Plain language summary
Popularity to follow a vegan or vegetarian diet has increased in recent years, however iodine deficiency may be an issue in this cohort of people due to the body's low ability to utilise plant-based iodine compared to that of meat. The aim of this systematic review of 15 studies was to assess the iodine status of adults following a vegan or vegetarian diet. The results showed that vegans followed by vegetarians had the lowest iodine status across the studies and both were at suboptimal amounts. However, vegans had higher dietary intakes than vegetarians. Omnivores had the greatest intake of iodine. Seaweed was the main source of iodine for vegans. It was concluded that vegans and vegetarians not consuming seaweed or taking supplements are at an increased risk of iodine deficiency compared to adults on a less restrictive diet. Iodine status needs to be monitored and research into improving the iodine status of vegans and vegetarians is needed. This study could be used by healthcare professionals to understand that vegans and vegetarians may be at risk of iodine deficiency with a view to recommending seaweed to those who have low iodine intakes.
Abstract
Vegan and vegetarian diets are becoming increasingly popular. Dietary restrictions may increase the risk of iodine deficiency. This systematic review aims to assess iodine intake and status in adults following a vegan or vegetarian diet in industrialised countries. A systematic review and quality assessment were conducted in the period May 2019-April 2020 according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Studies were identified in Ovid MEDLINE, Embase, Web of Science, PubMed, Scopus, and secondary sources. Fifteen articles met inclusion criteria. Participants included 127,094 adults (aged ≥ 18 years). Vegan groups presented the lowest median urinary iodine concentrations, followed by vegetarians, and did not achieve optimal status. The highest iodine intakes were recorded in female vegans (1448.0 ± 3879.0 µg day-1) and the lowest in vegetarians (15.6 ± 21.0 µg day-1). Omnivores recorded the greatest intake in 83% of studies. Seaweed contributed largely to diets of vegans with excessive iodine intake. Vegans appear to have increased risk of low iodine status, deficiency and inadequate intake compared with adults following less restrictive diets. Adults following vegan and vegetarian diets living in countries with a high prevalence of deficiency may be more vulnerable. Therefore, further monitoring of iodine status in industrialised countries and research into improving the iodine intake and status of adults following vegan and vegetarian diets is required.
Methodological quality
Jadad score
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Allocation concealment
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