Mislead intelligence

Exposure to lead little has a weak but significant effect on the intelligence of children

Published: Wednesday 15 February 1995

A gasp of lead: the youngest c (Credit: T C Malhotra)DOES environmental exposure to lead affect the intelligence of children? Yes, according to a fresh interpretation of over 20 studies on the issue, which rules that at age 5 or more, a doubling of body lead is associated with a loss of 1-2 IQ (intelligence quotient) points. But children below 5 are not affected (British Medical Journal, Vol 309, No 6963).

Lead -- a poisonous metallic element known to cause several ailments ranging from stomach pain to blindness -- is present in the environment owing to contamination from lead paints and lead pipes or it is emitted into the atmosphere by motor vehicles and industries.

Stuart Pocock of the London School of Hygiene and Tropical Medicine and Marjorie Smith of London's Institute of Education -- in collaboration with Peter Baghurst at Commonwealth Scientific Industrial Research Organisation, Australia -- identified 26 most significant studies and used a systematic statistical method so as to quantify the overall magnitude of the relation between body lead and IQ in children aged 5 years or more. They also considered 5 prospective studies -- which measured the blood lead in children from before birth to the age of 5 -- in order to know whether neurotoxic effects occur in the foetus or shortly after birth.

The results suggest a loss of 1-2 IQ points in children above 5 when the body lead level is doubled, say from 10 microgram -- one in million parts of a gram -- to 20 microgram per 100 ml of blood or 5 microgram to 10 microgram per gram of the teeth. However, the scientists concede that this value still remains open to debate.

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