Iodine is an important trace element that is required by the thyroid to synthesise two hormones: triiodothyronine (T3) and thyroxine (T4). These hormones are crucial to the metabolism of almost all cells and tissues in the body [1].
Deficiency in iodine can lead to hypothyroidism, which means the body is unable to process enough thyroid hormones. Swelling in the neck due to an enlarged thyroid (goitre) will also present. This is a sign that the thyroid is not functioning properly. Hypothyroidism can lead to fatigue, constipation, muscle weakness, pain and swelling of joints, depression, and many other symptoms. For infants and children, severe cases of iodine deficiency can cause brain damage and mental retardation [2].
The common dietary sources of iodine are seafood, dairy products, egg, and iodised salts. The iodine content plant-based food such as vegetables is dependent on the environment and soil in which they are grown [3]. Nutritionally, vegetarian diets typically supply less iodine than non-vegetarian diets [4]. For this reason, vegetarians and vegans may have an increased risk of developing iodine deficiency, especially if their dietary is highly restrictive [5].
Here are some vegan food sources for iodine:
Seaweed
Seaweeds or sea vegetables are algae that grow in the sea with colour ranging from red, brown, to green. There are many different types of edible seaweed. Nori, wakame, and kombu are some of the Japanese seaweeds that are available worldwide. With the unique ability to concentrate iodine from the ocean, seaweeds are great sources for iodine. Dried nori contains 2200 μg in every 100g [6]. Not surprisingly, the Japanese people who consume more than 20 types of edible seaweed regularly are estimated to achieve an intake of 1,000-3,000 μg/day (1-3 mg/day) of iodine on average [7]. This amount is more than enough to meet the estimated recommended daily intake of 150 μg/day for adults [8].
Iodised salt
Iodised salt is normal table salt added with iodine. It was introduced in the early part of last century in industrialised nations to fight the wide-spread development to goitre in the population due to iodine deficiency. The use of iodized salt has been considered a successful public health scheme to help eliminate iodine-deficiency disorders in many parts of the world [9]. Some countries have made iodization of salt mandatory, that is, all table salt sold must be added with iodine. However, in some countries, like Singapore, the addition of iodine in salt is only voluntary [10]. Therefore, you must make sure that the salt you buy from the supermarket does contain iodine.
Miso paste
With the growing public awareness on the link between salt consumption and hypertension, more people no longer add salt to their food. This has also indirectly cut down their iodine intake, making iodine deficiency re-emerged. Although sensible use of iodized salt in cooking is necessary for health and will not lead to hypertension, some may want to flavour their cooking with alternative options. Miso paste which is made from fermented soybean is one good choice. 100g of miso paste contains about 120 μg of iodine. This is the same as what is found in an equal weight of raw egg or milk powder [6].
Prune
Prunes are dried plums. Nutritionally, prune is a rich source of dietary fibre and vitamin K. It is best known to be a remedy for constipation [11]. In addition, prunes are also rich in iodine. 100g of prunes contain close to 142 μg of iodine which is as high as fish such as Cod or Mackerel [6]. Prunes can be eaten as a snack, added to breakfast cereals, or juiced. Its use can be quite versatile.
Bread
Commercially baked bread is another good source of iodine today since salt is a required ingredient of bread. In places like Australia where bread is one of the staple food, the use of iodised salt in commercial bread making is a mandatory requirement since 2009 [12]. The content of iodine in bread ranges from 30+ to 137 μg per 100g [6].
Conclusion
Vegans are potentially more susceptible to low iodine content in the diet. While iodised salt is an easy remedy, using less salt is now recommended as a preventive measure for hypertension. To prevent iodine deficiency, vegans should consider including seaweed, miso, prune, and bread in the diet. Seaweed, in particular, has a high concentration of iodine and should be a key part of any vegan diet.
References
[1] H. Osiecki, The Nutrient Bible, 9th Ed., BioConcepts Publishing, Eagle Farm, OLD, Australia, 2014.
[2] W.M. Wiersinga, Adult Hypothyroidism, MDText.com, Inc., 2000. http://www.ncbi.nlm.nih.gov/pubmed/25905416 (accessed February 27, 2019).
[3] Iodine Facts | Nutrition Australia, (n.d.). http://www.nutritionaustralia.org/national/resource/iodine-facts (accessed February 27, 2019).
[4] T. Remer, A. Neubert, F. Manz, Increased risk of iodine deficiency with vegetarian nutrition, Br. J. Nutr. 81 (1999) 45–49. doi:DOI: 10.1017/S0007114599000136.
[5] C. Fields, J. Borak, Iodine Deficiency in Vegetarian and Vegan Diets , Evidence-Based Rev. World’s Lit. Iodine Content Veg. Diets . (2009) 521–531 BT–Comprehensive Handbook of Iodine. doi:10.1016/B978-0-12-374135-6.00054-6.
[6] A.N.Z.F. Authority, AUSNUT 2011-13 food nutrient database, Canberra, ACT, 2013. http://www.foodstandards.gov.au/science/monitoringnutrients/ausnut/ausnutdatafiles/pages/foodnutrient.aspx.
[7] T.T. Zava, D.T. Zava, Assessment of Japanese iodine intake based on seaweed consumption in Japan: A literature-based analysis, Thyroid Res. 4 (2011) 14. doi:10.1186/1756-6614-4-14.
[8] Iodine | Nutrient Reference Values, (n.d.). https://www.nrv.gov.au/nutrients/iodine (accessed February 27, 2019).
[9] U. Kapil, Successful efforts toward elimination iodine deficiency disorders in India, Indian J. Community Med. 35 (2010) 455–468. doi:10.4103/0970-0218.74339.
[10] K. Codling, C. Rudert, F. Bégin, J.P. Peña-Rosas, The legislative framework for salt iodization in Asia and the Pacific and its impact on programme implementation, Public Health Nutr. 20 (2017) 3008–3018. doi:10.1017/S1368980017001689.
[11] E. Lever, J. Cole, S.M. Scott, P.W. Emery, K. Whelan, Systematic review: the effect of prunes on gastrointestinal function, Aliment. Pharmacol. Ther. 40 (2014) 750–758. doi:10.1111/apt.12913.
[12] Iodine fortification, (n.d.). http://www.foodstandards.gov.au/consumer/nutrition/iodinefort/Pages/default.aspx (accessed February 27, 2019).