A lovely systematic review has just been published by researchers from the University of Nottingham including a useful overview of all the studies that have tested the iodine status of vegans.
As animals who live in the sea and dairy products - because of fortified feed and contamination with iodine-containing disinfectants - are often rich sources of iodine, and as vegans we don't consume these things, vegan diets can be low in iodine ...
The easiest way to avoid a low iodine intake is with iodized salt, a supplement, or eating seaweed (like nori) in moderate amounts. Choose one, not all of these three options. See here for more precise recommendations.
39. Krajcovicová‐Kudlácková, M.; Bucková, K.; Klimes, I.; Seboková, E. Iodine deficiency in vegetarians and vegans. Ann. Nutr. Metab. 2003, 47, 183–5.
40. Leung, A.M.; LaMar, A.; He, X.; Braverman, L.E.; Pearce, E.N. Iodine status and thyroid function of Bostonarea vegetarians and vegans. J. Clin. Endocrinol. 2011, 96, 1303–7.
41. Lightowler, H.J.; Davies, G.J. Iodine intake and iodine deficiency in vegans as assessed by the duplicateportion technique and urinary iodine excretion. Br. J. Nutr. 1998, 80, 529–35.
44. Schüpbach, R.; Wegmüller, R.; Berguerand, C.; Bui, M.; Herter‐Aeberli, I. Micronutrient status and intake
in omnivores, vegetarians and vegans in Switzerland. Eur. J. Clin. Nutr. 2017, 56, 283–293.
48. Elorinne, A.‐L.; Alfthan, G.; Erlund, I.; Kivimäki, H.; Paju, A.; Salminen, I.; Turpeinen, U.; Voutilainen, S.; Laakso, J. Food and Nutrient Intake and Nutritional Status of Finnish Vegans and Non‐Vegetarians. PLoS ONE 2016, 11, e0148235.
50. Rauma, A.L.; Törmälä, M.L.; Nenonen, M.; Hänninen, O. Iodine status in vegans consuming a living food diet. Nutr. Res. 1994, 14, 1789–1795.
The easiest way to avoid a low iodine intake is with iodized salt, a supplement, or eating seaweed (like nori) in moderate amounts. Choose one, not all of these three options. See here for more precise recommendations.
Here's the table I find most interesting in this review article (nothing new or surprising). These are all the studies with vegans that tested iodine concentration in urine - which is a typical way to test iodine status.
As you can see, I have modified this table, adding the countries and the iodine status highlights (in red).
As the you can see from the table most studies with vegans show that on average mild or moderate iodine deficiency is common, but severe iodine deficiency or iodine excess from eating large amounts of seaweed can also occur.
Note: Iodine is very very important for pregnant women, breastfeeding women, and babies.
Here are the references for the table:
38. Henjum, S.; Brantsæter, A.L.; Kurniasari, A.; Dahl, L.; Aadland, E.K.; Gjengedal, E.L.F.; Birkeland, S.; Aakre, I. Suboptimal iodine status and low iodine knowledge in young Norwegian women. Nutrients 2018, 10. 941.39. Krajcovicová‐Kudlácková, M.; Bucková, K.; Klimes, I.; Seboková, E. Iodine deficiency in vegetarians and vegans. Ann. Nutr. Metab. 2003, 47, 183–5.
40. Leung, A.M.; LaMar, A.; He, X.; Braverman, L.E.; Pearce, E.N. Iodine status and thyroid function of Bostonarea vegetarians and vegans. J. Clin. Endocrinol. 2011, 96, 1303–7.
41. Lightowler, H.J.; Davies, G.J. Iodine intake and iodine deficiency in vegans as assessed by the duplicateportion technique and urinary iodine excretion. Br. J. Nutr. 1998, 80, 529–35.
44. Schüpbach, R.; Wegmüller, R.; Berguerand, C.; Bui, M.; Herter‐Aeberli, I. Micronutrient status and intake
in omnivores, vegetarians and vegans in Switzerland. Eur. J. Clin. Nutr. 2017, 56, 283–293.
48. Elorinne, A.‐L.; Alfthan, G.; Erlund, I.; Kivimäki, H.; Paju, A.; Salminen, I.; Turpeinen, U.; Voutilainen, S.; Laakso, J. Food and Nutrient Intake and Nutritional Status of Finnish Vegans and Non‐Vegetarians. PLoS ONE 2016, 11, e0148235.
50. Rauma, A.L.; Törmälä, M.L.; Nenonen, M.; Hänninen, O. Iodine status in vegans consuming a living food diet. Nutr. Res. 1994, 14, 1789–1795.
Reference for the systematic review including all these studies:
Eveleigh,
Elizabeth R.; Coneyworth, Lisa J.; Avery, Amanda; Welham, Simon J. M. (2020):
Vegans, Vegetarians, and Omnivores: How Does Dietary Choice Influence Iodine
Intake? A Systematic Review. In: Nutrients 12 (6). DOI:
10.3390/nu12061606.