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.
Highlights
Vegan and vegetarian diets have gained popularity over the past decade
Well-planned vegan and vegetarian diets have been regarded by the British Dietetic Association and other organizations in industrialised countries to be suitable throughout the lifespan, inclusive of infancy and pregnancy [3,4,5]
The technique of study selection along with the number of included and excluded studies recorded for this systematic review is shown in the PRISMA 2009 flow diagram (Figure 1) [32]
Summary
Vegan and vegetarian diets have gained popularity over the past decade. Characteristically, vegans do not consume any animal-derived products including eggs, dairy, meat, and fish. A subclass of the vegetarian diet may consume fish but not meat, termed pescatarians. Despite these definitions, varying levels of strictness and adherence to dietary restriction exist at the level of the individual [1]. Meat-free diets are traditionally adopted owing to religious, social, ecological, or economic constraints as opposed to personal choice [2]. Populations in developed countries may adopt these diets for environmental, ethical, religious, health beliefs or social reasons. Well-planned vegan and vegetarian diets have been regarded by the British Dietetic Association and other organizations in industrialised countries to be suitable throughout the lifespan, inclusive of infancy and pregnancy [3,4,5]. Concerns have been raised regarding the ability of these diets to adequately provide essential micronutrients, such as iodine [6]
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