Iodine intake has been decreasing in the U.S. since the early 70s as a result of changes in Americans’ food and dietary habits, and because, as recently published research shows, iodized salt may contain far less than the amount of iodine listed on the label.
Milk, and therefore dairy products, used to be a decent source of this important trace mineral, but their iodine content has greatly decreased due to changes in cattle feed and a phase out of iodine dairy sanitizers. The average iodine content of U.S. whole cow’s milk has plummeted from 184 mcg/L) in 1978 to 19 mcg/L in 1989-90.
Sea vegetables, such as kelp, dulse, hijiki, and nori, remain an excellent source of iodine (a mere 1/4 cup supplies 415mcg), but are not frequent American fare, and unless certified organic, may contain heavy metals.
This leaves iodized salt as the major source of dietary iodine for the U.S. population. Unfortunately, relying on salt for our iodine may not be effective for a number of reasons.
Americans have been told to limit salt intake and are taking the advice to heart. Because excessive sodium intake can increase hypertension risks, many agencies now recommend reducing salt intake. A 1995 report found 58% of men and 68% of women reported never using salt, using “lite” salt, or rarely using ordinary table salt. More recently, the American Medical Association has suggested that the FDA remove salt from the “Generally Recognized as Safe” list. (Interagency Board for Nutrition Monitoring and Related Research. Third Report on Nutrition Monitoring in the United States. Executive Summary; 1995; Page ES-10; http://www.cdc.gov/nchs/data/misc/tronm.pdf.)
Even those of us not actively limiting our salt intake may not be getting much iodine along with our sodium.
A study published in the January 2008 issue of Environmental Science and Technology, Dasgupta P, Liu Y, et al. indicates iodized salt is not likely to contain the amount of iodine it’s supposed to, and even if it did, virtually all of the salt actually used in prepared foods in the U.S. is not iodized.
According to product labels, all U.S. iodized salt contains 45 mcg of iodine per gram, but when the University of Texas researchers analyzed 88 samples of iodized table salt from 40 states, 53% of samples contained less. Iodine values in freshly opened, top-of-the can samples averaged 44.1 mcg/kg, but actual values ranged from as little as 12.7 to 129 mcg/kg. And the amount of iodine within each can was not homogenous but varied as much as 3.3 times among the 5 samples taken at different depths from the same container. Iodine was also found to decrease greatly during high humidity storage, although light or heat had little effect. (Dasgupta P, Liu Y, Dyke J. Iodine nutrition: iodine content of iodized salt in the United States. Environ. Sci. Technol., 42 (4), 1315-1323, 2008.)
In sum, if you’re using iodized salt, you have no idea how much iodine it is actually providing, and the longer you’ve had that container of salt, the more likely it’s iodine content has decreased.
In addition, in the U.S., the use of iodized salt is not mandatory either in restaurants or food processing. Americans are eating out a lot and even when eating at home, often rely on prepared processed foods. So, although the prepared food we’re buying may be highly salted, with very few exceptions, the salt used by restaurants and fast-food outlets is non-iodized salt, and so is the salt used by food processors, who say they fear the possibility that iodized salt might change the flavor of their products.
This concern turns out to be unsupported by fact. In 2006, UNICEF invited delegates from the Republic of Moldova to Switzerland, where all salt for both human and animal consumption must be iodized, to convince them to use iodized salt in food production. Iodine deficiency is common in Moldova where, every year, approximately 27,000 newborn babies suffer from brain damage as a result—a tragedy that using iodized salt in processed foods can eliminate. Delegates visited food factories where they found that the addition of iodine to Swiss bread, baked goods, and world-renowned cheeses causes no change in the taste or consistency of these foods. (Summary here.)
Switzerland used to have high levels of iodine deficiency. In 1806, when Napoleon ordered the Prefect of the Swiss Canton of Valais to conduct a survey for military service recruitment, out of 70,000 inhabitants, 4,000 were diagnosed with cretinism. Later, researchers discovered that cretinism, along with goiter (swelling of the thyroid gland in the neck) and, more importantly, mental retardation, were direct effects of iodine deficiency.
