The environment and mental retardation

A wide range of environmental factors affect intelligence and mental retardation. Biological risk factors for mental retardation include malnutrition; exposure to toxins such as lead, alcohol, and PCBs, and being born at LBW. Social influences from homes, schools, and cultures are related to intelligence and mental retardation although the direction of effect is difficult to determine. Randomized early intervention studies with children in poverty provide the best data showing that increased intelligence and adaptive behavior is possible, although significant and sustained effects only result from intensive services of long-term duration.