Written by Elizabeth Eveleigh
This year 125,000 people in the UK pledged to follow a vegan diet for one month for ‘Veganuary’ (Veganuary, 2021). People may choose to follow a vegan diet for environmental, ethical, religious, health or social reasons. Vegan diets are typically defined by the elimination of animal products and if well planned, are regarded to be suitable throughout the lifespan (BDA, 2017). Despite this, making drastic changes to our diet, in any way, will affect micronutrient intake. As ‘Veganuary’ comes to a close and we enter another month of lockdown, millions will be contemplating continuing their vegan diet. Many will be unaware of how their new food choice impacts iodine intake.
Iodine is an essential micronutrient, vital for the synthesis of the thyroid hormones—triiodothyronine (T3) and thyroxine (T4) (Eastman and Zimmermann, 2018), which regulate metabolism, growth, and neurological development (Eastman and Zimmermann, 2018). Too little or too much iodine can cause health problem. Iodine deficiency presents as a spectrum of conditions termed ‘iodine deficiency disorders’ (IDD’s) which occur when recommended intakes are not achieved (150 µg day−1). In mild-to-moderate iodine deficiency, undesirable symptoms can occur as the thyroid gland attempts to maintain normal function (hypothyroidism) (Zimmermann, 2009). Goitre, the enlargement of the thyroid gland, is the most obvious sign of severe deficiency and can occur at any age (Zimmermann, 2009). Excessive iodine intake (>1000 µg day−1) may lead to over production of the thyroid hormones (hyperthyroidism) (Leung and Braverman, 2014). The prevalence of IDDs differs globally. In the UK, iodine deficiency has re-emerged and is now recognised as a major public health concern in the UK (Woodside and Mullan, 2020).
Iodine is only provided by the diet, therefore our food choices control iodine intake. The iodine content of different foods vary. The main food sources of iodine in the UK are cow’s milk, dairy products, eggs, and white fish (Bath and Rayman, 2016). The problem? Vegans don’t eat these foods. For this reason, vegans are much more susceptible to inadequate intake and iodine deficiency (Eveleigh et al., 2020).
So, where are vegans getting their iodine from?
Most countries iodise table salt to prevent deficiency. Universal salt iodisation doesn’t currently exist in the UK and fortified salt is difficult to purchase in mainstream supermarkets (Bath, Button and Rayman, 2014). Iodised salt is not encouraged to improve iodine in the UK, because as a nation we need to cut back on salt to reduce hypertension.
Plant-sources are typically low in iodine and vary in content depending on the availability of iodine in the soil (Fuge, 2013). Conversely, kelp and other seaweeds contain high concentrations of iodine (Yeh, Hung and Lin, 2014), but are not recommended to improve iodine intake. This is because the iodine content of seaweed is so great that, unless iodine content is monitored, regular consumption could lead to excess (Leung and Braverman, 2014).
Plant-based milks are becoming the norm and are regularly used to replace cow’s milk. Although they are advertised as an appropriate substitute, these milks are not naturally iodine rich (Bath et al., 2017). Recent analysis of the NDNS discovered that consuming unfortified plant-milks could significantly heighten your risk of iodine deficiency (Dineva, Rayman and Bath, 2020). Those not consuming cow’s milk should select fortified alternative milk varieties that contain ‘potassium iodide’ or ‘potassium iodate’.
Vegan’s not consuming iodine fortified food may benefit from supplementation. Research investigating iodine supplements in mild-to-moderate deficient adults discovered that supplementing 150 ug day-1 of iodine for 24 weeks significantly improved iodine intake (Ma et al., 2016). Worryingly, it is estimated that the existing global reserves of iodine will only support production for a couple of centuries.
From my research, there appears to be an urgent need to identify a widely available and sustainable iodine source suitable for vegans. For now, be reassured that, whatever dietary choices you make, it is possible to meet your iodine requirements. If you are choosing to follow a vegan diet past ‘Veganuary’, you may need to pay extra attention to where you are getting your iodine from.
Un-supervised supplement usage could lead to adverse consequences. If you are unsure about how you can meet iodine intake recommendations, you can seek personalised advice from a registered dietitian or AfN-registered nutritionist who can support you to ensure that your diet is healthy, balanced, and iodine rich.
Bath, S. C. et al. (2017) ‘Iodine concentration of milk-alternative drinks available in the UK in comparison with cows’ milk’, British Journal of Nutrition, 118(7), pp. 525–532. doi: 10.1017/S0007114517002136.
Bath, S. C., Button, S. and Rayman, M. P. (2014) ‘Availability of iodised table salt in the UK - is it likely to influence population iodine intake?’, Public health nutrition, 17(2), pp. 450–4. doi: 10.1017/S1368980012005496.
Bath, S.C., and Rayman, M. (2016) ‘British Dietetic Association: Iodine Food Fact Sheet’.
Dineva, M., Rayman, M. P. and Bath, S. C. (2020) ‘Iodine status of consumers of milk-alternative drinks versus cows’ milk: Data from the UK National Diet and Nutrition Survey’, British Journal of Nutrition. doi: 10.1017/S0007114520003876.
Eastman, C. J. and Zimmermann, M. B. (2018) ‘The Iodine Deficiency Disorders’.
Eveleigh, E.R. et al. (2020) 'Vegans, Vegetarians, and Omnivores: How Does Dietary Choice Influence Iodine Intake? A Systematic Review', Nutrients. doi: /10.3390/12061606.
Fuge, R. (2013) ‘Soils and iodine deficiency’, in Essentials of Medical Geology: Revised Edition. Springer Netherlands, pp. 417–432. doi: 10.1007/978-94-007-4375-5_17.
Leung, A. M. and Braverman, L. E. (2014) ‘Consequences of excess iodine.’, Nature reviews. Endocrinology, 10(3), pp. 136–42. doi: 10.1038/nrendo.2013.251.
Ma, Z. F. et al. (2016) ‘Iodine Supplementation of Mildly Iodine-Deficient Adults Lowers Thyroglobulin: A Randomized Controlled Trial’, The Journal of Clinical Endocrinology & Metabolism, 101(4), pp. 1737–1744. doi: 10.1210/jc.2015-3591.
Woodside, J.V. and Mullan, K.R. (2020) 'Iodine status in UK–An accidental public health triumph gone sour', Clinical Endocrinology. doi: 10.1111/cen.14368.
Yeh, T. S., Hung, N. H. and Lin, T. C. (2014) ‘Analysis of iodine content in seaweed by GC-ECD and estimation of iodine intake’, Journal of Food and Drug Analysis, 22(2), pp. 189–196. doi: 10.1016/j.jfda.2014.01.014.
Zimmermann, M. B. (2009) ‘Iodine deficiency’, Endocrine Reviews, pp. 376–408. doi: 10.1210/er.2009-0011.
Elizabeth Eveleigh is a PhD researcher at The University of Nottingham investigating the influence of restrictive diets on iodine nutrition and thyroid health. Additional research interests include: vegan and vegetarian diets, alternative food products and improving population micronutrient status.