Mineral Spotlight: Iodine

Iodine & Metabolism

Iodine is a trace mineral that plays a key role in metabolism, as it is fundamental to the formation of thyroid hormones.  The two main thyroid hormones, tetraiodothyronin (“T4”) and triiodothryonin (“T3”), are made up of iodine (4 atoms & 3 atoms, respectively) and tyrosine (Tortora & Derrickson, 2014).  Thyroid hormones increase basal metabolic rate, and regulate the body’s metabolism of carbohydrates, lipids, and proteins (Nix, 2017). 

Life Cycle Factors that Increase Iodine Needs

Iodine needs increase during pregnancy, as initially the fetus relies on the mother’s intake of iodine to meet its needs.  Because the mother’s iodine needs take precedence over the fetus, insufficient intake by the mother may have irreversible, negative impacts on the growing fetus, particularly in the area of neurodevelopment (Nix, 2017).  As a result, the RDA for pregnant and lactating women is increased to reflect this growing need (220mcg/day and 290mcg/day, respectively)(National Institutes of Health, 2011).

Iodine also plays an important role in growth and cognition during childhood and adolescence.  Iodine deficiencies during these life stages may cause stunted bone growth and impaired cognitive development (Tortora & Derrickson, 2014).  Iodine deficiencies have been associated with a decrease in IQ (Nix, 2017).  By contrast, correction of mild to moderate iodine deficiencies in the children may improve cognitive and motor function (Zimmermann, 2011).  

Appropriate Level of Supplementation 

A determination of the appropriate level of supplementation will take into account the above life cycle factors, and additional factors such as geographical location and the access to iodine rich vegetables, the use of iodized salt, and the intake of goitrogenic foods.  Because of the crucially important role iodine plays in the body, the RDA for iodine has been set at about 3 times the predicted minimal requirement (Nix, 2017).  The current RDA is 150 mcg/day for individuals 14 years and older, with an upper limit of 1,100 mcg/day, as excess iodine can have toxic effects (Nix, 2017).  

Food sources of iodine include seafood, sea vegetables, vegetables grown in iodine rich soils, and iodized table salt (which contains 77mcg of iodine per gram)(Nix, 2017).  However, one of the biggest problems with calculating the amount of iodine in foods is that the content is highly variable.  This is especially true of vegetables, as soil content of iodine varies greatly.  According to data provided by the World Health Organization (“WHO”), approximately 30% of the world’s population is deficient in iodine—especially in areas where soil iodine levels are poor (Nix, 2017).  Even the content of iodine in sea vegetables may vary greatly (National Institutes of Health, 2011). 

Table salt fortification with iodine, which began in the United States in the 1920s, is a common practice worldwide.  However, with the popularity of sea salt in recent years, some individuals may be getting less iodine in their diet. WHO data indicates that iodine deficiencies are higher in regions where individuals use less iodized salt (National Institutes of Health, 2011).  

Further, goitrogenic foods (especially when consumed raw) may interfere with iodine uptake by the thyroid gland (National Institutes of Health, 2011).  These include many healthy foods, such as the brassica family of vegetables. The level of consumption of these foods is another factor to take into consideration when determining an individual’s overall iodine needs.  

As a result, an appropriate level of supplementation will be personalised to take into account all of these important life cycle and lifestyle factors. 

References:

Nix, S. (2017). Williams' basic nutrition & diet therapy (15th ed.). Chapter 6. St. Louis, MO: Elsevier. 

Tortora, G.J., & Derrickson, B. (2014). Principles of anatomy & physiology (14th ed.). Chapter 18. Hoboken, NJ: John Wiley & Sons, Inc. 

National Institutes of Health. (2011, June 24). Iodine. Retrieved from https://ods.od.nih.gov/factsheets/Iodine-HealthProfessional/#h6

Zimmermann, M. B. (2011). The role of iodine in human growth and development. Seminars in cell & developmental biology 22(6), 645-652.