component of thyroid hormones but is also a microenvironment for thyroid cells to thrive. A U curve has been proved by a number of studies, indicating that both iodine deficiency and iodine excess can result in an increased prevalence of thyroid disorders. Over the past 25 years, universal salt iodization (USI) has been introduced in many countries as a safe, cost-effective and sustainable method to eliminate iodine deficiency disorders (IDDs), resulting in a greatly improved iodine status. However, an increased iodine intake has brought new challenges in long-term iodine sufficient regions covered by USI for more than 10 years. This review focused on the effect of iodine excess on thyroid disorders in China and other regions in the world.