diet is absorbed and used differently based on your gender.
Hypothyroidism is associated with 80% to 90% free estrogen levels. This means the lack of iodine increases free estrogen levels that stimulate growth in breast tissue. The normal value of free estrogen is 40% to 60%. On the other hand, hyperthyroidism is associated with only 20% free estrogen.
The interplay of estrogen, thyroid hormone and iodine is a complex mechanism and increases a woman's risk of iodine deficiency.
Chemicals in your environment also block iodine absorption
While women have a greater incidence of iodine deficiency related to their hormone production, everyone experiences poor absorption and utilization related to environmental contamination. Some contaminants that compete with iodine include:
• Fluoride:fluoride is a halogen that has an atomic weight lighter than iodine and can grab receptor sites more easily, thus taking the place of iodine resulting in a deficiency in your thyroid, stomach cells, ovaries and other organs.
• Bromide:iodine used to be used in processing flour. However, manufacturers have replaced it with bromide, another halogen with a lower atomic weight than iodine. This switch effectively reduced your consumption of iodine and injected an element that competes with iodine in your body.
• Perchlorate: this is a contaminant found in the groundwater across the USA and in measurable amounts in milk, fruit and vegetables. In high doses, perchlorate may inhibit the function of your thyroid gland, but even in low doses, it inhibits the uptake of iodine by your thyroid gland, leading to hypothyroidism.
• Nitrates: this may interfere with the uptake of iodine in your thyroid. Avoid added nitrates you find in processed meats, such as luncheon meat, sausage, bacon, hot dogs and some packaged seafood.
• Mercury: there is evidence that iodine may help detoxify your body of toxic mercury, found in fish, dental amalgams and consumer products such as antiques, electronics, batteries, light bulbs and pharmaceutical products.
Iodine sources
Before the 1920s, some regions of the U.S. were known as the "goiter belt," as 26% to 70% of children suffered from goiter.
An iodine prophylaxis program was begun in Ohio in 1917 with over 2,100 schoolgirls. In the following years, the researchers found a significantly decreased frequency of goiter in the girls who received the iodine supplement over those who did not.
It wasn't until 1924, after a successful iodination program in Switzerland and spurred by a series of reports, that table salt was fortified with iodine. However, research has found varying degrees of iodine in salt labeled iodized, and 53% of the samples had much less iodine than was listed on the label.
Experts believe the declining levels of iodine in the US population may be the result of several factors, including:
- eating less salt in the mistaken belief that it is bad for your heart
- consuming more dairy substitutes low in iodine, such as almond, hazelnut or hemp milk
- snacking on junk foods that are not salted with iodized salt
- eating foods grown in iodine-depleted soil
- drinking less dairy, which is often a primary source of iodine
- eating little to no iodine-rich sea plants, such as kelp
Foods that contain higher amounts of iodine include sea vegetables, such as kelp, kombu and wakame.
Kelp has the highest amount of any food and just one serving gives you four times the RDA. You can read more about the restorative benefits of kelp in the next section.
Organic, grass fed butter is another source of iodine and healthy fats in your diet. Grass fed butter is also high in vitamins and lipids that are important to support your overall health.
Seaweed is the next superfood
In Asian households, seaweed is an integral part of daily meals. It’s added to soups, used as a salad ingredient, served as a side dish, and even dried and eaten as a crunchy snack. In Japan, around 21 types of seaweed are used in cooking, six of which have been used as far back as the 8th century.
Seaweed isn’t just versatile and delicious, but healthy as well. And the good news is Westerners are catching up and taking notice of this marine delicacy, hailing it as the next superfood.
Kelp seaweed could be the next rising superfood. The prevalence of kelp seaweed in new products across Europe increased from 2005 to 2023, and is expected to grow further in the oncoming years.
The health and sustainability benefits that kelp seaweed offers are the primary reasons why there’s a growing interest in algae today.
Seaweed has already gained popularity in western cuisine as chefs and food manufacturers explore its unique flavors and nutritional value. Food and drink brands have the potential to explore greater options with kelp.
For example, in the snack category, creating seaweed-infused crispy seaweed chips or mixing seaweed into already popular items such as crackers or popcorn. Manufacturers can make seaweed more approachable for consumers and enhance its adoption by presenting it in familiar formats.
Kelp and other seaweeds are abundant in nutrients
Kelp is a variety of seaweed that grows in vast seabeds in coastal regions all over the world. It’s also called brown algae and thrives mostly in cold, nutrient-rich waters.
