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Iodine is an element which is an essential micronutrient. Iodine is needed to produce thyroid hormones, which play an important role in metabolism and thermoregulation. Iodine deficiency has a significant effect on the thyroid, as well as on one's general health. Severe iodine deficiency may cause hypothyroidism, also known as an underactive thyroid.
Most people get enough iodine in their diet through consumption of iodized salt and other foods containing iodine. Most commercially available table salts, which are used in cooking and in some processed foods, are iodized, in other words, they are fortified with iodine.
Certain people are at an increased risk for iodine deficiency, although iodine deficiencies are uncommon in North America. Pregnant women, vegans, and those who avoid iodized salt may be at increased risk of iodine deficiency.
Iodine and thyroid health: what’s the link?
When a person is deficient in iodine, their body cannot make thyroid hormones. Not having enough thyroid hormones is called hypothyroidism.
Thyroid hormones play many important roles in the body, including thermoregulation, growth and metabolism. In response to the lack of thyroid hormones, the body increases secretion of TSH (thyroid stimulating hormone), a hormone which stimulates the thyroid to make thyroid hormones. But because there is not enough iodine available to make thyroid hormones, a feedback loop occurs as the body continues to increase the amount of thyroid stimulating hormone.
If you're unsure if you have an overactive or underactive thyroid, it's always best to test your TSH levels.
A goiter is an enlarged thyroid, which looks like a large swollen area in the neck. In cases of severe iodine deficiency, the thyroid can become enlarged from elevated TSH, causing a goiter. The most common cause of a goiter, worldwide, is iodine deficiency. A goiter is one of the telltale signs of serious iodine deficiency, and if you suspect you have one, you should speak to a healthcare provider.
Who is at risk of iodine deficiency?
Although iodine deficiency is uncommon in North America, some people are at an increased risk. According to the National Institutes of Health Office of Dietary Supplements, certain groups are more likely to be deficient in iodine such as:
- People who avoid iodized salt or who use sea salt instead - Unprocessed sea salt does not contain iodine, so if you use this kind of salt at home and cook all of your own food, you may be at an increased risk of iodine deficiency.
- People who follow a vegan diet - Dairy products, eggs, and seafood are very good sources of iodine. Avoiding these foods may reduce the amount of iodine in the diet.
- Pregnant and lactating women - Pregnant women need around 50% more iodine to support the growing baby. Many prenatal supplements contain iodine. However, excess iodine exposure might be detrimental as well.
- People who get marginal levels of iodine, but who eat goitrogenic foods - Goitrogens are foods that disrupt thyroid hormone production by interfering with iodine uptake or by preventing iodine from binding to proteins used to form thyroid hormones. These are found in some plant-based foods, including cruciferous vegetables like broccoli, cabbage, cauliflower, and kale, as well as in soy. This is another reason why those following a vegan diet could be at risk.
How much iodine do you need?
The recommended daily intake for iodine varies by age and pregnancy status:
The average recommended daily intake for adults is 150 micrograms per day. Over time, a consistent intake of less than 50 micrograms per day may cause hypothyroidism and the development of a goiter.
In the times before modern agriculture, we got enough iodine from the soil our food was grown in. These days, many soils are depleted of iodine. Because of this, entire geographical regions have become devoid of iodine, and their populations vulnerable to deficiency. This is what led to the widespread practice of iodizing table salt, and using this salt is enough for most people to maintain healthy thyroid function.
Dietary sources of iodine
The best dietary sources of iodine are:
- Iodized table salt
- Dairy products, including cows milk, cheese, and yogurt
- Saltwater fish, including tuna and cod
- Seaweed, including nori, kelp, and kombu
- Eggs
If you are concerned that you may be deficient in iodine, the first step is to ensure you are using iodized table salt. Next, check your multivitamin’s label. Many multivitamins are fortified with iodine.
If you have symptoms of hypothyroidism, or a goiter (swollen thyroid in the neck area), speak to your healthcare provider.
Importance of iodine during pregnancy and breastfeeding
Women require higher levels of thyroid hormone during pregnancy, which means -- you guessed it -- they require more iodine during pregnancy too. They also require more iodine while breastfeeding.
Most prenatal vitamins contain enough iodine to meet the daily requirements for pregnancy. If you are concerned that you may not be getting enough iodine during pregnancy or lactation, try incorporating high-iodine foods into your diet regularly.
There are risks associated with being deficient in iodine while pregnant or lactating. According to the National Institutes of Health Office of Dietary Supplements:
“In pregnant women, severe iodine deficiency can permanently harm the fetus by causing stunted growth, intellectual disability, and delayed sexual development. Less severe iodine deficiency can cause lower-than-average IQ in infants and children and decrease adults’ ability to work and think clearly.”
Read more in our guide to hypothyroidism and pregnancy.
Taking too much iodine
Finally, remember that there are risks also for excessive intakes of iodine. In fact, too much daily iodine can produce the same symptoms as iodine deficiency, by inhibiting the thyroid gland. Very high intake can cause inflammation of the thyroid, or even thyroid cancer. Currently, it is recommended that no one exceeds an intake of 1100 mcg of iodine per day.
People who have moved from regions with low iodine intake in the diet (e.g. some European countries) to a region with adequate iodine intake (e.g. the USA) can actually develop thyroid problems. The body adapts to its environment, and the thyroids of people in low-iodine regions can become good at using very small amounts of iodine. When the level of iodine suddenly increases, the body may end up with excessive iodine.
Dr S. Guandalini, MD, Professor Emeritus of Pediatrics at University of Chicago Medicine suggests that a possible way to slowly increase your iodine intake if you are using only sea salt, is to progressively replace sea salt with iodized salt over a period of 3-4 months. However, it is always a good idea to seek advice from your personal physician before changing your diet.
Final thoughts
Iodine is important for healthy thyroid functioning because it is required for the body to manufacture thyroid hormone. When a person is deficient in iodine, they may experience symptoms of hypothyroidism, and may also experience a goiter, a swollen thyroid gland in the neck caused by elevated TSH.
Most North Americans get enough iodine in their diet by consuming iodized salt. Other dietary sources of iodine include fish, eggs, dairy, and seaweed. Pregnant and lactating women, vegans, and those who avoid table salt may be at an increased risk for iodine deficiency. Getting enough iodine is especially important during pregnancy and lactation.
If you are concerned that you are deficient in iodine, it’s a good idea to speak to your healthcare provider.
