I is for …

Name the nutrient:

• A deficiency of this nutrient is the most common cause of preventable mental retardation.
• Over 30% of people worldwide don’t get enough of this nutrient.
• Even a mild deficiency of this nutrient in children can have lifelong effects on IQ and learning ability.
• Vegans may be at higher risk of not getting enough of this nutrient.

The mystery nutrient is not iron, or vitamin B12, or even protein.   Each of the points above describes iodine, an essential mineral.

We don’t need a lot of iodine; recommendations are expressed in micrograms (a microgram is one-millionth of a gram).  Without adequate iodine, however, babies’ brains don’t develop properly, children and adults can become hypothyroid, and pregnancies are more likely to end in miscarriage and stillbirth.  Iodine is used by the thyroid gland to make thyroid hormones and is essential for the thyroid gland to work properly.

Most of the iodine on the earth is found in the ocean.  The amount of iodine in soil varies considerably.  Areas close to the ocean have more iodine in the soil because of mist from the ocean.  Mountainous regions are often low in iodine because the erosion of the exposed soil leaches iodine.  Low-lying areas that are frequently flooded are also typically low in iodine.  Soil iodine content is important because it influences the amount of iodine in crops grown on that soil.  Fruits and vegetables grown on iodine-rich soil are higher in iodine than those grown in areas where the amount of iodine in soil is low.

Up until 1924, the year when iodine was added to salt in the United States, iodine deficiency was fairly common in the United States, especially in the Midwest and Great Lakes regions, the so-called Goiter Belt.  Goiter (an enlarged thyroid gland) can be due to iodine deficiency.   After iodized salt was introduced, the incidence of iodine deficiency dropped.

In the United States, both iodized and non-iodized salt are sold.  Only about 70% of the table salt sold in the United States is iodized, according to the Salt Institute.  Iodized salt is identified on the package label.  Food manufacturers, the fast-food industry, and restaurants frequently do not use iodized salt. As people eat out more often and buy more processed foods, iodine intakes in the United States have declined. The iodine content of food is rarely listed on food packages so, for most foods, consumers have no way of knowing the iodine content.

Foods that are high in iodine include iodized salt, dairy products (because of iodine in animal feed and iodine in the disinfectant that is sometimes used on milking machines), eggs, seafood, and some breads.  Most fruits, nuts, and vegetables are low in iodine, although their iodine content varies depending on the soil they’re grown on and irrigation and fertilization practices. Vegetarian and nonvegetarian diets that exclude iodized salt, fish, and sea vegetables have been found to contain very little iodine.  A recent study found that vegans in the Boston-area had lower iodine intakes than non-vegetarians.  Similar results have been reported for vegans in Sweden, Germany, and the United Kingdom.

Iodine recommendations vary depending on your age and other factors.  The Recommended Dietary Allowance (RDA) for teens and adults is 150 micrograms per day; for 1-8 year olds the RDA is 90 micrograms per day; and for 9-13 year olds it is 120 micrograms daily.  Pregnant women need 220 micrograms of iodine daily and women who are breastfeeding need 290 micrograms per day.

What can you do to make sure you’re getting the iodine you need?

Use iodized salt. Iodized salt can be used at the table and in cooking.  It is identified as iodized salt on the label.  Kosher salt does not contain iodine.  Natural sea salt contains little iodine.  Some brands of sea salt have iodine added – check the label.  For adults, a slightly rounded half teaspoonful of iodized salt provides the recommended amount of iodine.  If you’re pregnant or breastfeeding, you need more iodine –see below for recommendations especially for these times.

Use an iodine supplement. If you are watching your dietary sodium and don’t use much salt, or if you prefer to avoid iodized salt, a small daily iodine supplement is a good idea.  A regular multi-vitamin and mineral supplement may contain iodine – check the label. The amount of iodine in your supplement should be close to the RDA for your age group.  There are some concerns that supplements based on kelp vary widely in their actual iodine content.  If you’re relying on supplements as your main iodine source, it seems safer to not use kelp-based supplements.

If you’re pregnant or breastfeeding Since iodine is so important during pregnancy and infancy, the American Thyroid Association recommends that pregnant and breastfeeding women in the United States and Canada take a prenatal supplement that contains at least 150 micrograms of iodine daily.  Additional iodine for pregnant and breastfeeding women should come from iodized salt. Many prenatal supplements contain iodine but not all do; be sure to check the label.

Sea vegetables such as kombu, arame, and hijiki are rich sources of iodine although the amount of iodine in a serving of sea vegetables can be quite variable.  Some sea vegetables have been reported to contain very high amounts of iodine.  For example, a serving of kombu weighing about 5 grams may contain more than 7,000 micrograms of iodine, much more than is considered safe for daily use.  Long-term excessive iodine intake can be just as harmful as insufficient iodine, so don’t overdo sea vegetables, especially if you’re pregnant or breastfeeding.   The upper limit for iodine intake for adults is 1,100 micrograms per day.