The epidemiology of global micronutrient deficiencies.

Micronutrients are essential to sustain life and for optimal physiological function. Widespread global micronutrient deficiencies (MNDs) exist, with pregnant women and their children under 5 years at the highest risk. Iron, iodine, folate, vitamin A, and zinc deficiencies are the most widespread MNDs, and all these MNDs are common contributors to poor growth, intellectual impairments, perinatal complications, and increased risk of morbidity and mortality. Iron deficiency is the most common MND worldwide and leads to microcytic anemia, decreased capacity for work, as well as impaired immune and endocrine function. Iodine deficiency disorder is also widespread and results in goiter, mental retardation, or reduced cognitive function. Adequate zinc is necessary for optimal immune function, and deficiency is associated with an increased incidence of diarrhea and acute respiratory infections, major causes of death in those <5 years of age. Folic acid taken in early pregnancy can prevent neural tube defects. Folate is essential for DNA synthesis and repair, and deficiency results in macrocytic anemia. Vitamin A deficiency is the leading cause of blindness worldwide and also impairs immune function and cell differentiation. Single MNDs rarely occur alone; often, multiple MNDs coexist. The long-term consequences of MNDs are not only seen at the individual level but also have deleterious impacts on the economic development and human capital at the country level. Perhaps of greatest concern is the cycle of MNDs that persists over generations and the intergenerational consequences of MNDs that we are only beginning to understand. Prevention of MNDs is critical and traditionally has been accomplished through supplementation, fortification, and food-based approaches including diversification. It is widely accepted that intervention in the first 1,000 days is critical to break the cycle of malnutrition; however, a coordinated, sustainable commitment to scaling up nutrition at the global level is still needed. Understanding the epidemiology of MNDs is critical to understand what intervention strategies will work best under different conditions.