Iodine is one of the main building blocks of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). Imbalanced thyroid hormone levels can lead to a great number of symptoms, like weight gain/loss, anxiety, depression, dry skin, hair loss, feeling cold/hot, and more. Since our bodies can’t produce iodine itself, we need to get enough of it in our diet. The iodine is absorbed from the food in our bowel, into our bloodstream. It is then carried to the thyroid gland, where it is eventually used to make thyroid hormones.
Although fish, shellfish, and seaweeds are the richest source of iodine on the planet, the most efficient source of iodine intake is still the use of salt (NaCl) which has been fortified with KI or KIO3 (iodized salt). The reason for this is, that the concentration of iodine in food and water is highly variable. This makes it difficult to determine how much iodine we consume from these natural sources. We need about 150 micrograms of iodine per day. And, yes, even living in a coastal seaweed-rich area supports adequate iodine intake; sea air is good for you!
How to prevent iodine deficiency?
Mild to moderate iodine deficiency is fairly common, and depending on the definition, can affect up to 50% of the European population. Yet, it is easily preventable through consumption of iodized salt (half a teaspoon per day), other iodine enriched foods like bread, or seaweed sprinkles (anyone?). If your iodine intake is low, a combination with very high intake of Brassica vegetables (cabbage, broccoli, cauliflower) increases the risk for iodine deficiency. These vegetables specifically contain goitrogens, substances that interfere with the uptake of iodine in the thyroid, which can exacerbate iodine deficiency. However, instead of avoiding these healthy vegetable, it is better to ensure sufficient iodine intake.
Iodine and pregnancy
A growing fetus in the womb of an iodine deficient mother is at high risk. The pregnancy may end in miscarriage, still birth, various birth defects or low birth weight. This makes iodine particular important for pregnant women, but also for children whose brain development depends on adequate levels of thyroid hormones. Pregnant women should therefore consume 200-220 microgram of iodine per day. This is also recommended during the breastfeeding period (assuming no deficiency at the start of/during the pregnancy).
de Benoist, B., Andersson, M., Takkouche, B. & Egli, I. Prevalence of iodine deficiency worldwide. Lancet (London, England) 362, 1859–60 (2003)
European Food Safety Authority. Scientific Opinion on Dietary Reference Values for iodine. (2014). Available at: https://efsa.onlinelibrary.wiley.com/doi/epdf/10.2903/j.efsa.2014.3660
Gärtner, R. Recent data on iodine intake in Germany and Europe. J. Trace Elem. Med. Biol. 37, 85–89 (2016)
Institute for Quality and Efficiency in Health Care. How does the thyroid gland work? (2010).
Leung, A. M., LaMar, A., He, X., Braverman, L. E. & Pearce, E. N. Iodine status and thyroid function of Boston-area vegetarians and vegans. J. Clin. Endocrinol. Metab. (2011). doi:10.1210/jc.2011-0256
National Institutes of Health. Iodine – Health Professional Fact Sheet. (2018). Available at: https://ods.od.nih.gov/factsheets/Iodine-HealthProfessional/
Pearce, E. N. Iodine deficiency disorders and their elimination. (Springer, 2017)
Smyth, P. P. A. et al. Does iodine gas released from seaweed contribute to dietary iodine intake? Environ. Geochem. Health 33, 389–397 (2011)
Zimmermann, M. B. Iodine Deficiency. Endocr. Rev. 30, 376–408 (2009)