Vegans continue to be at risk of iodine deficiency across time

Researcher Network member, Elizabeth Eveleigh, investigates iodine deficiency in vegans.

Iodine is an essential micronutrient required to produce the thyroid hormones thyroxine (T4) and triiodothyronine (T3).¹ The thyroid hormones support neuronal development, metabolic function and growth.¹ In the UK, a Reference Nutrient Intake (RNI) of 140 μg of iodine is recommended to prevent deficiency and the development of iodine deficiency disorders such as goitre.^1,2 The main sources of dietary iodine in the UK are cows’ milk and dairy products.³ Seafood, eggs, seaweed and iodine-containing supplements are also rich in iodine.³ There is currently no national salt iodisation programme in the UK, a common public health method used in other countries to improve iodine intakes.^4,5

Iodine deficiency was prevalent in the UK in historical times, with populations in Derbyshire and Nottinghamshire exhibiting endemic goitre in the 18th and 19th centuries.⁶ Eradication began in the 1960s following government campaigns encouraging milk consumption and changes in farming practices.⁷ There has been a re-emergence of iodine deficiency in the UK in recent years related to a lower consumption of cows’ milk.⁷ A lower iodine intake has been observed in people who consume diets that exclude iodine-rich foods, principally dairy and/or fish, and those who do not consume fortified alternative milks.^8,9 For this reason, vegans are now recognised as a subgroup with increased risk of iodine deficiency.¹⁰

Although recognised as a micronutrient of concern, iodine has yet to be monitored across time in people following vegan diets. In addition, there is a lack of data regarding the level of knowledge about iodine in the general public and whether a good understanding of the challenges allows individual people to consider iodine when selecting foods to eat. In our most recent study, we investigated the intake and status of iodine and a knowledge of the importance of this micronutrient in those following vegan, vegetarian or omnivorous diets in Nottingham, a city with a historic link to iodine deficiency, across two years: 2016–17 and 2019.¹¹

Our study included 96 adults (aged 18 years and over) and confirmed that people adhering to vegan diets continue to be at risk of iodine deficiency in the UK. We found that people following vegan diets appear to have significantly lowered iodine status and inadequate iodine intake compared with adults following other diets (vegetarian and omnivorous). Our study highlights the ongoing public health issue of iodine deficiency in the UK and the urgent need to improve iodine intake. None of the dietary groups studied achieved the RNI for iodine or had an adequate iodine status regardless of dietary choice. We also found knowledge about iodine to be very low for all participants.

In both years, we found that those with the lowest dietary intake of iodine tended to identify as vegan. The average dietary intake for vegans was <70 µg per day, corresponding with current studies. This is of concern because a dietary intake <50 μg per day can potentiate the development of iodine deficiency disorders. The omnivores and vegetarians in our study also had low iodine intakes. The exclusion or substitution of iodine-rich animal products appears to act as a barrier to achieving the recommendations for iodine. At a policy level, mandatory fortification of alternative products mimicking cows’ milk may be beneficial given the popularity of these foods and the potential for them to improve iodine intake. Manufacturers should be encouraged to fortify their alternative drinks with iodine and the benefits of consuming iodine-fortified alternative milks must be better communicated to consumers.

We found a time-related decrease in iodine status in vegan and vegetarian participants from 2016–17 to 2019, aligning with a reduction in iodine status nationally. According to the WHO criteria for assessing population iodine status via the urinary iodine concentration,12 omnivorous participants presented values signifying mild deficiency and both vegans and vegetarians had values within the criteria for moderate deficiency in 2016–17 and severe deficiency in 2019.

Sufficient knowledge about iodine has been shown to be positively related to iodine intake and status.¹³ We found no difference in knowledge about iodine between the dietary groups, suggesting that dietary choice is not a predictor of iodine knowledge. Most participants in our study were not able to identify a health condition related to iodine deficiency and could not identify foods that are iodine-rich. Many participants selected leafy green vegetables and oily fish as good sources of iodine. Our results suggest that public health strategies are needed to improve public awareness of iodine.

Vegans and vegetarians are a subgroup at increased risk of iodine deficiency. People choosing vegan or vegetarian diets should be encouraged to select iodine-containing supplements or to consume fortified foods. Mandatory fortification of alternative milks may boost iodine intake for those not consuming cows’ milk. Formal education focusing on providing accurate and reliable information to vulnerable groups (vegans, vegetarians and young women) should be considered at a national level. It is vital to make efforts to increase awareness of the importance of iodine in the diet and to effectively communicate how iodine recommendations can be achieved by everyone, regardless of dietary choice. Further research aiming to improve the iodine status of those following vegan diets is required.

References

1. Zimmermann MB & Boelaert K. Iodine deficiency and thyroid disorders. The Lancet Diabetes & Endocrinology 2015; 3: 286–295, doi: 10.1016/S2213-8587(14)70225-6
2. Public Health England (PHE). Government Dietary Recommendations. Government Recommendations for Energy and Nutrients for Males and Females Aged 1–18 Years and 19+ Years. PHE Publications Gateway Number 2016202. London: PHE, 2016
3. Bath S & Rayman M. Iodine Food Fact Sheet. Birmingham: British Dietetic Association, 2016
4. Wu T, Liu GJ, Li P & Clar C. Iodised salt for preventing iodine deficiency disorders. Cochrane Database of Systematic Reviews 2002; 3: CD003204, doi:10.1002/14651858.cd003204
5. Bath SC, Button S & Rayman MP. Availability of iodised table salt in the UK – is it likely to influence population iodine intake? Public Health Nutrition 2014; 17: 450–454, doi:10.1017/S1368980012005496
6. Butler P-W & Turton PHJ. The distribution of simple goitre in Derbyshire. Proceedings of the Royal Society of Medicine 1933; 26: 1223–1266
7. Editorial: Iodine deficiency in the UK: Grabbing the low-hanging fruit. The Lancet Diabetes and Endocrinology 2016; 4: P469
8. Dineva M, Rayman MP & Bath SC. Iodine status of consumers of milk-alternative drinks versus cows’ milk: Data from the UK National Diet and Nutrition Survey. British Journal of Nutrition 2020; 126: 28–36, doi:10.1017/S0007114520003876
9. Eveleigh ER, Coneyworth LJ, Avery A & Welham SJM. Vegans, vegetarians, and omnivores: How does dietary choice influence iodine intake? A systematic review. Nutrients 2020; 12: 1606
10. Scientific Advisory Committee on Nutrition (SACN). SACN Statement on Iodine and Health – 2014. The Scientific Advisory Committee on Nutrition Review of Current Evidence on Iodine and Health. London: Public Health England, 2014
11. Eveleigh E, Coneyworth L, Zhou M, Burdett H, Malla J, Van Nguyen H & Welham S. Vegans and vegetarians living in Nottingham (UK) continue to be at risk of iodine deficiency. British Journal of Nutrition 2022; 21 Jan: 1–46, online ahead of print, doi:10.1017/S0007114522000113
12. World Health Organization (WHO). Vitamin and Mineral Nutrition Information System. Urinary Iodine Concentrations for Determining Iodine Status in Populations. WHO/NMH/NHD/EPG/13.1. Geneva: WHO, 2013
13. O’Kane SM, Pourshahidi LK, Farren, KM, Mulhern MS, Strain JJ & Yeates AJ. Iodine knowledge is positively associated with dietary iodine intake among women of childbearing age in the UK and Ireland. British Journal of Nutrition 2016; 116: 1728–1735, doi:10.1017/S0007114516003925

The views expressed by our Research News contributors are not necessarily the views of The Vegan Society.