Iodine Explained

Introduction

You may know of iodine as an element on the periodic table with the symbol I and the atomic number 53. It’s also a really important chemical element for proper functioning of the metabolism. As discussed in our Minerals article, iodine forms part of a number of essential elements. This means it’s necessary for a living organism to survive, but it cannot be made by the body and, therefore, must be ingested through our diet and/or supplementation. 

To drill down more into what Iodine is, iodine is a trace element, which means it’s only present in really tiny amounts. Only minute quantities are needed for normal bodily functions, and yet, there are a number of factors that can result in you having too much or too little. Like Goldilocks, we’re going to explain everything you want to know about iodine.

There’s loads to get into, but if you’d prefer to watch a brief video on what iodine is and what it does in the human body, watch this video:

Before we continue, it’s also worth pointing out that while there are many applications of iodine, particularly in medicine, we’re going to focus specifically on the metabolic functions of iodine.

Functions of Iodine

Iodine is an essential component of hormones produced in the thyroid gland. Without iodine, the body can’t make the growth-regulating hormones called triiodothyronine (T3), and thyroxine (T4). Hormones produced in the thyroid gland are essential for regulating our metabolism. 

A simple definition of metabolism is a chemical reaction in the body that changes food into energy. Thyroid hormones are responsible for regulating biochemical reactions in the body, healthy growth and development, and even things like body temperature and heart rate. 

Iodine is there for necessary for creating enzymes for these reactions, for synthesizing proteins, as well as for a healthy skeletal system and properly functioning nervous system. As you can guess, these are especially important in fetal development. 

Understanding Iodine uptake

In a healthily functioning body, iodine is taken up on an “as-needed” basis. The pituitary gland in the brain is a pea-sized gland responsible for regulating the endocrine or hormone system. The pituitary gland releases a chemical called thyroid-stimulating hormone (TSH or thyrotropin) to control the amount of thyroid hormones the thyroid gland makes. It carefully balances this system to prevent hypothyroidism and hyperthyroidism – more on this below.

When the pituitary gland secretes more TSH, it stimulates the thyroid gland to take up iodine and create T3 and T4. And this is where your levels of iodine come in. If your body is creating TSH, but there is insufficient iodine in your body, you can develop a condition called goiter. But we’ll get into the disorders further down. On the flip side, if your body has sufficient amounts of T3 and T4 to regulate your metabolism well, the pituitary gland does not make TSH, and the iodine in your body is not used up.

Recommended Amounts of Iodine

Since it’s necessary to get iodine from your diet or through supplementation, research suggests that the daily allowance for iodine in adult men and women is 150 micrograms (mcg of μg). For pregnant or lactating women, this should increase to between 220 and 290 mcg per day.   Here’s some more detail:

• Adult male (19< years): 150 mcg
• Adult women (19< years): 150 mcg
• Pregnant woman: 220 mcg
• Breastfeeding woman: 290 mcg
• Babies up to 12 months: 110 – 130 mcg
• Children up to 8: 90 mcg
• Children up to 13: 130 mcg

If you’re wondering what these amounts look like in the form of food, they can vary widely. This is because iodine can be found naturally in a wide range of food sources (more on this below), but also because it’s often added to foods to fortify them. As an example, just 1 gram of iodized salt contains 77 mcg or 55% of your recommended daily allowance (RDA). And, if you love dried seaweed, it’s possible to get well over 1000% of your RDA, depending on the species of seaweed and brand of product.

So as you can see, iodine really is a trace element. Most research suggests that the minimum amount your body needs to function can be as little as 70 mcg of iodine per day. The higher figures stated above are more for optimal functioning of certain systems, such as lactation, mucus in the digestive system, salivary glands, brain cells, and the walls of your arteries. Therefore, in most cases, it’s pretty easy to get your daily dose without the need for supplementation.

Signs and Symptoms of Iodine Deficiency

As we mentioned earlier, if there’s a deficiency of iodine in your body, it affects the production of T3 and T4. The body responds by swelling the thyroid gland, where these hormones are made in an attempt to try and take up the necessary iodine and reverse the existing hypothyroidism. This condition is called goiter. Depending on the severity, it is categorized into Class I, II, or III. In the image below, this is Class I, while the most severe goiter would be class III and significantly larger. 

The deficiency of iodine affects two billion people around the world. These are mostly in poor, developing countries that are inland and typically semi-arid. This is why basics, like salt, are often fortified with iodine.

