According to the World Health Organization, which nutrient deficiency is among the most common worldwide?

Iron deficiency is recognized by the World Health Organization as one of the most prevalent nutrient deficiencies globally. This deficiency affects billions of people, particularly women and children, and can lead to significant health issues such as anemia. Iron is crucial for the production of hemoglobin, which carries oxygen in the blood, and its deficiency can result in fatigue, decreased immune function, and impaired cognitive development.

While calcium, vitamin D, and vitamin A deficiencies are also important public health concerns, none has the same widespread prevalence as iron deficiency. Calcium deficiency is often noted in specific populations but is not as globally widespread. Vitamin D deficiency has become more recognized, particularly in regions with limited sunlight exposure, but iron deficiency remains the most common. Vitamin A deficiency is critical in developing countries and poses serious health risks, especially in terms of vision and immunity, but its overall prevalence does not match that of iron deficiency. Thus, iron deficiency's extensive reach and impact on health solidify its status as the most common nutrient deficiency worldwide according to the World Health Organization.