Iodine is necessary for the body’s production of thyroid hormones, which, in addition to regulating metabolic rate, direct brain development, so iodine is critical in the fetus (the brain is formed during the 1st trimester of pregnancy), infants and children (brain development continues through adolescence). Lack of sufficient iodine is the leading cause of preventable mental retardation in the world. Even a mild iodine deficit in pregnant women, infants, and children, can lower intelligence by 10-15 IQ points, lessening an individual’s mental abilities throughout life.
Switzerland introduced iodized salt in 1922, and since 1960, has eliminated iodine deficiency through universal salt iodization–providing iodine through all salt for human (including table salt and salt used for industrial food production) and animal consumption. Both the visible signs, like cretinism and goiter, as well as the more important hidden effects of iodine deficiency on brain development and IQ, have completely disappeared in Switzerland.
A vastly different situation currently exists in the US. Public-health studies over the past 30 years indicate that iodine levels in the U.S. population, particularly in women of childbearing age, are too low. Urinary iodine (the standard means of evaluating iodine levels in the body) has plummeted by almost 50% in adults, and the frequency of moderate iodine deficiency (urinary iodine excretion of less the 50 mcg per liter) in pregnant women has jumped from 1% to 7%. To underscore how low this is, the WHO defines iodine deficiency as a urinary iodine excretion of anything less than 100 mcg per liter, and estimates that, world-wide, approximately 2 billion people, including 285 million school-age children, are iodine-deficient.
In a recent editorial in the New England Journal of Medicine entitled “Iodine Nutrition – More is Better,” thyroidologist Robert Utiger of Harvard Medical School urges that the recommended daily intake of iodine be increased to 300 to 400 mcg, a dosage he feels can best be met through a universal salt iodization program similar to Switzerland’s. (Utiger RD, N Engl J Med. 2006 Jun 29;354(26):2819-21, PMID: 16807421)
Utiger’s suggested RDA is significantly higher than current U.S. recommendations (see Table: Recommended values of iodine intake in the U.S.), but he argues that the most recent data shows the small easily correctable risks of possible excess iodine consumption are far outweighed by the substantial irremediable risks of iodine deficiency, which is widespread. (Teng W, Shan Z, Teng X, et al. Effect of iodine intake on thyroid diseases in China. N Engl J Med 2006;354:2783-93.)
“The best way to address this issue is to at least assure that iodized salt contains the amount of iodine it should, ideally to raise the iodine content of salt, and get the food processors to use iodized salt,” says Utiger.
What can you do now to ensure an adequate intake of iodine?
- Check your multiple vitamin and mineral supplement to be certain it provides at least 150 mcg per day. If you are pregnant, trying to become pregnant or breast-feeding, your pre-natal supplements should deliver at least 290 mcg per day.
- Use iodized salt when cooking at home and carry a small container in your purse or briefcase for use in restaurants.
- Experiment with sea vegetables. Many can be found in the form of flakes or powder as well as strips or sheets.
- Nori-used in sushi rolls is also available in seasoned snack-size strips, great for crumbling over soups or salads.
- Kelp-light brown to dark green strips, can often be found in flake form.
- Dulse-a reddish-brown seaweed that is soft and chewy in texture, can be found ground fine for use as a salt substitute.
- Kombu-add a strip to beans while cooking; it will help prevent gas and add flavor.
- Wakame-used to make Japanese miso soup.
- Arame-a lacy sea vegetable with a sweeter, milder taste, adds salty flavor to soups or stews.
- Hijiki-looks like strands of wiry, black pasta, a great addition, in small amounts (it’s quite flavorful), to carrot salad. Soak hijiki and mix with shredded carrots, chopped pickled ginger, sesame seeds and oil, a little finely sliced scallion, and a dash of tamari.
One important caveat: Purchase only certified organic sea vegetables to ensure they are free of contamination. Sea vegetables have a high affinity for heavy metals, and if grown in polluted waters, can soak up not only healthful minerals, but also contaminants such as arsenic, lead, cadmium or mercury.
(van Netten C, Hoption Cann SA, Morley DR, van Netten JP. Elemental and radioactive analysis of commercially available seaweed. Sci Total Environ. 2000 Jun 8;255(1-3):169-75. PMID: 10898404)