The Problem Iodine Deficiency. Iodine is a micronutrient crucial for bone and brain development, including intelligence. However around 1.75 billion people--nearly a quarter of the world’s population--get too little iodine in their food. This leads to increased rates of miscarriage, stillbirth, and infant mortality, as well as cognitive and developmental problems, goiter, and hypothyroidism. Iodine deficiency is the leading preventable cause of intellectual and developmental disabilities in the world. Much progress has already been made. The number of iodine deficient countries was reduced from 55 in 2003 to just 19 in 2017. Yet despite many years of global Universal Salt Iodization (USI) efforts, about 25 percent of households in the developing world are still iodine deficient, many of them in areas that are the poorest and hardest to reach. New models are needed to ensure full and sustained coverage.