Iron deficiency is believed to affect 20–50% of the world's population, making it the most common nutritional deficiency in the world. Iron deficiency, anemia or both are associated with a wide variety of adverse health outcomes, including delayed child development, lower IQ, poor school achievement, decreased active play in children, lethargy and fatigue, decreased physical work capacity, decreased work productivity in repetitive tasks, preterm birth, low birth weight, perinatal mortality, infant and young child mortality, and maternal mortality. Yet most national control programs have not been successful, and global prevalence has not declined.