Iodine.
Iodine is essential for human growth, development and production of thyroid hormones. Although Australian soils are deficient in iodine and plant-based diets are typically low in sodium, sources of iodine can be obtained from nori (seaweed) and iodised salt. However, as “80% of vegans, 25% of vegetarians and 9% of conventional eaters are iodine deficient" (Dietician's Associaiton of Australia, 2016), it is important to either supplement with iodine in a multivitamin or regularly consume kelp, other seaweeds or iodised salt.