Commonly described as a foundation species, kelp creates forest-like habitats fostering huge and diverse amounts of life, including sea snails, brittle stars, lobsters, various species of fish, seals, sea otters and more.
Kelp forests are found along 25% to 30% of the world’s coastlines, making them the most extensive marine-vegetated ecosystems in the world. They are predominantly cool water species and can be found in temperate, Arctic and sub-Antarctic areas. Some of the largest forests are located along the California and Pacific Northwest coastlines, up to and including Canada and Alaska.
Kelp has been dubbed a marine superfood, and its potential health benefits will potentially attract the interest of wellness-minded consumers, prompting the food industry to incorporate it into their products.
Indeed, kelp and other types of seaweed — nori, kombu and wakame, to name a few — are nutritionally diverse, offering a wide array of nutrients that can provide whole-body benefits.
Seaweeds offer:
- Vitamins A, C, D, E and K
- essential minerals like calcium, iron, iodine, magnesium, phosphorus, potassium, zinc, copper, manganese and selenium
- B vitamins (B1, B2, B9 and B12)
- protein and essential amino acids
- anti-inflammatory polyphenols
- dietary fiber
Seaweed is also rich in arginine, glycine, alanine and glutamic acid, and contains all the essential amino acids. It has dietary fiber, which is essential for digestive health.
The iron in seaweed helps with healthy blood formation and may prevent anemia, while the polyphenols help fight free radicals. These functions help ensure the growth of strong bones and optimal muscle function.
Consumption of kelp seaweed has been linked to the improvement of sensory receptors, promoting healthy blood vessels, aiding in digestion and weight management and even reducing hair loss. Just be mindful of your portions if you already have high iron levels.
Seaweed plays a role in the lives of Japanese centenarians
Japan has one of the highest centenarian populations. Most of them live in Okinawa, an island that’s been dubbed as a "Blue Zone" of longevity.
While many factors contribute to their long lives, such as being stress-free and appreciating day-to-day pleasures, one specific aspect that’s been considered is their nourishing diet composed of farm-to-table ingredients, with seaweed as one of the foundational components.
In particular, fucoidans, a powerful polysaccharide found in some types of seaweed including kelp, has been identified to provide anti-aging and immune-boosting effects. Fucoidans make up 25% to 30% of seaweed’s dry weight, depending on the type and the season.
They present biological activities such as:
- antibacterial
- antiviral
- anti-inflammatory
- anticoagulant
- antithrombotic
- antidiabetic
- procoagulant
- anticancer
It has been shown that fucoidan-rich Undaria, once ingested, can bind to toxins such as dioxin within the mammalian body and facilitate its excretion.
The effect is noteworthy enough that some clinicians believe it could hold promise as a therapeutic intervention in humans exposed to dioxin.
Laboratory and animal studies further reveal that fucoidans prevent certain infectious diseases, and block cancer cells from spreading and trigger their early death.
Seaweeds may have potent antiviral capabilities
The potent antiviral properties of seaweeds have also been demonstrated in several studies. One study that used extracts from six brown seaweed species from Hong Kong found that they inhibited herpes simplex virus types 1 and 2, with very low toxicity to other cells.
Another study found that polysaccharides from red and brown seaweeds prevented the viral replication of the hepatitis C virus.
More recently, in 2020, a study found that seaweed extracts exhibited promising results against SARS-CoV-2. The extracts used a decoy technique, which has been found effective against other viruses like Zika, dengue and influenza A.
As explained in Science Daily:
"The spike protein on the surface of SARS-CoV-2 latches onto the ACE-2 receptor, a molecule on the surface of human cells. Once secured, the virus inserts its own genetic material into the cell, hijacking the cellular machinery to produce replica viruses.
But the virus could just as easily be persuaded to lock onto a decoy molecule that offers a similar fit. The neutralized virus would be trapped and eventually degrade naturally."
What else can seaweeds do for you?
Seaweed’s superfood status is further supported by its many potential advantages for human health, as well as its sustainability. It’s regenerative — it does not require herbicides, pesticides, feed, irrigation and land to grow, making it one of the best zero-input crops today.
You can consume kelp and most varieties of seaweed raw, cooked and added into foods or served as a side dish or salad, or chopped in bits and added as a topping to your meals. Kelp supplements are also available today. Whatever form you choose, here are more potential benefits you can reap from this marine vegetable:
1 May help lower your risk of cardiovascular events: a study found an inverse association between seaweed consumption and total stroke risk among Japanese men. Another study noted that the polyphenol content of seaweed may be the reason for its cardioprotective benefits.
