Effects of poverty on cognitive function: a hidden neurologic epidemic.

Mental retardation is one of the most prevalent neurologic disorders globally. Surveys in high-income countries show 3 to 5 per 1,000 with severe intellectual disability, i.e., IQ below 55. Estimates from developing countries, however, have found prevalence rates from 5 to as much as 22 per 1,000. Protein-energy malnutrition, dietary micronutrient deficiencies, environmental toxins, and lack of early sensory stimulation or the ability to profit from it may contribute to neurodevelopmental disabilities. Tropical diseases such as parasitosis with resultant anemia, malaria, and other infections are major contributory causes. Reduction of poverty and its effects would reduce the present and future burden of mental retardation and cognitive dysfunction, especially in developing countries.