Iodine and Thyroid Health: Putting 2 and 2 Together
According to the American Thyroid Association, >12% of the US population will develop a thyroid condition during their life. Women are 5 times more likely than men to have thyroid problems. Although the causes of thyroid problems are largely unknown, iodine, a trace element found in soil, is an essential component of thyroid hormones – thyroxine (T4) and triiodothyronine (T3). Iodine deficiency disorders include hypothyroidism, goiter, cretinism, mental retardation, and developmental abnormalities.
Iodine deficiency is a geographical concern caused primarily when people eat food grown in regions with very little iodine in the soil. Why? Because our iodine intake is a reflection of the amount of iodine which can be extracted by plants from the soil. Xinjiang province of China is such a unique geographical location. Guo and colleagues report 1/3 of the population in Xinjiang are iodine deficient. Unless these people start to consume iodized salt or fortified foods, iodine deficiency will prevail.
Thyroid disorders, both hyper- and hypo-thyroidism and subclinical hypothyroidism were more prevalent in the iodine-deficient Xinjiang residents. Urinary iodine excretion is a simple approach to assess iodine intake. The median urinary iodine concentration (UIC) measured in Xinjiang residents was 130.7 µg/L. This is similar to the median 144 µg/L measured in US adults (NHANES 2009-2010).
One of the Dietary Guidelines 2015-2020 recommendations is to “Consume less than 2,300 milligrams (mg) per day of sodium.” This recommendation calls for us to reduce salt consumption.
Fortification of salt with iodine in the United States is voluntary and specialty salts (sea salt, kosher salt, etc) are rarely fortified. In fact, only 53% of retail food products for sale in the United States contain iodized salt.
NHANES biochemical data shows iodine intake in the US is decreasing. According to NHANES 2007-2008, median UIC was 164 µg/L whereas the median UIC was 144 µg/L in NHANES 2009-2010 . Are people reducing their salt intake? Maybe. Maybe not. Is iodine intake falling because people are opting for natural/organic food and beverage choices (and table/cooking salt options) that aren’t iodized?
Regardless of one’s position on salt consumption, iodine intake is falling. Iodine is essential for normal thyroid function. The US Preventive Services Task Force (USPSTF) concluded that the evidence is insufficient to screen for thyroid dysfunction in nonpregnant, asymptomatic adults. Maybe they should have recommended urinary iodine testing.
If you read this blog regularly, you know I strongly favor nutrition status monitoring using biochemical means. Iodine is another nutrient of concern. We should be monitoring nutrient concentrations, in this case iodine, so we can determine if our nutrient status is adequate. Good nutrition can maintain health and maintain quality of life, hopefully without having to buy drugs.
Guo Y, Zynat J, Xu Z, Wang X, Osiman R, Zhao H, Tuhuti A, Abdunaimu M, Wang H, Jin X, Xing S. Iodine nutrition status and thyroid disorders: a cross-sectional study from Xinjiang autonomous region of China. 2016 EJCN doi: 10.1038/ejcn.2016.82
Kapil U. Health consequences of iodine deficiency. 2007 Sultan Qaboos Univ Med J 7:267-272
Caldwell KL, Pan Y, Mortensen ME, Makhmudov A, Merrill L, Moye J. Iodine status in pregnant women in the National Children’s Study and US Women (15-44 years), National Health and Nutrition Examination Survey 2005-2010. 2013 Thyroid doi: 10.1089/thy.2013.0012
Maalouf J, Barron J, Gunn JP, Yuan K, Perrine CG, Cogswell ME. Iodized salt sales in the United States. 2015 Nutrients doi: 10.3390/nu7031691