What you need to know about iodine

Don’t know much about iodine? Read on.

Iodine is a trace mineral nutrient. The recommended intake is listed in micrograms (one millionth of a gram), ranging from 90 mcg for a young child to 150 mcg for an adult.

We get iodine from a limited number of foods.

  • Dairy foods: iodine content of milk and dairy products depends on whether the dairy animal consumed much iodine from its diet or from supplements.
  • Sea vegetables: seaweed and other ocean plant foods may contain iodine. Some of these have so much iodine, they could produce toxicity if eaten in large amounts. With others, the iodine may not be bioavailable, because other components of the plant block absorption.
  • Iodized salt: Salt itself is not a natural source of iodine. In the U.S., iodized table salt has been available since the 1920s. 1/4 teaspoon of iodized table salt (1.5 grams) contains about half an adult’s daily iodine recommendation. But not all salt is iodized. Shoppers can choose non-iodized salt. Food manufacturers do not typically use iodized salt in food processing. Speciality salts like kosher, Himalayan and sea salt are not typically iodized.

Ocean fish and foods prepared at home with iodized salt may include significant iodine. For example, the iodine content of pasta is improved by adding iodized salt to the cooking water. Other foods may contain some iodine, but the amount will vary according to how much iodine was in the soil where the food was grown.

Here’s the main problem with assessing iodine intake: the iodine content of foods is unpredictable and variable. The only food with a reliably consistent iodine content is iodized table salt. Foods may contain a little, a lot, or they may have a reasonable amount. Sort of like Goldilocks and the 3 Bears. The problem is, unlike Goldilocks, we can’t tell which foods are “just right” for iodine from tasting them.

Thyroid Function

Iodine is a critical component of thyroid hormones. Without adequate iodine intake, the thyroid gland –located in the neck — cannot make enough thyroid hormone. In parts of the world where the soil has little iodine, people develop iodine deficiency. In response to inadequate iodine, the thyroid gland grows excessively, bulging out of the neck. This condition is called goiter.

Certain foods contain substances called goitrogens, which actually interfere with iodine absorption. Examples include soy, sweet potato and cabbage family vegetables like broccoli, cauliflower and cabbage. If your intake of iodine is typically adequate, normal portions of these foods shouldn’t have any negative impact. The main concern would be if you were consuming inadequate iodine while also including lots of goitrogenic foods in your diet.

Who should be concerned about iodine intake? Vegans and vegetarians who avoid or limit dairy foods could be at risk for low iodine intake. Plant “milks” are not good iodine sources. Other than salt, foods are not fortified with iodine. One easy solution is to purchase iodized salt for home use. Another strategy is to include sea vegetables in moderate amounts. Vegetarians can include dairy foods (milk and yogurt are particularly good iodine sources).

Can iodine boost metabolism

Some websites and nutritionistas promote the idea that taking iodine boosts metabolism by boosting thyroid hormone production. This is false. If you have sufficient iodine, and your thyroid is functioning normally, additional iodine will not lead to more thyroid hormone in your system. The only time additional iodine would be helpful is if you had an outright deficiency.

Many people have low thyroid function. It’s more common as we age. In the absence of deficiency, iodine supplements will not help, as the problem is more about thyroid function than iodine supply.


Most multiple vitamins have iodine. Many contain the recommended daily intake for an adult (150 mcg), even some supplements aimed at children. So if you take a multiple, you are probably getting more than sufficient iodine.

You can get too much iodine. The Tolerable Upper Intake Level for an adult is 1100 mcg, almost 8 times the recommended intake. Strangely, excess iodine can cause some of the same problems as deficiency: goiter and hypothyroidism. In extreme cases, excess iodine can inflame the thyroid gland and lead to other severe symptoms. Furthermore iodine supplements can interact with many common medications.

Take Away

  • Your most predictable source of iodine is iodized salt.
  • Vegans and some vegetarians are at risk for poor iodine intake due to avoidance of dairy foods.
  • Don’t take iodine because you think it will boost your metabolism.
Copyright: All content © 2021 Nutrition Strategy Advisors LLC. Photographs © Donna P Feldman, unless otherwise attributed. Reproduction or use without permission is prohibited.