Vegans and vegetarians living in Nottingham (UK) continue to be at risk of iodine deficiency

Abstract

Iodine is essential for thyroid hormone synthesis. Individuals adhering to vegan and vegetarian diets have been found to be vulnerable to iodine deficiency. Yet, iodine has not been monitored in these groups across time. This study aims to investigate iodine status, intake and knowledge in vegans, vegetarians, and omnivores and determine changes between 2016-17 and 2019. Dietary intake (µg day−1) was estimated by three-day food diaries (FD), and iodine food frequency questionnaires (FFQ). Urinary iodine concentration (UIC), analysed by ICP-MS, assessed iodine status according to World Health Organisation (WHO) criteria. Iodine knowledge was scored by an adapted questionnaire. IBM SPSS was used for statistical analysis. Ninety-six adults (18-60 y) were recruited in October 2016-17 (vegans; 12, vegetarians; 5, omnivores; 43) and June 2019 (vegans; 7, vegetarians; 10, omnivores; 19). Median dietary iodine was below the Reference Nutrient Intake (RNI) for all groups. Vegans and vegetarians had the lowest iodine intake. Vegans had significantly lower iodine intake than omnivores (2016-17; P = 0.032, 2019; P = 0.001). Omnivores had the highest iodine status (2016-17; 79.4 µg L−1, 2019; 72.4 µg L−1), and vegans the lowest (2016-17; 31.2 µg L−1, 2019; 12.2 µg L−1). Iodine knowledge was poor, but did not differ between dietary groups (2016-17; P = 0.219, 2019; P = 0.532). Vegans and vegetarians continue to be at risk of iodine deficiency. Further, iodine intake in the UK is poor independent of dietary choice. Iodine education is needed along with, research into improving iodine nutrition at national level.

Systematic review and meta-analysis of iodine nutrition in modern vegan and vegetarian diets

“…Vegan participants had the lowest median UIC in all 5 studies (12.2 -44.0 µg L −1 ) (34,51,53,56,57) , with the lowest value recorded by Eveleigh et al in UK vegans (12.2 µg L −1 ) (34) . In all studies, vegans had significantly lower median UIC compared to omnivores (P < 0.05) (34,51,53,56,57) .…”

“…Vegan participants had the lowest median UIC in all 5 studies (12.2 -44.0 µg L −1 ) (34,51,53,56,57) , with the lowest value recorded by Eveleigh et al in UK vegans (12.2 µg L −1 ) (34) . In all studies, vegans had significantly lower median UIC compared to omnivores (P < 0.05) (34,51,53,56,57) . Vegetarians in the included studies tended to have median UIC values greater than vegans but lower than omnivores, flexitarians, and pescatarians (51,53) .…”

“…Iodine status by UIC was investigated in 5 studies with a total of 700 participants (vegan; 271, vegetarian; 135, pescatarian; 35, omnivore; 189, flexitarian; 70) (34,51,53,56,57) (Figure 2). Three studies assessed UIC using single spot urine samples (34,53,57) ; the remaining 2 studies used 24h urinary samples (51,56) . We were unable to separate UIC estimates by gender, as all included studies provided either mixed gender estimates or estimates in females alone.…”

“…None of the dietary groups included in this review had median UIC values within the optimal range for iodine status (100-200 µg L −1 ) according to WHO criteria and would be classified as iodine deficient (mild-severe; 50-99 µg L −1 ->20 µg L −1 ) (34,51,53,56,57) . Severe iodine deficiency (>20 µg L −1 ) was observed in one study of vegans living in the UK (34) .…”

“…Alternative dairy products such as alternative "milks" and "yogurts" are now regularly fortified with vitamin B12, D, and calcium (36)(37)(38)(39)(40) , but rarely with iodine (36,37,39) . Additionally, iodine supplements are still not universally consumed by individuals following vegan and vegetarian diets (34) .…”