2 Promotes thyroid health: iodine deficiency is a growing concern today, which can pose a problem, as this nutrient is essential for proper thyroid hormone production.
You cannot make iodine in your body; you need to get it from the foods you eat. Kelp is one of the top sources of iodine, and just a small amount can help you meet the recommended daily amounts.
However, remember that you only need small doses of iodine. You need to balance your levels, as too much or too little can lead to either hypo- or hyperthyroidism.
3 May help manage diabetes: the alginic acid in seaweed is known for its positive effects on diabetes and blood coagulation. A 2011 study found that kombu specifically has antihyperglycemic effects that may help reduce the risk of obesity and diabetes.
4 May help promote brain health: glutamic acid in dulse, which becomes glutamate in your body, is essential to your nervous system and may positively influence your memory, learning, cognition and normal brain function.
Astaxanthin, another marine superfood
Macroalgae like seaweeds can offer impressive benefits, however, don’t miss out on the benefits of microalgae as well. In particular, the green microalgae Haematococcus pluvialis contains the potent carotenoid astaxanthin, which can have tremendous advantages for your health.
Astaxanthin provides protection against reactive oxygen species and oxidation, which play a role in aging, cardiovascular disease, Alzheimer's disease and Parkinson's disease.
It may be called the "king of antioxidants," as it may be more potent compared to other antioxidants like vitamin A, vitamin E and lycopene. Although it’s related to beta-carotene, lutein and canthaxanthin, it has a unique molecular structure that sets it apart from other carotenoids.
Astaxanthin is available in supplement form. If you decide to give it a try, it is recommended to start with 4 mg per day, and working your way up to about 8 mg per day — or more if you're an athlete or suffering from chronic inflammation. Taking this supplement with a small amount of healthy fat, such as butter or organic pastured eggs, will optimize its absorption.
The whole-body benefits of astaxanthin are so impressive, which is why this is one of the top antioxidants.
Some advice before you load up on kelp and other seaweeds
Going back to kelp and other seaweeds. While the benefits are promising, remember that you must be aware that they contain certain ingredients that, if consumed in excessive quantities, can have repercussions for your health.
For example, most seaweeds contain polyunsaturated fatty acids (PUFAs), including linoleic acid, which can be harmful to your health in excessive amounts. It’s best to limit your LA consumption to 5 grams, or even better, 2 grams a day to protect your health.
Seaweed also contains some amounts of fluoride, which is a known neurotoxin that can lead to developmental problems in infants and young children, including mental difficulties and IQ reduction.
If you only consume small amounts of seaweed, however, the quantities will be too tiny to produce any drastic, long-lasting effect.
Be wise with your seaweed choices. You may be tempted to munch on products like dried laver seaweed sheets, for example, but these can be seasoned with artificial flavorings and vegetable oils like sesame oil, which can add to your LA burden. As much as possible, opt for plain, unseasoned kelp and seaweed products.
Red seaweed varieties (Eucheuma, Chondrus, Hypnea and Gigartina) also contain carrageenan. In its natural form, carrageenan has nutritional value and has even been noted to have anticancer potential. However, this hydrocolloid, when used in food processing, undergoes an extensive treatment and extraction process that changes its chemistry, turning it into an ultraprocessed, synthetic ingredient.
As a result, carrageenan in food products has been linked to certain adverse effects, such as gastrointestinal disorders and tumor formation in animal studies due to its potential to trigger inflammatory pathways. The natural carrageenan in fresh seaweed likely wouldn’t cause any harm, but keep an eye out for the synthetic version — it’s mostly found in processed foods like pasteurized dairy, deli meats and canned soups.
Summary
Iodine is an essential micronutrient crucial for thyroid hormone production, metabolism, brain development, cancer protection (especially breast and stomach), and overall health.
Modern diets (low dairy, milk alternatives, reduced iodized salt, iodine-depleted soil) have led to widespread subclinical deficiency, affecting billions and linked to hypothyroidism, cognitive decline, and chronic disease.
Contrary to traditional advice to avoid iodine in hyperthyroidism (e.g., Graves’ disease), emerging (small) studies suggest normal iodine intake may improve treatment outcomes.
Seaweed (especially kelp, kombu, wakame) is the richest natural source and is gaining recognition as a sustainable superfood with anti-inflammatory, antiviral, anticancer, and longevity-promoting properties.
However, moderation is key due to potential excess iodine, heavy metals, fluoride, or PUFAs in some products.
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