Understanding Hypothyroidism

The easiest way to remember what this condition is, is by remembering the Latin prefix hypo meaning “below” or “under”. Think about other words where you’ve heard it, like hypothermia or being dangerously cold, or hypoglycemia, when your blood sugar is too low.

Hypothyroidism is the opposite of hyperthyroidism and it means your thyroid gland is underactive. There is not enough T3 and T4 being produced by the thyroid gland, and so your body has difficulty managing the metabolism. Because your body is running more slowly, you’ll experience symptoms like:

• Feeling tired and lethargic
• Weight gain
• Feeling depressed
• Feeling sensitive to the cold
• Dry hair, skin, and nails
• Aching muscles

Hypothyroidism can be caused by a lack of iodine in the body, but also by congenital conditions that will affect a child’s growth and development, by conditions like thyroid cancer or even following the removal of the thyroid gland for cancer treatment.

Understanding Hyperthyroidism

The easiest way to remember what this condition is, is by remembering the Latin prefix hyper, meaning “over” or “too much”. Think about other words where you’ve heard it, like hyperventilating, meaning you breathe too fast, hyperextending your finger when you accidentally bend it backward or being hypersensitive or overly sensitive to something.

Too much iodine in your body, or the body’s overuse of iodine, can result in a condition called hyperthyroidism or an overactive thyroid. As we explained earlier, the thyroid is necessary for producing two hormones T3 and T4, for regulating metabolism. If there is too much T3 and T4 in your body, then you’re likely to experience the following because your metabolism is overactive. It’s as though your body is continually in overdrive from drinking too much coffee…

• Feeling nervous, edgy, anxious, and irritable
• Diarrhea
• Mood swings
• Difficulty sleeping
• Irregular or fast heartbeat
• Twitching, shaking, trembling, or itchiness
• Weightloss
• Excessive thirst and urination
• Changes to your sexual appetite
• Feeling sensitivity to heat
• Bulging eyes

In cases of hyperthyroidism, a condition known as exophthalmos can occur. This is when one or both eyes begin to bulge out of the eye socket.

Signs and Symptoms of Iodine Toxicity

Through research, it’s been established that the upper intake level of iodine in adults is around 1,100 mcg per day. Under this amount is unlikely to cause any adverse effects. So what happens when this upper limit is exceeded? Then it’s possible to develop acute or chronic toxicity ranging from mild to severe. In mild cases, toxicity can manifest through symptoms such as upset stomach, nausea, vomiting, and diarrhea.

In severe cases, too much iodine can cause the thyroid gland to become dysfunctional and can lead to conditions like:

• Thyroiditis: Swelling or inflammation of the thyroid gland.
• Hypothyroidism: Insufficient thyroid hormone is produced by the body.
• Hyperthyroidism: Too much thyroid hormone is produced by the body.
• Thyroid papillary cancer: the most common type of thyroid cancer. They are small growths and can be treated effectively.

It’s worth noting, however, that elemental iodine, which is often used in a medical setting for disinfecting, is toxic and should not be ingested undiluted. Just 2 grams of this could induce toxicity and be fatal for an adult weighing between 70 and 80 kgs. 

Food Sources for Iodine

Fortunately, it’s pretty easy to consume enough iodine through your diet, and it’s not necessary to take a supplement. In fact, in a study in the year 2000, it was found that the average intake of iodine in American men was 240-300 mcg/day and in American women was 190-210 mcg/day. In a 2015 study in Japan, which has a diet rich in fish, seafood, and seaweed, adults consumed between 1,000 and 3,000 mcg/day

The most common sources of dietary iodine include fish and seafood, dairy products, eggs, and iodized salt. This can prove a challenge for vegetarians and vegans, but there are also lots of plant-based products like soya milk or oat milk that’s been fortified with iodine, or seaweed and kelp that have naturally high levels of iodine. 

Further Reading: Vitamin B1 Explained

References

Goiter images: https://en.wikipedia.org/wiki/Goitre#/media/File:Struma_001.jpg

Iodine toxicity: https://pubmed.ncbi.nlm.nih.gov/32809605/

Exophthalmos https://en.wikipedia.org/wiki/Exophthalmos#/media/File:406907P-PA-OCULAR.jpg 
https://ods.od.nih.gov/factsheets/Iodine-HealthProfessional/#:~:text=Iodine%20is%20a%20trace%20element,)%20and%20triiodothyronine%20(T3).