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The popularity of vegetarian and vegan diets is growing due to increased awareness of the environmental and health benefits of such diets. However, despite the consumption of meatless diets being associated with decreased risk of chronic diseases and mortality, followers of these diets are prone to certain nutritional inadequacies, which could limit health benefits. The main nutrients of concern are vitamin B12, vitamin D, iodine, selenium, calcium, and iron. It is essential for all those following vegetarian and vegan diets to implement vitamin B12 supplementation. To prevent vitamin B12 deficiency, adults should take one oral dose of 50–100 μg cyanocobalamin daily or 2000 μg weekly divided into two oral cyanocobalamin doses. Iodine supplementation is essential for pregnant and breastfeeding women and is recommended for vegetarians and vegans who are unable to access sea vegetables or iodine-fortified foods. The recommended dose of iodine supplement for adults is 150 μg daily. Selenium supplementation should be reserved for individuals with clinical evidence of deficiency due to concerns of adverse effects on lipid profiles and type 2 diabetes risk. It is recommended that vegetarian and vegan adults should supplement 4000 International Units (IU)/d of oral vitamin D to prevent deficiency as sunlight exposure is unreliable due to a range of lifestyle and environmental factors. This recommendation also applies to omnivores. As a precaution, those wishing to transition to a more plant-based diet should consider how they will substitute the nutrition they currently obtain from animal-based foods with plant-based sources or appropriate supplementation.
Gibbs et al. (Sat,) studied this question.